Dissertations / Theses on the topic 'Urea in soils'

Nitrogen (N) loss in the form of volatilized ammonia (NH₃) is a considerable problem when ammonium (NH₄⁺) forming fertilizers are applied to calcareous or alkaline soils. Large areas of agricultural land, contain alkalinity and salinity problems, are potentially suitable for crop production with little alteration. This study was conducted to determine and compare the effectiveness of urea phosphate (UP) in reducing soil alkalinity and NH₃ loss. The volatilization of NH₃ from UP and urea (U) was studied on 3 selected soils (Hayhook SL, Laveen L and Latene L) using an aeration system. Urea phosphate and U were each applied at rates of 0, 50, 100 and 200 ppm-N either to the surface dry or in solution or mixed with the soil. The volatilized NH₃ was trapped in sulfuric acid, sampled periodically and analyzed for N using the semi microkjeldahl distillation apparatus. The effect of UP, Sulfur-Foam (SF), Phosphuric Solution (PHP) and a mixture of SF and UP (Mix) on leaching soil sodium (Na) and salinity was also studies on two soils (Pima L and Crot CL) in columns. Each of these amendments was applied at a rate of one and two equivalent amounts of the exchangeable Naₑₓ. The highest N loss in the form of NH₃ occurred when U was applied to Hayhook soil. However, UP applied to Hayhook soil (neutral to acidic, coarse textured and low CaCO₃ content) resulted in the lowest NH₃-N loss. Less NH₃-N loss was found from U application to Laveen and Latene soils (fine textured with higher CaCO₃ content) than with Hayhook soil. The general trend was higher N loss, in the form of volatilized NH₃, with surface application dry or in solution than when mixed with the soil. This trend showed an increase in the amount of volatilized NH₃ with increasing rate of N application. Urea phosphate was as effective as PHP or Mix (acid containing fertilizers) treatments in reducing soil salinity and alkalinity in Pima and Crot soils. No difference was found between rates of application (1 and 2 equivalent amount of Naₑₓ) except for soil pH. A similar trend in the decrease in soil salinity was found to that of the pH which was in the order PHP, UP, Mix, SF and control treatments. No significant difference was found between SF and control treatments in all parameters. No significant difference was found between treatments for exchangeable Ca. This was affected by the Ca compounds present in the soil. Generally, UP is a potential fertilizer for supplying N and phosphorus (P) as plant nutrients, reducing NH₃ volatilization, and can be used as a soil amendment to control soil salinity and alkalinity.

Lignosulfonate (LS), a by-product of the pulp and paper industry, may have the potential to increase fertilizer N availability by acting as a urease and nitrification inhibitor. Four consecutive laboratory studies were conducted to evaluate the behavior of LS in agricultural soils. The effects of various types and rates of LS on soil respiration and soil N dynamics were determined. Effects of LS in combination with fertilizers on microbial activity and N dynamics were measured. Due to the high water solubility of LS a leaching column study was conducted to determine the potential leaching of LS.
Higher rates (20% w/w) of LS initially inhibited microbial activity. Generally LS was relatively resistant to degradation by soil microorganisms and small proportions of added LS-C ($<$2.1%) were leached from the soil columns, but leaching was a function of soil and moisture regime. Recovery of added mineral LS-N from soil treated with LS was low ($<$41%). Mineral N recovered from LS plus fertilizer amended soil was higher than recovery from corresponding fertilizer treatments. Lignosulfonate reduced urea hydrolysis and the proportion of added N volatilized as NH$ sb3$-N from a LS plus urea treatment. The mineral N pool from LS plus fertilizer treated soils had significantly lower NO$ sb3$-N concentrations than corresponding fertilizer treatments. Nitrification inhibition was believed to have been due to high fertilizer concentrations. At reduced urea and LS concentrations, LS decreased NO$ sb3$-N recovery in one of four soil types. However, reduced recovery may not have been from nitrification inhibition but possibly from denitrification or chemical reactions between N and phenolics from LS.

This thesis describes a series of experiments both in solution systems and soil systems to study the precipitation of calcium carbonate in soils and the effects of the precipitation on soil pH after urea had been applied. (1) A gas bubbling system has been established which introduces ammonia at a steady rate to the reaction solution and keeps it equilibrated at 0.00484 atm partial pressure of carbon dioxide. (2) In a non-seeded system, the effects of calcium, urea, Mg (magnesium), P (phosphate), and DOC (water-dissolved organic matter) on the precipitation were examined individually and in various combinations. Calcite and vaterite were found in the 10 mM CaC1₂ solutions with and without the addition of urea. When the solutions contained Mg, P, and DOC, vaterite was not found. Aragonite was found in the reaction solution containing 5 mM Mg. In high initial concentration of P (5x10^-4 M) , the formation of calcium phosphate (amorphous by X-ray analysis) catalysed the formation of calcite. The effects of urea and Mg on the precipitation are negligible compared with the effects of P and DOC. (3) In a seeded system, 16 sets of experiments with four sizes of calcite-seeds were carried out to study the precipitation rate of calcium carbonate. This was described by the equation LR=-4.113±0.132 + 0.379±0.029 LWA + LSI where LR=log (precipitation rate, PR, in mole litre^-1 min^-1), LWA= log (newly formed calcium carbonate, g ml^-1), and LSI=log (degree of supersaturation of calcium carbonate, SI). (4) A wide range of concentrations of urea (0.05, 0.1, 0.3, 0.5, 0.7, and 1 M) were added to three soils (Beg., Uni., and VWH) with or without the addition of 5 per cent of calcite (10-15 μm) to establish a rate model for the precipitation of calcium carbonate in soils. The precipitation model (in logarithmic form) in soils is lnPR=-9.47±0.30 + lnK_SOIL + 0.379±0.029 InWA + InSI - 1686±703 P - 6.13±3.02 DOC + 3854±1775 (P DOC) where P and DOC are the concentrations in soil solutions, and lnK_SOIL is the effect of soils on the precipitation, which is - 1.98, 0.43, and -0.10 for Beg., Uni., and VWH soils respectively. The amount of newly formed calcium carbonate is about a third to a half of the amount of ammoniacal-N released by urea hydrolysis. It was able to reduce the increase of soil pH by more than 0.6 pH units in some circumstances.

Understanding the redistribution and fate of N is essential for justification of Best Management Practices (BMP). This project was conducted on a Hecla fine sandy loam (sandy, mixed, Aquic Haploboroll) soil at the BMP field site near Oakes, North Dakota. One objective of this investigation was to evaluate the residence times of N03- -N in 20 undisturbed lysimeters and its infiltration time through the soil profile to tile drains. Corn (Zea mays L.) was fertilized with 135 kg N ha -1 as ??N-enriched urea plus 13.5 and 48.1 kg N ha -1 preplant for 1993 and 1994, respectively. Urea-N was band applied to 20 and 10 undisturbed lysimeters at 2.0 and 5.93 atom percent (at %) ??N in 1993 and 1994, respectively. Average resident times of N03- -N in the lysimeters was 11.7 months. Lysimeter and tile drainage indicate the presence of preferential pathways. Residence times of N03- -N depend on frequency and intensity of precipitation events. Another objective was to determine what portion of the total N in the crop was from applied urea-N and what portion was from the native soil-N. Nitrogen plots received ??N enrichments of 4.25 and 5.93 at % ??N in 1993 and 1994, respectively. At the end of the 1993 and 1994 growing season, 41.5% and 35.7% of the labeled fertilizer N remained in the soil profile, while the total recovery of applied ??N in the soil-plant system was 86.2% and 75.4%, respectively. Low recoveries of applied N may have been the result of soil or aboveground plant biomass volatilization, or denitrification or preferential flow processes. Further research needs to be conducted with strict accountability of gaseous loss and the mechanism(s) responsible.
U.S. Bureau of Reclamation

Fertilizer applications of urea and triple superphosphate (TSP) may affect availability of plant nutrients in the soil through alteration of soil pH and sorption-displacement effects. The objectives of this experiment were to evaluate urea and TSP effects on nutrient availability to soybean (Glycine max L.). Field experiments were carried out on three Quebec soils; a Chicot sandy clay loam (Gleyed Melanic Brunisol), an Ormstown silty clay loam (Luvic Gleysol) and a Ste. Rosalie clay (Humic Gleysol). Three levels of TSP (0, 40, 80 kg $ rm P sb2O sb5 ha sp{-1}),$ and three levels of urea (0, 25, 50 kg N ha$ sp{-1})$ were incubated in the field and sampled at 4, 8, 12, and 16 weeks. Added TSP increased extractable P and decreased NO$ sb3$-N. Overall, alterations in nutrients other than N and P with added TSP or urea were not agronomically significant. There was increased concentration of N, P and Mo in soybean in some soils due to TSP application. Added urea increased Mg concentration in soybean. The concentration and uptake of Mo was positively correlated with soil extractable P and Mg. Consequently, application of TSP and urea together improved Mo uptake in the Chicot soil, while in slightly acid soils, Ormstown and Ste. Rosalie, TSP alone increased Mo uptake.

Thesis (M.S.)--University of Missouri-Columbia, 2008.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on September 12, 2008) Includes bibliographical references.

To date, there has been little research into the role of microbial community structure in the functioning of the soil ecosystem and on the links between microbial biomass size, microbial activity and key soil processes that drive nutrient availability. The maintenance of structural and functional diversity of the soil microbial community is essential to ensure the sustainability of agricultural production systems. Soils of the same type with similar fertility that had been under long-term organic and conventional crop management in Canterbury, New Zealand, were selected to investigate relationships between microbial community composition, function and potential environmental impacts. The effects of different fertilisation strategies on soil biology and nitrogen (N) dynamics were investigated under field (farm site comparison), semi-controlled (lysimeter study) and controlled (incubation experiments) conditions by determining soil microbial biomass carbon (C) and N, enzyme activities (dehydrogenase, arginine deaminase, fluorescein diacetate hydrolysis), microbial community structure (denaturing gradient gel electrophoresis following PCR amplification of 16S and 18S rDNA fragments using selected primer sets) and N dynamics (mineralisation and leaching). The farm site comparison revealed distinct differences between the soils in microbial community structure, microbial biomass C (conventional > organic) and arginine deaminase activity (organic > conventional). In the lysimeter study, the soils were subjected to the same crop rotation (barley (Hordeum vulgare L.), maize (Zea mays L.), rape (Brassica napus L. ssp. oleifera (Moench)) plus a lupin green manure (Lupinus angustifolius L.) and two fertiliser regimes (following common organic and conventional practice). Soil biological properties, microbial community structure and mineral N leaching losses were determined over 2½ years. Differences in mineral leaching losses were not significant between treatments (total organic management: 24.2 kg N per ha; conventional management: 28.6 kg N per ha). Crop rotation and plant type had a larger influence on the microbial biomass, activity and community structure than fertilisation. Initial differences between soils decreased over time for most biological soil properties, while they persisted for the enzyme activities (e.g. dehydrogenase activity: 4.0 and 2.9 µg per g and h for organic and conventional management history, respectively). A lack of consistent positive links between enzyme activities and microbial biomass size indicated that similarly sized and structured microbial communities can express varying rates of activity. In two successive incubation experiments, the soils were amended with different rates of a lupin green manure (4 or 8t dry matter per ha), and different forms of N at 100 kg per ha (urea and lupin) and incubated for 3 months. Samples were taken periodically, and in addition to soil biological properties and community structure, gross N mineralisation was determined. The form of N had a strong effect on microbial soil properties. Organic amendment resulted in a 2 to 5-fold increase in microbial biomass and enzyme activities, while microbial community structure was influenced by the addition or lack of C or N substrate. Correlation analyses suggested treatment-related differences in nutrient availability, microbial structural diversity (species richness or evenness) and physiological properties of the microbial community. The findings of this thesis showed that using green manures and crop rotations improved soil biology in both production systems, that no relationships existed between microbial structure, enzyme activities and N mineralisation, and that enzyme activities and microbial community structure are more closely associated with inherent soil and environmental factors, which makes them less useful as early indicators of changes in soil quality.

Soil P fractionation was used to examine changes in soil inorganic and organic P under grazed irrigated pasture in a long-term field trial at Winchmore in Mid-Canterbury. The soil P fractionation scheme used involved sequential extractions of soil with O.5M NaHCO₃ @ pH 8.5 (NaHCO₃ P), 0.1M NaOH (NaOH I P), 1M HCl (HCl P) and 0.1M NaOH (NaOH II P). The Winchmore trial comprised 5 treatments: control (no P since 1952), 376R (376 kg superphosphate ha⁻¹ yr⁻¹ 1952-1957, none since), 564R (564 kg superphosphate ha⁻¹ yr⁻¹ 1952-1957, none since) 188PA (188 kg superphosphate ha⁻¹ yr⁻¹ since 1952) and 376PA (376 kg superphosphate ha⁻¹ yr⁻¹ since 1952: Topsoil (0-7.5cm) samples taken from the different treatments in 1958, 1961, 1965, 1968, 1971, 1974 and 1977 were used in this study. Changes in soil P with time showed that significant increases in soil inorganic P occurred in the annually fertilised treatments (l88PA, 376PA). As expected, the overall increase in total soil inorganic P between 1958 and 1977 was greater in the 376PA treatment (159 µg P g⁻¹) than that in the 188PA treatment (37 µg P g⁻¹). However, the chemical forms of inorganic P which accumulated in the annually fertilised treatments changed with time. Between 1958 and 1971 most of the increases in soil inorganic P in these treatments occurred in the NaHCO₃ and NaOH I P fractions. On the other hand, increases in soil inorganic P in the annually fertilised treatments between 1971 and 1977 were found mainly in the HCl and NaOH II P fractions. These changes in soil P forms were attributed to the combined effects of lime addition in 1972 and increased amounts of sparingly soluble apatite P and iron-aluminium P in the single superphosphate applied during the 1970's. In the residual fertiliser treatments (376R, 564R) significant decreases in all of the soil inorganic P fractions (i.e. NaHCO₃ P, NaOH I P, HCl P, NaOH II p) occurred between 1958 and 1977 following the cessation of P fertiliser inputs in 1957. This was attributed to continued plant uptake of P accumulated in the soil from earlier P fertiliser additions. However, levels of inorganic P in the different soil P fractions in the residual fertiliser treatments did not decline to those in the control which indicated that some of the inorganic P accumulated in the soil from P fertiliser applied between 1952 and 1957 was present in very stable forms. In all treatments, significant increases in soil organic P occurred between 1958 and 1971. The overall increases in total soil organic P were greater in the annually fertilised treatments (70-86 µg P g⁻¹) than those in the residual fertiliser (55-64 µg P g⁻¹) and control (34 µg P g⁻¹) treatments which reflected the respective levels of pasture production in the different treatments. These increases in soil organic P were attributed to the biological conversion of native and fertiliser inorganic P to organic P in the soil via plant, animal and microbial residues. The results also showed that annual rates of soil organic P accumulation between 1958 and 1971 decreased with time which indicated that steady-state conditions with regard to net 'organic P accumulation were being reached. In the residual fertiliser treatments, soil organic P continued to increase between 1958 and 1971 while levels of soil inorganic P and pasture production declined. This indicated that organic P which accumulated in soil from P fertiliser additions was more stable and less available to plants than inorganic forms of soil P. Between 1971 and 1974 small (10-38 µg P g⁻¹) but significant decreases in total soil organic P occurred in all treatments. This was attributed to increased mineralisation of soil organic P as a result of lime (4 t ha⁻¹) applied to the trial in 1972 and also to the observed cessation of further net soil organic P accumulation after 1971. Liming also appeared to affect the chemical nature of soil organic P as shown by the large decreases in NaOH I organic P(78-88 µg P g⁻¹) and concomitant smaller increases in NaOH II organic P (53-65 µg P g⁻¹) which occurred in all treatments between 1971 and 1974. The chemical nature of soil organic P in the Winchmore long-term trial was also investigated using 31p nuclear magnetic resonance (NMR) spectroscopy and gel filtration chromatography. This involved quantitative extraction of organic P from the soil by sequential extraction with 0.1M NaOH, 0.2M aqueous acetylacetone (pH 8.3) and 0.5M NaOH following which the extracts were concentrated by ultrafiltration. Soils (0-7.5cm) taken from the control and 376PA annually fertilised treatments in 1958, 1971 and 1983 were used in this study. 31p NMR analysis showed that most (88-94%) of the organic P in the Winchmore soils was present as orthophosphate monoester P while the remainder was found as orthophosphate diester and pyrophosphate P. Orthophosphate monoester P also made up almost all of the soil organic P which accumulated in the 376PA treatment between 1958 and 1971. This indicated that soil organic P in the 376PA and control treatments was very stable. The gel filtration studies using Sephadex G-100 showed that most (61-83%) of the soil organic P in the control and 376PA treatments was present in the low molecular weight forms (<100,000 MW), although the proportion of soil organic P in high molecular weight forms (>100,000 MW) increased from 17-19% in 1958 to 38-39% in 1983. The latter was attributed to the microbial humification of organic P and indicated a shift toward more complex and possibly more stable forms of organic P in the soil with time. Assuming that the difference in soil organic P between the control and 376PA soils sampled in 1971 and 1983 represented the organic P derived from P fertiliser additions, results showed that this soil organic P was evenly distributed between the high and low molecular weight fractions. An exhaustive pot trial was used to examine the relative availability to plants of different forms of soil inorganic and organic P in long-term fertilised pasture soils. This involved growing 3 successive crops of perennial ryegrass (Lolium perenne) in 3 Lismore silt loam (Udic Ustochrept) soils which had received different amounts of P fertiliser for many years. Two of the soils were taken from the annually fertilised treatments in the Winchmore long term trial (188PA, 376PA) and the third (Fairton) was taken from a pasture which had been irrigated with meatworks effluent for over 80 years (65 kg P ha⁻¹ yr⁻¹). Each soil was subjected to 3 treatments, namely control (no nutrients added), N100 and N200. The latter treatments involved adding complete nutrient solutions with different quantities of N at rates of 100kg N ha⁻¹ (N100) and 200kg N ha⁻¹ (N200) on an area basis. The soil P fractionation scheme used was the same as that used in the Winchmore long-term trial study (i.e. NaHCO₃ P, NaOH I P, HCl P, NaOH II p). Results obtained showed that the availability to plants of different extracted inorganic P fractions, as measured by decreases in P fractions before and after 3 successive crops, followed the order: NaHCO₃ P > NaOH I P > HCl P = NaOH II P. Overall decreases in the NaHCO₃ and NaOH I inorganic P fractions were 34% and 16% respectively, while corresponding decreases in the HCl and NaOH II inorganic P fractions were small «10%) and not significant. However, a significant decrease in HCl P (16%) was observed in one soil (Fairton-N200 treatment) which was attributed to the significant decrease in soil pH (from 6.2 to 5.1) which occurred after successive cropping. Successive cropping had little or no effect on the levels of P in the different soil organic P fractions. This indicated that net soil organic P mineralisation did not contribute significantly to plant P uptake over the short-term. A short-term field experiment was also conducted to examine the effects of different soil management practices on the availability of different forms of P to plants in the long-term fertilised pasture soils. The trial was sited on selected plots of the existing annually fertilised treatments in the Winchmore long-term trial (188PA, 376PA) and comprised 5 treatments: control, 2 rates of lime (2 and 4 t ha⁻¹ ) , urea fertiliser (400kg N ha⁻¹ ) and mechanical cultivation. The above ground herbage in the uncultivated treatments was harvested on 11 occasions over a 2 year period and at each harvest topsoil (0-7.5 cm) samples were taken from all of the treatments for P analysis. The soil P fractionation scheme used in this particular trial involved sequential extractions with 0.5M NaHCO₃ @ pH 8.5 (NaHCO₃ P), 0.1M NaOH (NaOH P), ultrasonification with 0.1M NaOH (sonicate-NaOH p) and 1M HCl (HCl P). In addition, amounts of microbial P in the soils were determined. The results showed that liming resulted in small (10-21 µg P g⁻¹) though significant decreases in the NaOH soil organic P fraction in the 188PA and 376PA plots. Levels of soil microbial P were also found to be greater in the limed treatments compared with those in the controls. These results indicated that liming increased the microbial mineralisation of soil organic P in the Winchmore soils. However, pasture dry matter yields and P uptake were not significantly affected. Although urea significantly increased dry matter yields and P uptake, it did not appear to significantly affect amounts of P in the different soil P fractions. Mechanical cultivation and the subsequent fallow period (18 months) resulted in significant increases in amounts of P in the NaHCO₃ and NaOH inorganic P fractions. This was attributed to P released from the microbial decomposition of plant residues, although the absence of plants significantly reduced levels of microbial P in the cultivated soils. Practical implications of the results obtained in the present study were presented and discussed.

Fertilizer nitrogen transformations in two Sitka spruce stands in northeast Scotland were studied using 15N-labelled (2.5 atom % 15N) urea at a rate equivalent to 160 kg N ha-1. The use of urea fertilizer resulted in accelerated growth of the tree crowns, and higher concentrations of total N in foliage, twigs and new wood. There was no fertilizer effect observed for bark. Despite a positive growth response by the trees to fertilizer N, only an estimated 17% of applied-N was utilized by the tree biomass. Application of urea-N resulted in a reduction in the leaching of inorganic N and certain cations (particularly Ca 2+). Gaseous losses of N were elevated following urea application, but estimated losses of fertilizer N via NH3 volatilization and denitrification were negligible. Data from both sites indicated a retention of volatilized NH3 in the tree canopy which was returned to the soil in throughfall. Urea application to the forest floor resulted in elevated pH of the LFH for a period of about 100 days. Urea application also led to a flush of acetic acid extractable PO4-P in the LFH. The addition of urea also resulted in increased counts of bacteria in the LFH. Data indicacted that elevated NO3- concentrations in the LFH may have been due to bacterial nitrification. Little effect of fertilizer N was observed for mineral soil, with a retention of the bulk of fertilizer N in the LFH.

Low recovery rates of fertiliser N in tree biomass are frequently reported due to the inefficiency of N fertilisers in afforested ecosystems. At Culloden (North East Scotland), only 13&'37 of 15N-urea fertiliser applied to Sitka spruce could be recovered in the above-ground tree biomass two years after fertilisation. Fertiliser N not taken up by trees was largely 'locked-up' in stable organic forms of N within the LFH layers of the soil profile. 15N-labelled litter was used in both field and microcosm experiments, the release and fate of litter-derived-N (LDN) being traced over the course of two growing seasons. In both experiments, the microbial biomass acted as a major sink for LDN. Measurement of soil microbial biomass was calibrated for Culloden soil samples by determination of a kEN-factor. Tree uptake of LDN, in the field, occurred within one month of labelled-litter application, with the foliage being the largest sink for LDN. Approximately 30&'37 of the N within the labelled-litter layer was taken up by the trees over the course of two growing seasons and was equivalent to 5.4 kg LDN ha-1 y-1. There was considerable mixing of the LFH and peat layers in Sitka spruce microcosm soil profiles. This was probably due to elevated soil animal population densities. After 18 months, approximately 83&'37 of LDN had been redistributed to other N pools in the microcosm. Uptake of LDN by seedlings accounted for 15.7&'37 of LDN after 12 months, the largest sink being the foliage, equivalent to 6.16 kg LDN ha-1 y-1. Again, the microbial biomass was a major sink for LDN. Measurement of availability (NH4+) N in Culloden soil samples incubated at different matric potentials and temperatures, appeared not to reflect N mineralisation rates. There was a strong interaction between temperature and soil matric potential, seedling uptake of N being greatest at 15oC and -16.0 kPa. The rate of turnover of the microbial biomass pool was identified as the key determinant of the rate of processing of LDN in forest soils.

The potential for improved fertilizer nitrogen (N) use efficiency (NUE) and yield in winter wheat (Triticum aestivum L.) and maize (Zea mays L.) was tested using a new, controlled release urea formaldehyde polymer (UFP). This polymer was compared with conventional aqueous urea-ammonium nitrate (UAN) [(NH2)2CO?NH4NO3] fertilizer during a two-year field experiment in North Carolina from 2004 to 2006. The crops were grown on three soils: Candor (sandy, siliceous, thermic Grossarenic Kandiudult), Portsmouth (fine-loamy over sandy or sandy-skeletal, mixed, semiactive, thermic Typic Umbraquult) and Cape Fear (fine, mixed, semiactive, thermic Typic Umbraquult). The sandy soil was irrigated as needed to avoid drought stress. Treatments were N source (UAN and UFP) and N rate (0, 50, 78, 106, 134, 162, and 190 kg N ha-1 or 0, 45, 70, 95, 120, 145, and 170 lb ac-1 for wheat and 0, 39, 78, 118, 157, 196, and 235 kg N ha-1 or 0, 35, 70, 105, 140, 175, and 210 lb ac-1 for maize) arranged as randomized complete blocks with four replications. The UAN and UFP were applied as a split application for wheat, while maize received UFP at planting and split UAN. Timing of the materials was determined either by label (UFP) or prior experimental experience (UAN). Harvest biomass, grain, and mid-season soil sampling were performed to assess N availability. For both crops, UAN performed statistically similar to or better than UFP at both sites with regards to yields and NUE. Also, soil sampling and incubation results showed no consistent difference between N sources, implying the slow release properties of the UFP were not seen under the site and laboratory conditions. The release time for both sources at both sites was approximately 14 days (2 weeks). Since the cost of UFP is substantially greater than UAN and form did not significantly affect yield, UFP may not be as economical as UAN, depending on pricing of the different fertilizers.

Application of water and fertilizer through buried drip lines shows promise for vegetable production in Arizona. Use of an acidic product is necessary if phosphorus is added through the system. Urea phosphate was shown to be a satisfactory product for injecting into buried drip lines for squash and cabbage.

In the present thesis, implications of pasture establishment, fertilization and abandonment on soil C and nutrient dynamics were investigated for the mountain rainforest region of southern Ecuador. Over the past decades the natural forest of the study area has been threatened by conversion to cattle pastures. However, the soil fertility of these extensively grazed pastures (active pastures) declines continuously during pasture use. The invasion of bracken fern (Pteridium arachnoideum) leads to pasture abandonment when bracken becomes dominant. In order to reveal the mechanisms behind the deterioration of soil fertility, biotic and abiotic soil properties and their interaction were analyzed along a land‐use gradient (natural forest – active pasture – abandoned pasture). The ecosystem disturbance of the mountain rainforest through pasture use changed the microbial function and structure, and affected soil CO2‐C fluxes. Annually, 2 Mg soil CO2‐C ha‐1 were additionally emitted from the pasture land. This acceleration in soil respiration rates was related to accelerated rates of microbial C mineralization and fine‐root respiration. The high‐quality, N‐rich above‐ and belowground residues of the pasture grass (S. sphacelata, C4‐plant), especially the huge fine‐root biomass, provided a high C and N availability for soil microbes. Compared to the forest, increased soil pH and accelerated base saturation were further factors beneficial for soil microbial growth and metabolism of the upper mineral soil at active pastures. Three times higher amounts of microbial biomass C and a significant shift in the microbial community structure towards a higher relative abundance of Gram(‐)‐ bacteria and fungi were observed. Long‐term pasture use and the invasion of bracken (C3‐plant) diminished beneficial effects for microbes, causing a significant decrease in the C, net, and gross N mineralization rates as well as a two‐third reduction in the microbial biomass. A preferential substrate utilization of grass‐derived C4 by the soil microbes resulted in a rapid decline of the C4‐pool. As a consequence, the less available C3‐pool from bracken and former forest increased its dominance in the SOC‐pool, further decreasing pasture productivity and finally causing pasture abandonment. The lower quality and quantity of above‐ and belowground residues of the bracken (high lignin content, C/N) resulted in resource‐limited conditions that influenced the microbial function to greater extent than their structure. The microbial structure seemed to be sensitive mainly to soil pH along the land‐use gradient. Thus, a disconnection between microbial structure and function was identified. Fertilization experiments were conducted both in the lab and in the field to evaluate the impact of urea and/or rock phosphate amendment on SOM dynamics and on pasture productivity of active pastures. After combined fertilization the pasture yield was most efficiently increased by 2 Mg ha−1 a−1, indicating a NP‐limitation of grass growth. Furthermore, the fodder quality was improved by a higher content of P and Ca in the grass biomass. The microorganisms of the active pasture soil responded with an adaptation of their structure to the increased substrate availability in the short term, but did not change their initial functions in the long term. After urea/ rock phosphate addition a significant increase in the relative fungal abundance was detected, but neither a microbial limitation of energy nor of N or P was observed. However, urea addition accelerated gaseous losses of soil CO2‐C in the short term. In the study area, pronounced alterations in ecosystem functioning due to land‐use changes were detected, especially in soil C and N cycling rates. For a sustainable land‐use in this region it is crucial to prevent pasture degradation and to rehabilitate degraded pastures in order to protect the prevailing mountain rainforest ecosystem. It is of crucial importance for active pasture soils to maintain or even increase resource availability, being one indicator of soil fertility. In this context, the soil organic matter has to be retained in the long‐term to maintain high microbial activity and biomass, and thus pasture productivity. A moderate fertilization with urea and rock phosphate can be a first step to provide continuous nutrient supply for grass growth and to strengthen livestock health through increased fodder quality. However, the risk of further additional emissions of soil CO2‐C due to increased loads of urea fertilizer application has to be kept in mind. Overall, for the establishment of a sustainable land‐use management the control of bracken invasion and an adjusted nutrient management are needed. Further investigations on the reduction of soil nutrient losses and increased nutrient use efficiencies of plants, such as combined planting with legumes or the usage of cultivars with special nutrient acquisition strategies, should be in the focus of future work
In der vorliegenden Dissertation werden die Auswirkungen der Weideetablierung, ‐düngung sowie des Verlassens von Weiden auf Bodenkohlenstoff‐ und Nährstoffdynamik in einer tropischen Bergregenwaldregion Ecuadors zusammenfassend dargestellt und diskutiert. Der Naturwald des Untersuchungsgebietes ist seit Jahrzehnten durch Brandrodung und die Umwandlung in extensiv genutztes Weideland (aktive Weide) in seinem flächenhaften Bestand bedroht. Als Problem hat sich der Verlust an Fruchtbarkeit der Weideböden während ihrer Bewirtschaftung herausgestellt. Des Weiteren führt die Einwanderung des Tropischen Adlerfarns (Pteridium arachnoideum, C3‐Pflanze) zu einer Reduktion der oberirdischen Grasbiomasse. Nimmt diese Entwicklung überhand, werden die betroffenen Flächen von den Bauern nicht mehr aktiv genutzt, verlassen und neuer Regenwald gerodet. Um mehr über die Mechanismen der Verringerung der Bodenfruchtbarkeit zu erfahren, wurden biotische und abiotische Bodeneigenschaften und deren Interaktion entlang eines Landnutzungsgradienten (Naturwald – aktive Weide – verlassene Weide) untersucht. Die Zerstörung des Bergregenwaldökosystems und die Überführung der gerodeten Flächen zur Weidebewirtschaftung verändert die Funktion und Struktur der Bodenmikroorganismen und beeinflusst den CO2‐C Fluss aus dem Boden. Jährlich werden 2 t CO2‐C ha‐1 zusätzlich vom Weideland emittiert. Diese Erhöhung der Bodenatmungsraten kann mit erhöhten Raten der mikrobiellen C‐Mineralisierung und Feinwurzelatmung in Verbindung gebracht werden. Das Weidegras (S. sphacelata, C4‐Pflanze) liefert C‐ und N‐reiche ober und unterirdische organische Substanz (z.B. durch die Feinwurzelbiomasse) und trägt damit zu einer Erhöhung der C‐ und N‐Verfügbarkeit für die mikroorganismen bei. Darüber hinaus stellen ein höherer pH‐Wert und eine erhöhte Basensättigung im oberen Mineralboden der aktiven Weide günstige Bedingungen für mikrobielles Wachstum und Metabolismus dar. Als Konsequenz sind die Gehalte an mikrobiellem Biomassekohlenstoff um das Dreifache erhöht und die mikrobiellen Gemeinschaftsstrukturen signifikant in Richtung einer höheren relativen Abundanz der Gram(‐)‐Bakterien und Pilze verschoben. Eine längerfristige Weidebewirtschaftung ohne Kompensation von Nährstoffverlusten sowie die Einwanderung des Tropischen Adlerfarnes verschlechterte die Bedingungen für die Mikroorganismen, was zu einem signifikanten Rückgang des SOC, der Netto‐ und Brutto‐N‐Mineralisierungsraten sowie zu einer Halbierung der mikrobiellen Biomasse führt. Eine bevorzugte Substratnutzung von Graskohlenstoff (C4) durch die Mikroorganismen hat einen schnellen Abbau des C4‐Pools zur Folge. Somit dominiert nun der mikrobiell schlechter verfügbare C3‐Pool den Bodenkohlenstoffpool. Dies führt zu einem weiteren Rückgang der Weideproduktivität und schließlich zum Offenlassen der Weide. Die geringere Qualität und Quantität der vom Farn stammenden ober‐ und unterirdischen organischen Substanz (hoher Ligninanteil, weites C/N), führten zu einer Limitierung der Ressourcen für die Mikroorganismen, welche deren Funktionen in größerem Maße beeinflussen als deren Gemeinschaftsstruktur. Im Gegensatz dazu wird entlang des Landnutzungsgradienten die Struktur hauptsächlich durch den pH‐Wert beeinflusst. Daraus folgt, dass Struktur und Funktion der Bodenmikroorganismen voneinander entkoppelt auf Veränderungen reagieren können. Um den Einfluss von Harnstoff‐ und/ oder Rohphosphatdüngung aktiver Weiden auf die Dynamik der organischen Bodensubstanz und auf die Weideproduktivität zu untersuchen, wurden sowohl Labor‐ als auch Feldversuche durchgeführt. Im Feldexperiment wurde gezeigt, dass eine NP‐Limitierung der Grasbiomasseproduktion vorliegt und durch eine geringe NP‐Kombinationsdüngung die oberirdische Phytomasseproduktion um 2 t ha−1 a−1 gesteigert und die Futterqualität durch eine Erhöhung der P‐ und Ca‐ Gehalte verbessert werden kann. Die Mikroorganismen reagierten mit einer Anpassung ihrer Struktur an die kurzzeitig erhöhte Substratverfügbarkeit. Nach Gabe von Harnstoff und/ oder Rohphosphat wurde weder eine N‐ noch eine P‐Limitierung der Bodenmikroorganismen festgestellt, und die mikrobiellen Funktionen wurden langfristig nicht verändert. Dagegen bewirkte die Düngergabe einen erhöhten relativen Anteil der Pilzabundanz. Im Labor sowie im Feld kam es nach Harnstoffdüngung kurzzeitig zu verstärkten gasförmigen Verlusten des Bodenkohlenstoffs. Aufgrund der Landnutzungsänderungen im Untersuchungsgebiet veränderten sich die Ökosystemfunktionen stark, speziell die Boden‐C‐ und Boden‐N‐Umsatzraten. Für eine nachhaltige Landnutzung in der Region, d. h., für den Schutz der noch verbliebenen natürlichen Bergregenwaldflächen, ist es von entscheidender Bedeutung, dass die Weidedegradierung verhindert wird und degradierte Flächen wieder in Nutzung genommen werden. Als entscheidend für die Weideproduktivität hat sich in dieser Studie die Ressourcenverfügbarkeit für Bodenmikroorganismen herausgestellt. Daher ist es sehr wichtig, diese Ressourcenverfügbarkeit in Böden aktiv‐genutzter Weiden zu erhalten oder noch zu erhöhen, denn sie wirkt sich vor allem auf die organische Bodensubstanz und im Wechselspiel damit auf die mikrobielle Biomasse und Aktivität aus. Eine moderate Kombinationsdüngung aus Harnstoff und Rohphosphat ist ein erster Schritt in diese Richtung. Dabei sollte jedoch das Risiko zusätzlicher bodenbürtiger CO2‐C Emissionen in Folge höherer Düngergaben berücksichtigt werden. Für ein nachhaltiges Landnutzungsmanagement sind Maßnahmen gegen die Einwanderung des Adlerfarnes und ein angepasstes Nährstoffmanagement notwendig. Weitere Untersuchungen sollten auf eine Minimierung der Nährstoffverluste und eine erhöhte Nährstoffnutzungseffizienz der Pflanzen fokussiert werden. Weidemischkulturen aus Gräsern mit Leguminosen sowie der Einsatz von Kulturen mit speziellen Nährstoffaneignungsstrategien könnten dabei eine große Rolle spielen und sollten in der Region erprobt werden
La tesis presentada investiga el impacto del establecimiento de pasto, de su fertilización y de su manejo tradicional (abandono del pastizal) a la dinámica del carbono y de los nutrientes de suelo en la región de los bosques tropicales montañosos en el Sur de Ecuador. Durante las últimas décadas el bosque natural en el área de estudio ha estado amenazada por su conversión a pastizales. Sin embargo, la fertilidad del suelo en pastos de tipo extensivo (pastos activos) decrece frecuentemente durante el uso de los pastos. La invasión de Llashipa (Pteridium arachnoideum) conduce al abandono de los pastos cuando la ésta se vuelve dominante. Con la finalidad de revelar los mecanismos detrás de esta disminución de la fertilidad de suelo, se analizaron las propiedades bióticas y abióticas del suelo y sus interacciones, a lo largo de una gradiente del uso de la tierra (bosque natural —pasto activo — pastos abandonados). La perturbación del ecosistema de bosque tropical montañoso por su cambio de uso, mediante el establecimiento de pastizales, ha alterado la función y la estructura de los microorganismos y ha afectado el flujo de CO2‐C del suelo. Cada año 2 Mg CO2‐C ha‐1 fueron emitidas adicionalmente por el establecimiento de pastos. Esta aceleración en la tasa de respiración del suelo está relacionada con el aumento de las tasas de mineralización microbiana de carbono y de la respiración de las raíces. La alta calidad y abundancia de N de los residuos orgánicos del suelo con pasto Mequeron (S. sphacelata, C4‐planta), especialmente debido a la gran biomasa de las raíces finas, ofrecen una disponibilidad alta de C y N para los microorganismos. En comparación con el bosque natural, el aumento del pH y la saturación bases acelerada fueron condiciones más favorables para el crecimiento microbiano y para el metabolismo microbiano en el parte superior del suelo mineral en pastos activos. La cantidad de C de la biomasa de los microorganismos fue tres veces mayor que la del bosque y se ha observado un cambio significativo de la estructura de la comunidad microbiana, en donde la abundancia relativa de los hongos y de las bacterias Gram(‐) ha aumentado. El uso de pasto a largo plazo y la invasión de Llashipa (C3‐planta) han reducido los efectos benéficos para los microorganismos, que resultaron en una reducción significativa de las tasas de la mineralización de C y N, y en una reducción en dos tercios de la biomasa microbiana. El uso preferencial de los microorganismos por sustrato de pasto C4 han resultado en una rápida disminución de la reserva de C4. Como consecuencia, la menor disponibilidad de la reserva de C3 de las plantas de Llashipa y de la cobertura anterior de bosque ha incrementado su dominancia en la reserva de materia orgánica del suelo. Eso resulta, en una mayor disminución de la productividad de los pastos, conduciendo finalmente al abandono de los campos de pastos. La menor calidad y cantidad de los residuos acumulados sobre y bajo el suelo provenientes de la Llashipa han dado como resultado un sustrato de limitadas condiciones que están afectando más a las funciones microbiales antes que a su estructura. La estructura microbiana parece ser más sensible al pH del suelo a largo de la gradiente del uso de la tierra; de manera que se ha identificado una desconexión entre la estructura y función microbial. Experimentos de fertilización en laboratorio y en campo han sido realizados para evaluar el impacto de la aplicación de enmiendas (urea y/o roca fosfórica) a la dinámica de la materia orgánica y a la productividad de los pastos activos. El resultado del experimento de campo ha demostrado que la fertilización combinada es más efectiva, mostrando un aumento en la producción de biomasa de 2 Mg ha−1 a−1, lo que indica una limitación de N y P para el crecimiento del pasto. Además, la calidad de forraje se mostró incrementada ya que el contenido de P y de Ca han aumentado significativamente. Los microorganismos del suelo en el pasto activo han respondido a corto plazo con una adaptación de su estructura ante la disponibilidad de sustrato, pero no han mostrado un cambio de sus funciones iniciales a largo plazo. Después de la aplicación de urea y de la roca fosfórica, se detectó un incremento significativo en la abundancia de los hongos, pero tampoco se observó una limitación de energía microbial ni de N o P. Sin embargo, la aplicación de urea ha aumentado la pérdida gaseosa de CO2‐C del suelo a corto plazo. Debido al cambio de uso de la tierra en la área de investigación, se ha detectado una alteración notable de la función del ecosistema, especialmente en el ciclo de C y N de suelo. Para un uso sostenible de la tierra en esta región, es crucial el prevenir la degradación de pastos y rehabilitar aquellos degradados. En el suelo de pastos activos es de gran importancia el mantener o aún mejor el aumentar la disponibilidad del sustrato, que es uno de los indicadores de la fertilidad del suelo. En este contexto, la materia orgánica se debe ser retenida a largo plazo para mantener la actividad y biomasa microbiana alta y por ende la productividad de pasto. Una moderada fertilización con urea y roca fosfórica puede ser un primer paso para proveer un continuo suministro de nutrientes por el crecimiento del pasto y para reforzar la sanidad pecuaria por medio de un forraje de mayor calidad. Sin embargo, el riesgo de emisiones adicionales de CO2‐C del suelo debido a una aplicación más alta de urea debe tenerse en cuenta. Se puede concluir que para un manejo sostenible del uso de la tierra, tanto el control de la invasión de Llashipa y como un suministro adecuado de nutrientes son necesarios. Adicionalmente se podría decir que es necesario profundizar el estudio de la reducción de las pérdidas de los nutrientes de suelo y de la eficiencia del uso de los nutrientes en las plantas, así como las asociaciones de pastos con leguminosas o el uso de cultivos de absorción selectiva de nutrientes, que serían estrategias importantes para el futuro

AN ABSTRACT OF THE THESIS OF BRENT C. SUNDERLAGE, for the Master of Science degree in Plant, Soil, and Agricultural Systems, presented on March 8, 2017, at Southern Illinois University Carbondale. TITLE: LATE APPLICATION NITROGEN ON CORN IN SOUTHERN ILLINOIS AND SOIL PROPERTIES AFFECTING AMMONIA VOLATILIZATION FROM UREA FERTILIZER MAJOR PROFESSOR: Dr. Rachel L. Cook In corn (Zea mays L.) production systems, typical nitrogen fertilization occurs either before planting or after crop emergence, as late as the V6 stage. Since the majority of nitrogen uptake does not occur until V10 through R1, delaying nitrogen fertilization until V10 may reduce potential for early season soil N transformations and losses, while sustaining crop yields. A two-year study, conducted across three southern Illinois locations, evaluated the effects of various late sidedress nitrogen applications and enhanced efficiency fertilizers on corn yield and residual mineral soil N. The various nitrogen treatments compared: rates from 0-224 kg N ha-1; sources of urea and 32% UAN, with and without urease inhibitors 0.09% N-(n-butyl) thiophosphoric triamide (NBPT) as Agrotain® Ultra (AT) and 0.06% NBPT + 0.02% N-(n-propyl) thiophosphoric triamide (NPPT) as Limus® (L), and polymer-coated urea (ESN®); application timings at planting, V6, V10, and VT; placement either dribble applied, broadcasted, or injected. Across sites and years, late (V10) nitrogen split applications generally resulted in corn yields greater than or equal to the same total nitrogen rate applied at planting. Most late N treatment differences varied between sites and years, but 56 kg N ha-1 as broadcasted UAN at planting with 112 kg N ha-1 as broadcasted urea, either with or without AT or L at V10 were on average highest yielding treatments among sites in both years, with 16% greater yield than 168 kg N ha-1 as broadcasted UAN at planting. Urease inhibitors did not enhance yield in most instances, likely due to sufficient incorporating rainfall shortly after application. The effects of urease inhibitors used with late-application nitrogen on corn yield and actual ammonia volatilization remained ambiguous. Residual soil mineral nitrogen concentrations between 0-30 cm after harvest in the late nitrogen treatments did not elicit water quality concerns. Furthermore, ammonia volatilization from surface applied urea is controlled by many interrelated soil properties as well as environmental conditions. However, conclusions about the influence of soil properties on ammonia volatilization differ according to geographies and are not well established across a wide range of soil types. A laboratory soil incubation experiment measured the effects of soil properties on ammonia volatilization over 7 days from surface-applied urea and the efficacy of three urease inhibitors: Agrotain® Ultra (AT) as 0.09% NBPT, Limus® (L) as 0.06% NBPT + 0.02% NPPT, and NutriSphere-N® (NS) 30% calcium salt of maleic-itaconic copolymer among 83 soil surface samples from across the United States with a wide range of soil properties. The soil properties evaluated were: total exchange capacity, 1:1 CaCl2 pH, organic matter, buffering capacity, clay content, and urease activity. In Urea (R2 = 0.69) and Urea + NS (R2 = 0.62) models, total exchange capacity, clay, and buffering capacity significantly reduced ammonia volatilization, and organic matter significantly increased ammonia volatilization, while 1:1 CaCl2 pH and urease activity were non-significant. Clay, organic matter, and buffering capacity were correlated to total exchange capacity. Total exchange capacity was the strongest predictor and best consolidated variable to predict N loss of urea. In Urea + AT (R2 = 0.54) and Urea + L (R2 = 0.67) models, ammonia volatilization was significantly reduced at lower 1:1 CaCl2 pH and total exchange capacity, and all other soil properties were non-significant. The NBPT in Urea + AT and Urea + L likely decayed more rapidly under acidic soil conditions, resulting reduced NBPT efficacy and greater N loss at lower pH. Urea + AT and Urea + L reduced volatilization significantly by 18.2 percentage points compared to Urea or Urea + NS, and there were no significant differences between Urea + AT and Urea + L (α = 0.05). On average, NutriSphere-N® did not reduce volatilization.

Background: Soil transmitted helminth infections (STHI) are important Neglected Tropical Diseases (NTD). The three main STHI are infections with Ascaris lumbricoides, Trichuris trichiura and hookworms. STHI have a significant effect on the growth and development of children. A national survey for STHI in El Salvador by Pan American Health Organization and Ministry of Health in 2012 in school children aged 8years to 10 years. The survey collected data on age, gender, behavioral habits, and source of drinking water, type of toilet facility used and ecological zone of residence. A) We did an analyses of the data with an aim to determine the prevalence of STHI in El Salvador, assess the risk factors and risk interactions. B) We also aimed to determine the efficacy of urea as a potential additive for inactivation of Ascaris suum in solar toilets. Methods: A) Data from 1310 subjects was analysed for determination of prevalence of STHI in El Salvador. Risk factor assessment was done by chi-square test, unadjusted logistic regression and fully adjusted logistic regression. Risk factor interactions was tested on multiplicative and additive scale. B) Urea was tested for efficacy in inactivation of Ascaris suum ova in 20 solar toilets. Under conditions of controlled pH and moisture, concentration of gas ammonia, peak temperature were measured along with duration of treatment with urea to determine viability of Ascaris suum samples placed in the solar toilets. Results: I) The prevalence of Ascaris lumbricoides in 8-10 year old school children is 2.75%, Trichuris trichiura is 4.1% and hookworm is 1.83%. A) For Ascaris lumbricoides infection: Significant risk in individuals from volcanic chains and central depression compared to those from the mountains. Spring or well water when used as source of drinking water was associated with higher risk of infection when compared with piped water. Higher infection was also associated with open air defecation compared to use of septic tank or flush toilet. Use of sandals or no footwear was associated with a higher risk of infection when compared to use of closed footwear at all times. B) For Trichuris infection: Coastal plains were associated with a higher risk of infection compared to the mountains while rural status was protective against infection. Spring or well water when used as source of drinking water was associated with higher risk of infection when compared with piped water. Use of sandals or no footwear was associated with a higher risk of infection when compared to use of closed footwear at all times. C) For hookworm infection: Risk of infection was higher in individuals from urban regions. Spring or well water when used as source of drinking water was associated with higher risk of infection when compared with piped water. Use of sandals or no footwear was associated with a higher risk of infection when compared to use of closed footwear at all times. Poor handwashing was shown to be protective against infection with hookworm. Significant risk factor interactions were identified for infection with each of the three soil transmitted helminths. II) Urea as an additive at 1%w/w to feces tested in solar toilets showed an inactivation rate of nearly half the Ascaris suum ova samples. Fifty percent or higher inactivation rates were associated with ammonia gas concentrations of 109.5 ppm or higher and duration of treatment of 72 hours or higher. Conclusions: Prevalence of STHI in 8-10 year old school children for 2012 in El Salvador is low. Significant risk factors for STHI in El Salvador are eco-epidemiologic zone, source of drinking water, type of sanitation, use of shoes behavior and urban status of place of residence. Use of urea for inactivation of soil transmitted helminth ova in feces is a possible intervention for environmental control of STHI.

Resumo: A degradação de cerca de 60 milhões de hectares de pastagens no Brasil afeta diretamente o estado nutricional dos rebanhos, conduzindo os pecuaristas a abrirem novas áreas de floresta, resultando em grave impacto de ordem econômica e ambienta!. A recuperação direta por meio da reposição dos nutrientes extraídos do solo ao longo dos anos representa menor risco ao produtor e reais possibilidades de adoção pela maior parte dos pecuaristas. Com este trabalho, objetivou-se avaliar os efeitos de nitrogênio (O, 100, 200, 300 e 400 kg/halano) com ou sem aplicação superficial de calcário nos atributos químicos de um Latossolo Vermelho distroférrico, nutrição mineral da planta, composição química, digestibilidade in vitro da matéria seca (DIVMS), características estruturais e massa de forragem de capim-Marandu. Foi utilizado um delineamento em blocos ao acaso em arranjo fatorial 2 X 5 com quatro repetições no esquema de parcela subdividida com medidas repetidas no tempo. A aplicação de calcário aumentou o pH e reduziu a acidez potencial nas camadas de O a 5 e 5 a 10 cm, 20 meses após aplicação, aumentou os teores de Ca e Mg, incrementou SB e a CTC na camada de O a 5 cm e saturação por bases nas camadas de O a 5 e 5 a 10 cm. O nitrogênio provocou acidificação do solo nos tratamentos sem calcário. O calcário aumentou a concentração de Ca nas lâminas foliares 11 meses após sua aplicação... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The degradation of 60 million hectares of pastures in Brazil directly affects the nutritional status os cattle herds drives farmers the open new forest areas resulting in great economic and environmental impact. The recovery through the replacement of nutrients extracted from the soil along the years represents lower risk to farmers and real possibilities of adoption by the majority of farmers. It was aimed at to evaluate the effects of nitrogen doses (O, 100, 200, 300 and 400 kg/ha of N by year) with or without surface liming on the chemical attributes of a red Latosol (Oxisol), plant mineral nutrition, chemical composition, "in vitro" digestibility, structural characteristic and herbage mass of Marandu-grass. The analysis of variance was performed based on a complete randomized block at factorial arrangement 2 X 5 with four replications design in a split-split-plot scheme with repeated measures over time. The lime increased the pH and reduced the acidity potential in the layers from O to 5 and 5 to 10 cm, increased the content of Ca, Mg, base sum and cation exchange capacity in the layer from O to 5 cm and base saturation in the layers from O to 5 and 5 to 10 cm. There was positive linear effect of N on the content of K in the layer from O to 5 cm of the soil and negative linear effect on the content of S in the soil layers from 10 to 20 and 20 to 30 cm of depth. There was positive linear effect of dose of N on the content of Ca, P, Mg and S during the summer months and negative linear effect on the same characteristics during the winter months. The content of N and K increased linearly to the increase of the doses of N in ali of months. In the months January and August there was quadratic effect of N doses on the leaf N content... (Complete abstract, click electronic access below)
Orientador: Ricardo de Andrade Reis
Coorientadora: Ana Cláudia Ruggieri
Banca: Valdo Rodrigues Haerling
Banca: Francisco Antonio Monteiro
Banca: Mauro Dal Secco de Oliveira
Banca: Ciniro Costa
Doutor

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
Urea is the most widely used nitrogen fertilizer in agriculture and its rapid hydrolysis in the soil can lead to significant losses by ammonia volatilization (N-NH3(g)) or by nitrate leaching (N-NO3 -). In order to reduce N losses emerged in the market several products represented by the slow or controlled release fertilizers and stabilized fertilizers. Work developed with traditional fertilizers that use monitoring of N-NH3(g) loss or losses as N-NO3 - do not provide direct information about the release rates and information about the N dynamics in soil. Usual methods of assessment coated fertilizers based on dissolution in water conditions differ greatly from those found in agricultural crops, especially by the influences of humidity, temperature, pH, microbial and enzymatic activity, organic matter and cation adsorption capacity of the soil. The dissolution of fertilizers and chemical reactions after the dissolution can print these changes in chemical characteristics of the soil solution, therefore the evaluation of the liquid phase of the soil can provide information regarding the release of nutrients from fertilizers. To evaluate the release of N in fertilized soil samples with coated ureas, we made two trials. In the first trial adaptations were made to collect soil solution (SS) by centrifugation method, we evaluated doses of N-urea (1 and 2 g kg-1), one treatment without N application and relative centrifugal force ( FCR: 1500, 2000, 2500, 3000 g). Collectors soil solution consisted of PVC pipe 70 mm in diameter, 100 mm high with one end closed. Inside the tube was placed a ring of PVC and this was placed on a perforated plate. The incubators were placed on the plate riddled during centrifugation. The incubators were constituted of recipient with a volume of 250 mL and perforated lid. Soil samples were kept inside incubators of pre-incubation to collect soil solution. The volume of the SS, pH, concentration of total-N and electrical conductivity (CE) were not affected by FCR used in the absence of fertilizer. The presence of fertilizers changed the SS volume collected, the CE and the content of total-N were also changed. The pH varied with FCR applied in treatments with dose 1 g kg-1, but was independent of the FCR with dose 2 g kg-1 (pH = 9,10). The dose 2 g kg-1 promoted the largest increase in the variables pH, N-total and CE. When applied 2 g kg-1 of N-urea the response curves for N-total and CE showed lower slope and higher volume collected with FCR of about 2500 g. In the second trial, the release of N from coated fertilizers and its dynamics in the soil solution and soil samples were evaluated in a soil of sandy loam texture, which received 2 g kg-1 of N-urea. After applying the fertilizer in the soil was incubated times ranging from 1 to 1296 h. To collect the SS used the component described above and FCR of 2500g. Additional treatments were maintained until 1530 h of incubation in them was collected weekly NH3 volatilization, used to estimate gaseous losses of N in the other treatments (1 to 1296 h). Also in these treatments was collected and the SS was evaluated soil where the concentration of different forms of N. The analysis procedures included the determination of N-urea, N-NH4 +, N-total and pH of the SS and soil. In the soil was determined concentrations of N-urea, N-NH4 + and N-total. The sum (N-total SS + Ntotal soil + N-NH3(g)) was assumed to be N released. The treatments were arranged in a factorial (7 + 1) x 9), seven fertilizer (U, UP1, UNBPT, USP2, USP3, USP4 and USP5), a control without nitrogen applied and nine incubation times ranging from 1 to 1296 h. Treatments were arranged in randomized blocks with four replications. The fertilizers were classified into three groups of different release patterns: G1 (U, UP1, UNBPT, averaging 94% of the N released until 64 h), G2 (USP2 and USP3, averaging 54% of N released up to 382 h) and G3 (USP4 and USP5, averaging 33% of the N released until 779 h). The dynamics of N in SS and soil was different between the groups, there were major transformations of urea-N to N-NH4 +, greater increases in pH and losses of N-NH3(g) for fertilizers G1 followed by those of G2 and G3. The maximum loss by volatilization (NVol) were on average 23% (G1, average time of 717 h), 15% (G2, average time of 1174 h) and 3% (G3, average time of 1296 h). The UNBPT was not effective in reducing losses NVol, but slowed in about three days the peak volatilization in relation to urea pearly. The UP1 was not effective in reducing N release and reduced losses of N-NH3(g). The soil solution analysis could differentiate fertilizers in relation to their ability to release N.
A ureia é o fertilizante nitrogenado mais utilizado na agricultura, e sua rápida hidrólise no solo pode levar a perdas expressivas de N por volatilização de amônia (N-NH3(g)) ou por lixiviação de nitrato (N-NO3 -). Com o objetivo de reduzir perdas de N, têm surgido no mercado produtos diferenciados, representados pelos fertilizantes revestidos de liberação controlada ou lenta, e fertilizantes estabilizados. Trabalhos desenvolvidos com os fertilizantes tradicionais que se utilizam do monitoramento das perdas de N-NH3(g) ou das perdas na forma de N-NO3 -, não oferecem informações diretas a respeito das taxas de liberação, ou mesmo informações sobre a dinâmica do N no solo. Métodos usuais de avaliação de fertilizantes revestidos baseados na dissolução em água diferem muito daquelas condições encontradas nos cultivos agrícolas, sobretudo pela influência da umidade, temperatura, pH, atividade microbiana e enzimática, matéria orgânica e CTC do solo. Processos de dissolução dos fertilizantes e reações químicas decorrentes podem imprimir mudanças nas características químicas da solução do solo, razão pela qual a avaliação da fase líquida deste pode oferecer informações da liberação de nutrientes dos fertilizantes. Para avaliar a liberação de N em amostras de solo fertilizadas com ureias revestidas foram realizados dois ensaios. No primeiro, adaptações para coleta de solução do solo (SS) pelo método de centrifugação foram feitas avaliando-se doses de N-ureia (1 e 2 g kg-1), além de um tratamento sem aplicação de N e força centrífuga relativa (FCR: 1500, 2000, 2500 e 3000 g). Os coletores de solução do solo foram constituídos de tubos de PVC de 70 mm de diâmetro e 100 mm de altura, com uma das extremidades fechada. Internamente, foi posicionado um anel de PVC, onde ficou apoiada uma placa crivada. Sobre a placa crivada, foi colocado durante a centrifugação, o incubador. Os incubadores foram constituídos de recipientes de plástico de 250 mL, com tampa crivada e cerca de 50 perfurações de 3,0 mm de diâmetro. Dentro dos incubadores foi acomodado o solo desde a fase de pré-incubação até a coleta da solução do solo. O volume da SS, o pH, a concentração de N-total e a condutividade elétrica (CE) não foram afetados pela FCR utilizada na ausência do fertilizante. A presença dos fertilizantes alterou o volume de SS coletado, bem como a CE e o teor de N-total. O pH variou com a FCR aplicada nos tratamentos com dose 1 g kg-1, porém foi independente de FCR na dose 2 g kg-1 (pH = 9,10). A dose 2 g kg-1 promoveu o maior incremento nas variáveis pH, N-total e CE da SS. Quando aplicados 2 g kg-1 de N-ureia as curvas de resposta para N-total e CE mostraram menor declividade e maior volume coletado próximo a 2500 g. No segundo ensaio, a liberação de N de fertilizantes revestidos e sua dinâmica na solução do solo e no solo foram avaliadas em amostras de um solo de textura franco-arenosa que recebeu 2 g kg-1 de N-ureia. Após a aplicação dos fertilizantes, o solo foi incubado em tempos que variaram de 1 até 1296 h. Para coleta da SS, utilizou-se o componente descrito anteriormente e FCR de 2500g. Tratamentos adicionais foram mantidos até 1530 h de incubação, neles foi coletada semanalmente a NH3 volatilizada, utilizada para estimar as perdas gasosas de N nos tempos de coleta da SS de 1 até 1296 h. Também nestes tratamentos coletou-se a SS e solo, onde avaliou-se a concentração das diferentes formas de N. Os procedimentos de análise incluíram a determinação de N-ureia, N-NH4 + e N-total na SS e no solo, bem como o pH da SS. O somatório (N-total da SS + Ntotal do solo + N-NH3(g)) foi assumido como N liberado. Os tratamentos foram arranjados em um fatorial (7+1) x 9), sendo sete fertilizantes (U, UP1, UNBPT, USP2, USP3, USP4 e USP5), um controle sem aplicação de N e nove tempos de incubação que variaram de 1 a 1296 h. Os tratamentos foram distribuídos em blocos casualizados com quatro repetições. Diante dos resultados, os fertilizantes foram classificados em três grupos de padrões de liberação distintos: G1 (U, UP1, UNBPT, com média de 94 % do N liberado até 64 h), G2 (USP2 e USP3, com média de 54 % do N liberado até 382 h) e G3 (USP4 e USP5, com média de 33 % do N liberado até 779 h). A dinâmica do N na SS e no solo foi diferente entre os grupos, observaram-se maiores transformações de N-ureia para N-NH4 +, maiores incrementos no pH e nas perdas de N-NH3(g) para fertilizantes do G1 seguidos daqueles do G2 e G3. As perdas máximas por volatilização N-NH3(g) foram em média de 23 % para o G1, 15 % para o G2 e 3 % para o G3. O fertilizante UP1 apresentou liberação de N e volatilização de NH3 similar a ureia perolada, mostrando a ineficiência do revestimento com o polímero. Os fertilizantes apresentaram padrões diferenciados de liberação de N, sendo possível avaliar essas diferenças por meio da análise química da solução do solo.

Thesis (M.S.)--University of North Carolina at Chapel Hill, 2007.
Title from electronic title page (viewed Apr. 25, 2008). "... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Environmental Science and Engineering." Discipline: Environmental Sciences and Engineering; Department/School: Public Health.

Les sols qui ne rencontrent pas les normes d’ingénierie civile doivent êtres soumis à des améliorations géotechniques car les vibrations causées par les tremblements de terre ou par la surcharge sur des infrastructures en hauteur peuvent mener à la liquéfaction partielle ou totale des sols saturés en eau. Ceci peut donc entrainer des dommages importants aux structures construites sur ces sols. Certaines méthodes existent pour remédier à ce problème, mais elles demeurent couteuses et parfois toxiques car elles utilisent de l’acrylamide et des lignosulfates. La bio-précipitation in situ de calcite dans les sols représente une méthode alternative. Le tout se fait avec des bactéries qui démontrent une activité uréolytique. La présente étude s’est intéressée à l’activité uréolytique des souches Escherichia coli, Sporosarcina ureae, Bacillus pasteurii, Lysinibacillus sphaericus, Bacillus subtilis et Bacillus megaterium. Les résultats démontrent que l’urée est seulement dégradée par les souches S. ureae et S. pasteurii. L’incubation de S. ureae en présence de Ni2+ (0.1-1 ppm) et Fe2+ (1-10 ppm) a toutefois permis d’augmenter l’activité catalytique de la souche, ce qui démontre l’importance des éléments nutritifs lors de l’hydrolyse de l’urée. Afin de tester l’activité uréolytique des autres souches, nous avons introduit un système d’expression uréase dans la souche E. coli en substituant des amino-acides dans la structure primaire des protéines. Suite à cette modification, l’activité uréolytique de E. coli s’est améliorée et est devenue comparable à celle des souches S. ureae et S. pasteurii. L’injection de S. ureae et du mutant E. coli dans des sables non-consolidés a permis de cimenter de façon significative (p < 0.05) le matériel par rapport à des sables non inoculés, et ce après seulement 48 heures. Le transfert du système recombinant de E coli vers S. ureae est présentement en cours. Ces résultats prometteurs indiquent qu’il est possible de stimuler la précipitation in situ de calcite en utilisant des bactéries et de stabiliser les sols prônes à la liquéfaction. === Soils often do not satisfy functional requirements for civil engineering projects and as a result geotechnical improvements to soils are often made. Dynamic shaking during earthquakes or static overloading by overlying structures may still result in liquefaction in partially or fully water saturated soils. These have little bearing capacity for structures. Severe damages can result. Moreover, preventative soil grouting strategies are expensive, toxic, and permanent due to acrylamides, lignosulfonates, and otherwise harmful compounds present therein. Alternative methods of strength enhancement are advisable. Microbial induced calcite precipitation (MICP) was assessed in this investigation to consolidate loose, sandy soils. Ureolytic activty of Escherichia coli, Sporosarcina ureae, Bacillus pasteurii, Lysinibacillus sphaericus, Bacillus subtilis and Bacillus megaterium were assessed. Urea was readily degraded foremost by S. ureae and next by S. pasteurii with no significant (p <0.05) activity in other strains. Incubation of S. ureae with 0.1 - 1ppm Ni2+ and 1-10ppm Fe2+ was shown to improve catalytic activity, suggesting their importance as a dietary source for urea hydrolysis. A urease expression system was established in E. coli and particular amino acid substitutions in protein primary structure made. Enhanced ureolytic activity was observed in these E. coli mutants, comparable to native S. ureae activity. Application of wild type S. ureae and recombinant E. coli for MICP in a model sand showed significant (p < 0.05) improvements compared to controls after 48 hours. Transfer of the recombinant system in E. coli to S. ureae is currently underway. These results provide valuable insight affirming that a practical system for the application of MICP may be feasible in the field for the strength enhancement of native and construction-laid loose, sandy soils.

Blends of controlled release and stabilized nitrogen (N) fertilizer represent an alternative to provide N at all corn growth stages, and is an option to reduce costs compared to the use of solely controlled release N. In this context, field experiments were conducted in Southeast Brazil with the use of a blend of polymer-sulfur coated urea (PSCU) and NBPT-treated urea (NBPTU) at a 70:30 ratio, applied at corn planting and incorporated into the soil. The objectives of the study were: i) to quantify and measure each fertilizer-derived N fate in the plants, and determine the nitrogen recovery efficiency of each N source in the blend; ii) to evaluate corn grain yield response to N rates (blend) in contrasting cropping systems, and to assess the posibility of reducing N rate when applying a blend of two enhanced efficiency N fertilizers compared to the application of regular urea; iii) understand and monitor changes in plant biomass and N uptake during the growing season. Fertilizer N contributed with less than 50% of the total plant N uptake at all evaluated corn growth stages (V4, V12, R2, and R6). At V4 growth stage, most of the N in the plant derived from fertilizer (NPDF) was provided by NBPTU, while later in the season, most of the NPDF was provided by PSCU. At harvest, most of the plant N was allocated in the grains (59%). Of the total plant N, 64% was supplied by the native soil N pool, 26% was provided by PSCU, and 10% by NBPTU. Therefore, NBPTU provided N to corn early in the season, while PSCU played a crucial role supplying N later in the season, as plants demand for N increased. Soil N was the main N source at all GS and this fraction decreased as N rate increased. At harvest, 64% of the total plant N was derived from the soil native N pool, 26% derived from PSCU, and 10% from urea. The measured fertilizer NRE of urea was in average 36%, and the estimated NUE from PSCU was 51%. In the second study, corn grain yield varied between sites, probably due to soil and climate characteristics of each site. Corn grain yield, N uptake, and biomass production were greatly impacted by fertilizer N. Grain yield and N uptake showed a quadratic response to N rates (blend). The blend of PSCU and NBPTU, applied at corn planting and incorporated into the soil proved to be a great strategy to attain yields at N rates below those needed when using regular urea. The third chapter focused on corn biomass and N uptake and partitioning throughout the growing season, and it was demonstrated that the amount of N uptake after flowering can reach up to 50% of the total plant N, thus, N availability must be guaranteed in late vegetative corn growth stages, and especially in the reproductive stages, which can be achieved by adopting enhanced efficiency N fertilizers such as the blend of PSCU and NBPTU used in this study.
A mistura de fertilizantes nitrogenados de liberação controlada e estabilizados representa uma alternativa para fornecer nitrogênio (N) em todos os estádios da cultura do milho, além de ser uma opção válida para reduzir custos em comparação ao uso exclusivo de produtos de liberação controlada. Neste sentido, conduziram-se experimentos de campo na região Sudeste do Brasil com a aplicação de um blend de ureia revestida com enxofre e polímeros (UREP) e ureia tratada com NBPT (U-NBPT), na proporção 70:30, aplicada na semeadura do milho, de forma incorporada. Os objetivos do trabalho foram: i) avaliar o destino do N dentro das plantas de milho proveniente dos fertilizantes misturados e determinar a eficiência de recuperação de cada um; ii) avaliar a resposta do rendimento de grãos de milho a doses de N (blend) em sistemas de produção contrastantes e avaliar a possibilidade de reduzir as doses de N quando aplicado o blend em comparação à ureia convencional; iii) entender e monitorar as mudanças da biomassa e o nitrogênio dentro das plantas de milho ao longo do ciclo da cultura. No primeiro estudo, o N na planta proveniente da UREP, da U-NBPT, e do solo (N-Solo) variaram ao longo do ciclo do milho. Contudo os fertilizantes nitrogenados contribuiram com menos de 50% do N total da planta em todos os estadios avaliados (V4, V12, R2 e R6). No estádio V4, a maior parte do N na planta proveniente de fertilizante (NPPF) foi fornecido pela U-NBPT, enquanto que nos estadios seguintes, a maior parte do NPPF foi fornecido pela UREP. O N-Solo foi o maior fornecedor de N para a planta, mas a contribuição diminuiu com o aumento das doses de N. Na colheita, 59% do total do N da planta foi alocado nos grãos. Do total de N da planta, 64% foi proveniente do N-Solo, 26% foi fornecido pela UREP, e 10% pela U-NBPT. A eficiência de recuperação da UREP e U-NBPT foram, respectivamente, 51 e 36%. No segundo estudo, o rendimento de grãos de milho variou entre locais, provavelmente devido às condições edafo-climáticas de cada área experimental. A aplicação do fertilizante nitrogenado influenciou o rendimento de grãos de milho, a produção de biomassa e acúmulo de N em todos os locais. O rendimento de grãos e acúmulo de N mostraram uma resposta quadrática às doses de N (blend). A incorporação do blend de UREP e U-NBPT na semeadura do milho mostrou-se como uma ótima estratégia para evitar perdas massivas de N e mostrou que pode atingir produtividade similar a ureia convencional com doses de N menores. O terceiro capítulo, com foco no acúmulo e particionamento da biomassa e N nas plantas de milho ao longo do ciclo, desmonstrou que a quantidade de N absorvido após o florescimento pode chegar a 50% do total de N acumulado nas plantas, pelo que adequada disponibilidade de N deve ser garantida nos estádios vegetativos finais e nos estádios reprodutivos da cultura do milho, o que pode ser conseguido com o uso de misturas de UREP e U-NBPT.

Orientador: Marcelo Carvalho Minhoto Teixeira Filho
Resumo: Alternative management practices are needed to minimize the need for chemical fertilizer use in non-leguminous cropping systems. The use of biological agents which can fix atmospheric nitrogen and promote plant growth has shown potential as an option to improve soil nutrient availability to grass crops. In recent years, studies investigating the effects of silicon (Si) have increased substantially, especially in grain crops. This increased interest in Si is likely due to the beneficial effects of Si application on plant resistance to abiotic and biotic stresses, reflecting on greater plant development. This research was developed to investigate if inoculation of corn and wheat with Azospirillum brasilense associated with Si can enhance nitrogen use efficiency (NUE) and improve plant nutrition and yield, leading to a greater economic profit. The study was set up in a Rhodic Haplustox under no-till system, located in Selvíria, state of Mato Grosso do Sul, Brazil. The field trial took place during the 2015/16 (November-March), 2016 (April-September), 2016/17 (November-March) and 2017 April-September) seasons, with corn and wheat crops in sucession (spring/summer and winter seasons for corn and wheat, respectively). Treatments were tested in a randomized completely block design with four replicates, arranged in a full factorial design 5 × 2 × 2 and included: i) five N application rates, as urea source, applied in side-dressing (0, 50, 100, 150 and 200 kg ha-1); ii) two liming sou... (Resumo completo, clicar acesso eletrônico abaixo)
Doutor

Orientador : Celso Aparecido Bertran
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Mestrado

The United Nations Millennium Development Goals have prioritized improving access to sanitation, but unfortunately about a third of the global population is still without an improved sanitation source and one billion still practice open defecation. Lack of access to adequate and safe sanitation means the proliferation of dangerous pathogens in the environment, especially soil-transmitted helminths (STHs). In the Bocas del Toro Province of Panama (and similar locations in the world), composting latrines have been built in many of the indigenous communities in the area. They are a form of dry or ecological sanitation and are designed to produce an end product that can be used as a soil amendment for agricultural purposes. The issue is that many of these latrines are not working as designed and do not go through the composting process. Instead, they may act as incubators for harmful pathogens, such as Ascaris lumbricoides (roundworm). This research 1) provides an extensive literature review of the health situation of Panama, focusing on indigenous populations; soil-transmitted helminths and helminthiasis; Ascaris lumbricoides and its implications for wastewater reuse and land application of biosolids/sewage sludge; and inactivation of Ascaris in composting latrines; and 2) develops and proposes an experimental plan, with field-based methods, to assess the inactivation of Ascaris, by urea and solar heat (increased temperature), in composting latrines in Panama. Various experiments have been conducted in the laboratory using urea and increased temperature to inactive Ascaris; however few have been carried out in dry toilet technologies in the field. The contribution of this thesis is the field-based experimental design developed for inactivating Ascaris in composting latrines. The methods build upon previous research carried out both in the laboratory and in the field.

La dynamique de l'azote a été suivie à l'aide de l'azote 15 dans les trois principaux sols de l'écosystème amazonien, un oxisol, un ultisol et un Gley peu humique (GHP). Les études ont été conduites en plein champ et sous conditions contrôlées. L'urée a été mieux utilisée que le sulfate d'ammonium. Dans les oxisols et ultisols cette supériorité est probablement due à l'augmentation du ph qui favoriserait l'activité des microorganismes du sol. L'engrais a contribué faiblement à la nutrition azotée des plantes par rapport à l'azote provenant du sol. Les apports d'engrais, principalement sous forme uréique et dans les sols acides, ont augmenté la minéralisation de l'azote organique du sol. Il y a eu dans ce cas, une interaction positive (ANI=added nitrogen interaction) entre l'azote de l'engrais et l'azote du sol. Après 60 jours d'incubation environ 60% de l'azote apporté par les engrais a été retrouve sous forme nh₄+ dans l'oxisol et l'ultisol, tandis que 50% de l'azote apporte a été minéralisé sous forme de no₃- dans le GPH. Par ailleurs, dans l'oxisol et l'ultisol on obtient avec l'incorporation de l'engrais vert caupi (vigna unguiculata l. ), une concentration en ions nh₄+ aussi élevée que celle observée en présence d'engrais minéraux; ceci montre le potentiel de ces légumineuses pour la fourniture d'azote dans ces sols acides. L'organisation biologique de l'engrais est également favorisée dans le cas de l'urée alors que les pertes sont toujours plus élevées en présence de sulfate d'ammonium que d'urée. Leur diminution devrait permettre une amélioration de l'efficience de ces engrais azotés. Sur un plan économique, le meilleur fertilisant à conseiller dans les écosystèmes amazoniens est l'urée

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A intensificação da produção dos animais em sistemas confinados gera uma alta produção de esterco bovino que pode contribuir para o fornecimento de nutrientes. Além de proporcionar melhorias em atributos químicos e físicos do solo. Diante deste contexto trabalhou-se com a hipótese de que o esterco bovino pode substituir total ou parcialmente o fertilizante nitrogenado industrial na adubação do capim-tifton 85. Assim, o objetivo com o presente trabalho foi avaliar o efeito da combinação nitrogênio x esterco da produção de capim-tifton 85 e em atributos químicos e físicos do solo. O experimento foi instalado durante os anos agrícolas 2013-2014 e 2014-2015. Os tratamentos consistiram de cinco doses de nitrogênio (N): 0, 50, 100, 200 e 300 kg ha-1, e cinco doses de esterco (E): 0, 10, 20, 40 e 60 Mg ha-1 combinadas em esquema fatorial. As doses de 300 kg ha-1 de N e 40 Mg ha-1 de E proporcionaram a maior produção de massa seca (10.469 kg ha-1) e altura (75,10 cm) em 2013-14. A associação das maiores doses de esterco e nitrogênio resultaram em melhor desempenho da forrageira em relação a produção de massa seca total (13.305 kg ha-1). Houve aumento de 71 e 88% de acúmulo de nitrogênio no capim-tifton 85 no ano agrícola 2013-14 e, aumento de 126 e 163 em 2014-15, com o uso de esterco e de N-ureia, respectivamente. A recuperação aparente de N com o uso de esterco foi maior no segundo ano de avaliação. Com o uso de N-ureia não houve variação nos teores de carbono orgânico do solo e nas formas de carbono associadas aos minerais e particulada. O uso de 60 Mg ha-1 de esterco por dois anos consecutivos aumentou a estabilidade (94,96%) e o diâmetro médio ponderado dos agregados (4,86 mm), e diminuiu a resistência do solo à penetração (0,99 Mpa), devido ao aumento de 35% no teor de carbono do solo.
Intensified production of animals in confined systems generates a high production of cattle manure that can contribute to the nutrient supply. In addition to providing improvements in soil chemical and physical attributes. In this context, we worked with the hypothesis that bovine manure can totally or partially replace industrial nitrogen fertilizer in fertilization of tifton grass 85. Thus, the objective with the present work was to evaluate the effect of the nitrogen and manure combination of tifton 85 grass production and on soil chemical and physical attributes. The experiment was installed during the agricultural years 2013-2014 and 2014-2015. The treatments consisted of five doses of nitrogen (N): 0, 50, 100, 200 and 300 kg ha-1, and five manure doses (E): 0, 10, 20, 40 and 60 Mg ha-1 combined in factorial scheme. The doses of 300 kg ha-1 of N and 40 Mg ha-1 of E provided the highest dry mass production (10,469 kg ha-1) and height (75,10 cm) in 2013-14. The association of the highest doses of manure and nitrogen resulted in better forage performance in relation to the production of total dry mass (13,305 kg ha-1). There was an increase of 71 and 88% of nitrogen accumulation in Tifton 85 grass in the agricultural year 2013-14 and, increased 126 and 163 in 2014-15, respectively. The apparent recovery of N with use of manure was greater in the second year of evaluation. With the use of N-urea, there was no change in soil organic carbon and forms of carbon associated with minerals and particulate. The use of 60 Mg ha-1 of manure for two consecutive years increased the stability (94.96%) and the weighted average diameter of the aggregates (4.86 mm) and decreased soil resistance to penetration (0.99 MPa) due to the 35% increase in soil carbon content.

To date, there has been little research into the role of microbial community structure in the functioning of the soil ecosystem and on the links between microbial biomass size, microbial activity and key soil processes that drive nutrient availability. The maintenance of structural and functional diversity of the soil microbial community is essential to ensure the sustainability of agricultural production systems. Soils of the same type with similar fertility that had been under long-term organic and conventional crop management in Canterbury, New Zealand, were selected to investigate relationships between microbial community composition, function and potential environmental impacts. The effects of different fertilisation strategies on soil biology and nitrogen (N) dynamics were investigated under field (farm site comparison), semi-controlled (lysimeter study) and controlled (incubation experiments) conditions by determining soil microbial biomass carbon (C) and N, enzyme activities (dehydrogenase, arginine deaminase, fluorescein diacetate hydrolysis), microbial community structure (denaturing gradient gel electrophoresis following PCR amplification of 16S and 18S rDNA fragments using selected primer sets) and N dynamics (mineralisation and leaching). The farm site comparison revealed distinct differences between the soils in microbial community structure, microbial biomass C (conventional>organic) and arginine deaminase activity (organic>conventional). In the lysimeter study, the soils were subjected to the same crop rotation (barley (Hordeum vulgare L.), maize (Zea mais L.), rape (Brassica napus L. ssp. oleifera (Moench)) plus a lupin green manure (Lupinus angustifolius L.) and two fertiliser regimes (following common organic and conventional practice). Soil biological properties, microbial community structure and mineral N leaching losses were determined over 2½ years. Differences in mineral leaching losses were not significant between treatments (total organic management: 24.2 kg N ha⁻¹; conventional management: 28.6 kg N ha⁻¹). Crop rotation and plant type had a larger influence on the microbial biomass, activity and community structure than fertilisation. Initial differences between soils decreased over time for most biological soil properties, while they persisted for the enzyme activities (e.g. dehydrogenase activity: 4.0 and 2.9 µg g⁻¹ h⁻¹ for organic and conventional management history, respectively). A lack of consistent positive links between enzyme activities and microbial biomass size indicated that similarly sized and structured microbial communities can express varying rates of activity. In two successive incubation experiments, the soils were amended with different rates of a lupin green manure (4 or 8t dry matter ha⁻¹), and different forms of N at 100 kg ha⁻¹ (urea and lupin) and incubated for 3 months. Samples were taken periodically, and in addition to soil biological properties and community structure, gross N mineralisation was determined. The form of N had a strong effect on microbial soil properties. Organic amendment resulted in a 2 to 5-fold increase in microbial biomass and enzyme activities, while microbial community structure was influenced by the addition or lack of C or N substrate. Correlation analyses suggested treatment-related differences in nutrient availability, microbial structural diversity (species richness or evenness) and physiological properties of the microbial community. The findings of this thesis showed that using green manures and crop rotations improved soil biology in both production systems, that no relationships existed between microbial structure, enzyme activities and N mineralisation, and that enzyme activities and microbial community structure are more closely associated with inherent soil and environmental factors, which makes them less useful as early indicators of changes in soil quality.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
A degradação de cerca de 60 milhões de hectares de pastagens no Brasil afeta diretamente o estado nutricional dos rebanhos, conduzindo os pecuaristas a abrirem novas áreas de floresta, resultando em grave impacto de ordem econômica e ambienta!. A recuperação direta por meio da reposição dos nutrientes extraídos do solo ao longo dos anos representa menor risco ao produtor e reais possibilidades de adoção pela maior parte dos pecuaristas. Com este trabalho, objetivou-se avaliar os efeitos de nitrogênio (O, 100, 200, 300 e 400 kg/halano) com ou sem aplicação superficial de calcário nos atributos químicos de um Latossolo Vermelho distroférrico, nutrição mineral da planta, composição química, digestibilidade in vitro da matéria seca (DIVMS), características estruturais e massa de forragem de capim-Marandu. Foi utilizado um delineamento em blocos ao acaso em arranjo fatorial 2 X 5 com quatro repetições no esquema de parcela subdividida com medidas repetidas no tempo. A aplicação de calcário aumentou o pH e reduziu a acidez potencial nas camadas de O a 5 e 5 a 10 cm, 20 meses após aplicação, aumentou os teores de Ca e Mg, incrementou SB e a CTC na camada de O a 5 cm e saturação por bases nas camadas de O a 5 e 5 a 10 cm. O nitrogênio provocou acidificação do solo nos tratamentos sem calcário. O calcário aumentou a concentração de Ca nas lâminas foliares 11 meses após sua aplicação...
The degradation of 60 million hectares of pastures in Brazil directly affects the nutritional status os cattle herds drives farmers the open new forest areas resulting in great economic and environmental impact. The recovery through the replacement of nutrients extracted from the soil along the years represents lower risk to farmers and real possibilities of adoption by the majority of farmers. It was aimed at to evaluate the effects of nitrogen doses (O, 100, 200, 300 and 400 kg/ha of N by year) with or without surface liming on the chemical attributes of a red Latosol (Oxisol), plant mineral nutrition, chemical composition, in vitro digestibility, structural characteristic and herbage mass of Marandu-grass. The analysis of variance was performed based on a complete randomized block at factorial arrangement 2 X 5 with four replications design in a split-split-plot scheme with repeated measures over time. The lime increased the pH and reduced the acidity potential in the layers from O to 5 and 5 to 10 cm, increased the content of Ca, Mg, base sum and cation exchange capacity in the layer from O to 5 cm and base saturation in the layers from O to 5 and 5 to 10 cm. There was positive linear effect of N on the content of K in the layer from O to 5 cm of the soil and negative linear effect on the content of S in the soil layers from 10 to 20 and 20 to 30 cm of depth. There was positive linear effect of dose of N on the content of Ca, P, Mg and S during the summer months and negative linear effect on the same characteristics during the winter months. The content of N and K increased linearly to the increase of the doses of N in ali of months. In the months January and August there was quadratic effect of N doses on the leaf N content... (Complete abstract, click electronic access below)

Orientador: Mara Cristina Pessôa da Cruz
Coorientador: Edson Luiz Mendes Coutinho
Banca: Felipe Batistella Filho
Banca: Flávia Fernanda Simili
Banca: José carlos Barbosa
Banca: Itamar Andrioli
Resumo: A intensificação da produção dos animais em sistemas confinados gera uma alta produção de esterco bovino que pode contribuir para o fornecimento de nutrientes. Além de proporcionar melhorias em atributos químicos e físicos do solo. Diante deste contexto trabalhou-se com a hipótese de que o esterco bovino pode substituir total ou parcialmente o fertilizante nitrogenado industrial na adubação do capim-tifton 85. Assim, o objetivo com o presente trabalho foi avaliar o efeito da combinação nitrogênio x esterco da produção de capim-tifton 85 e em atributos químicos e físicos do solo. O experimento foi instalado durante os anos agrícolas 2013-2014 e 2014-2015. Os tratamentos consistiram de cinco doses de nitrogênio (N): 0, 50, 100, 200 e 300 kg ha-1, e cinco doses de esterco (E): 0, 10, 20, 40 e 60 Mg ha-1 combinadas em esquema fatorial. As doses de 300 kg ha-1 de N e 40 Mg ha-1 de E proporcionaram a maior produção de massa seca (10.469 kg ha-1) e altura (75,10 cm) em 2013-14. A associação das maiores doses de esterco e nitrogênio resultaram em melhor desempenho da forrageira em relação a produção de massa seca total (13.305 kg ha-1). Houve aumento de 71 e 88% de acúmulo de nitrogênio no capim-tifton 85 no ano agrícola 2013-14 e, aumento de 126 e 163 em 2014-15, com o uso de esterco e de N-ureia, respectivamente. A recuperação aparente de N com o uso de esterco foi maior no segundo ano de avaliação. Com o uso de N-ureia não houve variação nos teores de carbono orgânico do solo e na... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Intensified production of animals in confined systems generates a high production of cattle manure that can contribute to the nutrient supply. In addition to providing improvements in soil chemical and physical attributes. In this context, we worked with the hypothesis that bovine manure can totally or partially replace industrial nitrogen fertilizer in fertilization of tifton grass 85. Thus, the objective with the present work was to evaluate the effect of the nitrogen and manure combination of tifton 85 grass production and on soil chemical and physical attributes. The experiment was installed during the agricultural years 2013-2014 and 2014-2015. The treatments consisted of five doses of nitrogen (N): 0, 50, 100, 200 and 300 kg ha-1, and five manure doses (E): 0, 10, 20, 40 and 60 Mg ha-1 combined in factorial scheme. The doses of 300 kg ha-1 of N and 40 Mg ha-1 of E provided the highest dry mass production (10,469 kg ha-1) and height (75,10 cm) in 2013-14. The association of the highest doses of manure and nitrogen resulted in better forage performance in relation to the production of total dry mass (13,305 kg ha-1). There was an increase of 71 and 88% of nitrogen accumulation in Tifton 85 grass in the agricultural year 2013-14 and, increased 126 and 163 in 2014-15, respectively. The apparent recovery of N with use of manure was greater in the second year of evaluation. With the use of N-urea, there was no change in soil organic carbon and forms of carbon associated with minerals and particulate. The use of 60 Mg ha-1 of manure for two consecutive years increased the stability (94.96%) and the weighted average diameter of the aggregates (4.86 mm) and decreased soil resistance to penetration (0.99 MPa) due to the 35% increase in soil carbon content.
Doutor

O nitrogênio é o nutriente absorvido em maior quantidade pelo milho, o de maior custo e influencia diretamente na resposta da cultura em produtividade de grãos, sendo a uréia o fertilizante mais utilizado na agricultura brasileira; entretanto, o manejo inadequado do nitrogênio pode trazer sérios problemas de poluição para o ambiente. Os objetivos do presente trabalho foram: (a) verificar a potencialidade de poluição por nitrato em áreas de várzea cultivadas com milho com diferentes doses de nitrogênio, na forma de uréia; (b) quantificar o efeito das flutuações do lençol freático e das doses de nitrogênio na produtividade da cultura relativa de milho; e (c) verificar o efeito do nitrogênio nos componentes da planta e produção do milho. O experimento foi desenvolvido na Escola Superior de Agricultura “Luiz de Queiroz”, Universidade de São Paulo, em Piracicaba-SP. O sistema de drenagem foi constituído por 19 drenos subterrâneos de 45 m, espaçados de 10 m. Utilizou-se um delineamento experimental de blocos casualizados, com cinco tratamentos (0; 50; 100; 150 e 200 kg ha-1 de N) e três repetições. Cada parcela possuía um dreno subterrâneo e um poço de observação. Foram realizados monitoramentos de nitrato, avaliações fenológicas, concentração de N na folha de milho, produção de milho e seus componentes. A precipitação pluvial registrada no período foi de 562 mm. Concluiu-se que a adubação nitrogenada não afetou a qualidade de água nas descargas dos drenos por nitrato; que o índice de estresse (SEW30) respondeu de forma linear crescente às produtividades relativas dos grãos de milho revelando que as flutuações do lençol freático, em função das chuvas, ao longo do ciclo da cultura, contribuíram para o aumento da produtividade de grãos da cultura de milho; que a aplicação de nitrogênio em dose crescente proporcionou aumento de forma linear e positivo para os parâmetros de teor de nitrogênio total na folha e nos grãos; que houve resposta quadrática às doses crescentes de nitrogênio para altura de planta e de inserção de espiga de milho; produtividade de grãos (13% de teor de água); massa de matéria seca da palhada de milho e brácteas; número de grãos por espiga e número de grãos por fileira.
The nitrogen is the nutrient mostly absorbed by corn, being largest cost and which best responds to grain productivity. The urea is mostly used the fertilizer in Brazilian agriculture and inadequate nitrogen management practices can bring serious pollution problems to the environment. The objectives of the present work were: (a) to verify the pollution potentiality for nitrate in low land cultivated with corn with different nitrogen rates, in the urea form; (b) to quantify the effect of the water table fluctuation and nitrogen rates in the relative productivity of the corn crop; and (c) to verify the nitrogen effect on plant components and corn yield. The field experiment was carried out at Escola Superior de Agricultura "Luiz de Queiroz", University of São Paulo, in São Paulo state, Brazil. The drainage system consisted of 15 underground drains of 45 m, 10 m spaced. The experimental design consisted of complete randomized blocks with five treatments (0; 50; 100; 150 and 200 kg ha-1 N) and three replications. Each plot had an underground drain and an observation well. Drainage nitrate concentration was accomplished, phenological evaluation, nitrogen concentration in the corn leaves, corn yield and its components, were done. The registered rainfall in the period was 562 mm. It was concluded that the application of nitrogen did not affect water quality in drain discharges in relation to nitrate; the stress index (SEW30) responded in a growing linear way for the relative grain corn productivities, showing that water table fluctuations due to rainfall, during the crop cycle, contributed to increase corn productivity; nitrogen application in growing rates lead to a linear and positive increase of nitrogen content in leaf and grain; a quadratic response to growing nitrogen rates was found in relation to plant height and corn cob insertion; grain yield (13% moisture); straw dry mass; dry mass of husk; number of grains per corn cob and number of grains per row.

Notre objectif était d'étudier la rétention d'herbicides de la famille des phenylurées sur des adsorbants minéraux et dans le sol. Les molécules retenues sont le chloroxuron, le chlortoluron, le metobromuron, l'isoproturon et le difenoxuron. Les adsorbants utilises sont la celite, le florisil, l'alumine, le carbonate et le sulfate de calcium. Les sols étudiés sont un sol limoneux-argileux et un sol limoneux-sableux. Nous poursuivons le double but analytique et environnemental d'améliorer les étapes de purification par chromatographie d'adsorption d'extraits en vue de l'analyse de résidus, et de prévoir leur dispersion dans le sol, leur diffusion en direction des nappes et leur exposition à la dégradation microbienne. La méthode suivie passe essentiellement par le tracé de cinétiques et d'isothermes d'adsorption-désorption, et de courbes de mobilité en présence d'eau ; les variations de concentrations des urées dans la phase liquide ont été mesurées par HPLC-UV. Les isothermes ont été modélisées dans les formalismes de Freundlich, Langmuir et Temkin. Les influences sur la mobilité des urées dans des colonnes de sol, de la concentration saline de la phase aqueuse (cacl#2) et de formulants tensio-actifs (polyphénols ethoxyles) ont été évaluées par la même méthodologie. Ces études ont été complétées par l'examen de spectres IR pour caractériser les groupes structuraux de ces molécules engagés dans leur liaison avec les adsorbants. Nous mettons en évidence le rôle privilégié des groupes phenoxy dans l'adsorption sur le florisil ; des effets hydrophobes dus à la substitution des noyaux aromatiques par le chlore pourraient être à l'origine de la rétention du chloroxuron et du chlortoluron sur tous les adsorbants, et la combinaison d'effets stériques dus à la taille du brome, d'effets électroniques et dipolaires dus au groupe methoxy sur la fonction urée pourraient intervenir dans la faible rétention du metobromuron sur tous les adsorbants. Enfin parmi les formulants étudiés, seul le soprophor FL à une concentration supérieure à 0,05 g/l a un effet accélérateur marqué sur la mobilité de l'isoproturon en colonnes de sol.

Apesar de o manejo da pastagem ser um componente chave em sistemas pastoris, poucos esforços foram feitos para determinar a intensidade de pastejo adequada para pastagens tropicais, especialmente sob condições irrigadas. O atrativo econômico de sistemas de pastagens irrigadas depende da elevada produtividade da pastagem, o que significa que fertilizantes nitrogenados precisam ser utilizados. Entretanto, para estabelecer medidas efetivas visando o manejo do nitrogênio (N) é necessário entender o balanço entre entradas e saídas de N e a eficiência de ciclagem e transformações do N em sistemas de produção animal em pastejo. Nesse contexto, sete experimentos foram realizados para avaliar o efeito do resíduo pós-pastejo ou de níveis de fertilizante nitrogenado sobre a produção de forragem e a recuperação do N-fertilizante em pastagem irrigada de Panicum maximum cv. Tanzânia. O resíduo pós-pastejo para pastagem de capim Tanzânia irrigada e adubada com N durante o inverno, considerando ciclo de pastejo de 36 dias, deve ser de aproximadamente 1.900 a 2.100 kg/ha de massa seca verde. Para as estações de primavera e verão, a massa de forragem residual deve ser de cerca de 1.700 a 2.700 kg/ha de massa seca verde. Esse manejo assegurou que a produção de folhas e a relação folha/haste fossem próximas do máximo. Parcelas de 1 m 2 , tendo uma touceira do capim em seu centro geométrico, foram adequadas para estudar a recuperação de fertilizante- 15 N, independentemente da intensidade de pastejo e estação do ano. O aumento da intensidade de pastejo resultou em decréscimo na massa da touceira. Quanto menor a massa da touceira, maior a dependência no N-fertilizante. A combinação de elevada umidade do solo, ausência de chuva no dia subseqüente à adubação e alta temperatura determinaram baixa recuperação de 15 N-uréia no sistema solo-planta (< 35% do N aplicado) e elevadas perdas de amônia por volatilização (> 40% do N aplicado) nos níveis de adubação superiores a 80 kg/ha de N durante o verão. A absorção foliar da amônia volatilizada da uréia aplicada ao solo variou de 2,5% (120 kg/ha de N) a 16,4% (40 kg/ha de N) do nitrogênio volatilizado. Com adubações inferiores a 60 kg/ha de N observou-se níveis subótimos de nutrição nitrogenada e tendência de maior discriminação do 13 C durante o verão.
Whilst grazing management is a key component in pastoral systems little effort has been made to determine the adequate grazing intensity for tropical pastures, especially under irrigated conditions. The economical attractiveness of irrigated pasture systems depends on high pasture productivity, meaning that fertilizer nitrogen (N) must be used. However, to make effective changes toward sustainable N management, an understanding of the balance between N inputs and outputs and the efficiency of N cycling and transformation within the grassland system is required. In this context, seven experiments were carried out to evaluate the effect of post-grazing residue or nitrogenous fertilizer levels on herbage production and on fertilizer-N recovery in irrigated Panicum maximum cv. Tanzania pasture. The post-grazing residue for irrigated, N-fertilized Tanzania grass pasture during the winter, considering a 36-day grazing cycle, should be around 1900 to 2100 kg/ha of green dry matter. During the spring/summer seasons the residual stubble mass should be around 1700 to 2700 kg/ha of green dry matter. This management ensured that leaf production and leaf/stem ratio were close to the maximum. A plot-size of 1 m 2 , with a tussock of the grass in its geometric center, was adequate to study 15 N-fertilizer recovery irrespective of grazing intensity and season of the year. Increasing the grazing intensity resulted in decreased tussock mass. The smaller the tussock mass the greater was the reliance on fertilizer-N. The combination of high soil water content, lack of rainfall in the day following fertilization and high temperature determined low urea- 15 N recovery in the soil-plant system (< 35% of applied N) and high ammonia volatilization losses (> 40% of applied N) at fertilizations levels higher than 80 kg N/ha during the summer. The absorption of ammonia volatilized from urea applied to soil varied from 2.5% (120 kg N/ha) to 16.4% (40 kg N/ha) of the volatilized nitrogen. With fertilizations lower than 60 kg N/ha it was observed sub-optimal N nutrition and a trend of higher 13 C discrimination during the summer.

The effect of organic and mineral fertilizers on biological activity of different genesis soils in long-term crop rotation trials was determined. Biological activity was diverse in the soils of different genesis and it activity correlated with some soil chemical properties. Organic and mineral fertilizers and their combinations more increased biological activity in the soil than only mineral fertilizers. Mineral fertilizers suppressed dehydrogenase and alkaline phosphatase activity (180 kg ha-1) with phosphorus and potassium fertilizers. The relationship between the crops grown, their yield and enzyme activity and respiration intensity in the soil was investigated.

博士
國立臺灣大學
農業化學研究所
99
Organic fertilizers are necessary to sustain soils ability to crop production and to help reduce environmental pollution especially due to nitrogen (N) and phosphorus (P) leaching. But heavy application of these in excess of crop needs can buildup N and P levels in soil affecting soil and water quality. Composted manure is known as an environmentally safer organic fertilizer but leaching and crop recovery from composted manure applied soils is less well understood and this knowledge could help managing compost application in high rainfall areas. A green-house experiment conducted at the National Taiwan University, Taipei from April 2006 to June 2008 evaluated the effects of compost and urea combinations on dry matter yields (DMY), apparent crop recovery of N and P, residual effects on soil and changes in soil quality. Treatments consisted of urea (F250), compost (M250), and combination of these two (F125M125) –all supplied 250 kg N ha-1 while two others (M500 and F250M250) doubled the N supply and an untreated Control (Ctrl) for comparison. M125, M250 and M500 corresponded to 8, 16 and 32 Mg ha-1 of composted manure application, respectively. Cabbage (Brassica oleracea L.) and corn (Zea mays L.) crops were grown in standard Wagner pots in annual rotation using 12.9 kg (dry weight basis) of acid sandy clay loam soil. Soils were leached fortnightly applying 80 and 60 mm of water to cabbage and corn corresponding to 2000 and 1500 mm average annual rainfall, respectively. Leaching of mineral N (MNL) and inorganic water soluble P (WSP) were monitored in leachate water samples during growing seasons for a total of 28 times in 2-y. Although composted manure application was not repeated, blanket of NPK fertilizers were applied to all treatments except the Ctrl from crop2 to crop4 seasons from mineral sources in order to help maintain normal growth of the test crops. With some variations among treatments, increasing rate of N application from 0 to 500 kg ha-1 mostly increased DMY of cabbage and corn. A tendency of high compost (M500) favoring cabbage DMY, and corn DMY indifferent of urea/compost combination was apparent in both years probably due to the effects of crop-rotation and physiological differences between crops. Demerit of high MNL outweighed the merit of high crop N recovery in urea treatment (F250). Apparent crop N recoveries were higher in urea and compost combined treatments in 4 of 4 crops. But there were outstanding results from higher compost additions such as the large reductions in MNL due to reduced volume of leachate outflows, greater utilization of water for higher crop growth, as well as higher N and P retention and addition of organic carbon in soil. An annual application or higher compost rate appears useful to increase soil pH and nutrient availability. Although inorganic WSP leaching was not high, the results suggested the need to evaluate other forms of P leaching such as total P and algal P from this compost applied soil. The assumptions of 50% N mineralization and 30% P release rates in this compost could not be substantiated. The results implied that nutrient management goal in agriculture would be more realistic if N and P credits in this compost are considered to be approximately 25% and 15%, respectively for the 1st-y of application. Over assumption partly explained why crop DMY were relatively low in this study compared with other pot studies that did not involve leaching operations. Use of soil management assessment tool for deriving soil quality index (SQI) did not show statistical differences among compost and urea treatments. However, the tool was found useful because SQI correlated with DMY in 4 of 4 crops. Taken soil, leachate, and crop parameters together, evidences show that an application of 32 Mg ha-1 of compost outperformed all other treatments although combined application of compost (16 Mg ha-1) with urea (250 kg ha-1) was the best candidate for apparent crop recovery of N and P and MNL. The results of this pot study were found consistent and encouraging; however a field-scale study would be helpful to validate these conclusions.

In the present thesis, implications of pasture establishment, fertilization and abandonment on soil C and nutrient dynamics were investigated for the mountain rainforest region of southern Ecuador. Over the past decades the natural forest of the study area has been threatened by conversion to cattle pastures. However, the soil fertility of these extensively grazed pastures (active pastures) declines continuously during pasture use. The invasion of bracken fern (Pteridium arachnoideum) leads to pasture abandonment when bracken becomes dominant. In order to reveal the mechanisms behind the deterioration of soil fertility, biotic and abiotic soil properties and their interaction were analyzed along a land‐use gradient (natural forest – active pasture – abandoned pasture). The ecosystem disturbance of the mountain rainforest through pasture use changed the microbial function and structure, and affected soil CO2‐C fluxes. Annually, 2 Mg soil CO2‐C ha‐1 were additionally emitted from the pasture land. This acceleration in soil respiration rates was related to accelerated rates of microbial C mineralization and fine‐root respiration. The high‐quality, N‐rich above‐ and belowground residues of the pasture grass (S. sphacelata, C4‐plant), especially the huge fine‐root biomass, provided a high C and N availability for soil microbes. Compared to the forest, increased soil pH and accelerated base saturation were further factors beneficial for soil microbial growth and metabolism of the upper mineral soil at active pastures. Three times higher amounts of microbial biomass C and a significant shift in the microbial community structure towards a higher relative abundance of Gram(‐)‐ bacteria and fungi were observed. Long‐term pasture use and the invasion of bracken (C3‐plant) diminished beneficial effects for microbes, causing a significant decrease in the C, net, and gross N mineralization rates as well as a two‐third reduction in the microbial biomass. A preferential substrate utilization of grass‐derived C4 by the soil microbes resulted in a rapid decline of the C4‐pool. As a consequence, the less available C3‐pool from bracken and former forest increased its dominance in the SOC‐pool, further decreasing pasture productivity and finally causing pasture abandonment. The lower quality and quantity of above‐ and belowground residues of the bracken (high lignin content, C/N) resulted in resource‐limited conditions that influenced the microbial function to greater extent than their structure. The microbial structure seemed to be sensitive mainly to soil pH along the land‐use gradient. Thus, a disconnection between microbial structure and function was identified. Fertilization experiments were conducted both in the lab and in the field to evaluate the impact of urea and/or rock phosphate amendment on SOM dynamics and on pasture productivity of active pastures. After combined fertilization the pasture yield was most efficiently increased by 2 Mg ha−1 a−1, indicating a NP‐limitation of grass growth. Furthermore, the fodder quality was improved by a higher content of P and Ca in the grass biomass. The microorganisms of the active pasture soil responded with an adaptation of their structure to the increased substrate availability in the short term, but did not change their initial functions in the long term. After urea/ rock phosphate addition a significant increase in the relative fungal abundance was detected, but neither a microbial limitation of energy nor of N or P was observed. However, urea addition accelerated gaseous losses of soil CO2‐C in the short term. In the study area, pronounced alterations in ecosystem functioning due to land‐use changes were detected, especially in soil C and N cycling rates. For a sustainable land‐use in this region it is crucial to prevent pasture degradation and to rehabilitate degraded pastures in order to protect the prevailing mountain rainforest ecosystem. It is of crucial importance for active pasture soils to maintain or even increase resource availability, being one indicator of soil fertility. In this context, the soil organic matter has to be retained in the long‐term to maintain high microbial activity and biomass, and thus pasture productivity. A moderate fertilization with urea and rock phosphate can be a first step to provide continuous nutrient supply for grass growth and to strengthen livestock health through increased fodder quality. However, the risk of further additional emissions of soil CO2‐C due to increased loads of urea fertilizer application has to be kept in mind. Overall, for the establishment of a sustainable land‐use management the control of bracken invasion and an adjusted nutrient management are needed. Further investigations on the reduction of soil nutrient losses and increased nutrient use efficiencies of plants, such as combined planting with legumes or the usage of cultivars with special nutrient acquisition strategies, should be in the focus of future work.:Contents Acknowledgement I Table of content III List of Tables V List of Figures VI Abbreviations VII Summary (English/German/Spanish) .................................................... 1 1 Introduction ................................................................................... 6 1.1 Impact of land‐use changes on C and nutrient dynamics ............... 6 1.1.1 Soil organic carbon and soil CO2 flux 7 1.1.2 The role of soil microbes 8 1.1.3 Plant‐microbe interactions 10 1.1.4 Impact of soil environment on soil microbes 11 1.2 Pasture establishment in the tropics .......................................... 13 1.3 Research area ....................................................................... .... 15 2 Objectives and research questions ......................... ................... 19 2.1 Land‐use change ........................................................................ 19 2.2 Pasture management ............................................................. ... 21 3 Methodology ................................................................................. 22 3.1 Study sites ............................................................................... 22 3.1.1 Land‐use gradient 22 3.1.2 Pasture Fertilization Experiment (FERPAST) 23 3.2 General analyses ....................................................................... 24 3.2.1 Laboratory experiments 25 3.2.2 In situ measurements 26 3.2.3 Statistics 27 4 Results ............................................................................................ 28 4.1 Soil C and nutrient dynamics along a land‐use gradient ............. 28 Potthast, K., Hamer, U., Makeschin, F., 2011. Land‐use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling. Biogeochemistry, 1‐17. 4.2 Impact of pH and ongoing succession on microbial function and structure .......... 29 4.3 Response of soil microbes to bracken‐invasion ........................... 32 Potthast K., Hamer U., Makeschin F. 2010. Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador. Soil Biology and Biochemistry 42, 56‐64. 4.4 Response of soil microbes and pasture grass to fertilization ........33 Hamer, U., Potthast, K., Makeschin, F., 2009. Urea fertilisation affected soil organic matter dynamics and microbial community structure in pasture soils of Southern Ecuador. Applied Soil Ecology 43, 226‐233. Potthast, K., Hamer, U., Makeschin, F., 2012. In an Ecuadorian pasture soil the growth of Setaria sphacelata, but not of soil microorganisms, is co‐limited by N and P. Applied Soil Ecology 62, 103‐114. 5 Discussion .................................................................................... 34 5.1 Impact of land‐use changes ...................................................... 34 5.1.1 Soil CO2 fluxes 34 5.1.2 Microbial structure and function 34 5.2 Soil fertility loss of pastures ‐reasons and first prevention steps‐ . 37 5.2.1 Litter decay and SOM dynamics 37 5.2.2 Fertilization and SOM dynamics 39 5.3 Conclusions and Perspectives ...................................................... 42 References ..................................................................................... 46 Curriculum vitae......................................................................... 58
In der vorliegenden Dissertation werden die Auswirkungen der Weideetablierung, ‐düngung sowie des Verlassens von Weiden auf Bodenkohlenstoff‐ und Nährstoffdynamik in einer tropischen Bergregenwaldregion Ecuadors zusammenfassend dargestellt und diskutiert. Der Naturwald des Untersuchungsgebietes ist seit Jahrzehnten durch Brandrodung und die Umwandlung in extensiv genutztes Weideland (aktive Weide) in seinem flächenhaften Bestand bedroht. Als Problem hat sich der Verlust an Fruchtbarkeit der Weideböden während ihrer Bewirtschaftung herausgestellt. Des Weiteren führt die Einwanderung des Tropischen Adlerfarns (Pteridium arachnoideum, C3‐Pflanze) zu einer Reduktion der oberirdischen Grasbiomasse. Nimmt diese Entwicklung überhand, werden die betroffenen Flächen von den Bauern nicht mehr aktiv genutzt, verlassen und neuer Regenwald gerodet. Um mehr über die Mechanismen der Verringerung der Bodenfruchtbarkeit zu erfahren, wurden biotische und abiotische Bodeneigenschaften und deren Interaktion entlang eines Landnutzungsgradienten (Naturwald – aktive Weide – verlassene Weide) untersucht. Die Zerstörung des Bergregenwaldökosystems und die Überführung der gerodeten Flächen zur Weidebewirtschaftung verändert die Funktion und Struktur der Bodenmikroorganismen und beeinflusst den CO2‐C Fluss aus dem Boden. Jährlich werden 2 t CO2‐C ha‐1 zusätzlich vom Weideland emittiert. Diese Erhöhung der Bodenatmungsraten kann mit erhöhten Raten der mikrobiellen C‐Mineralisierung und Feinwurzelatmung in Verbindung gebracht werden. Das Weidegras (S. sphacelata, C4‐Pflanze) liefert C‐ und N‐reiche ober und unterirdische organische Substanz (z.B. durch die Feinwurzelbiomasse) und trägt damit zu einer Erhöhung der C‐ und N‐Verfügbarkeit für die mikroorganismen bei. Darüber hinaus stellen ein höherer pH‐Wert und eine erhöhte Basensättigung im oberen Mineralboden der aktiven Weide günstige Bedingungen für mikrobielles Wachstum und Metabolismus dar. Als Konsequenz sind die Gehalte an mikrobiellem Biomassekohlenstoff um das Dreifache erhöht und die mikrobiellen Gemeinschaftsstrukturen signifikant in Richtung einer höheren relativen Abundanz der Gram(‐)‐Bakterien und Pilze verschoben. Eine längerfristige Weidebewirtschaftung ohne Kompensation von Nährstoffverlusten sowie die Einwanderung des Tropischen Adlerfarnes verschlechterte die Bedingungen für die Mikroorganismen, was zu einem signifikanten Rückgang des SOC, der Netto‐ und Brutto‐N‐Mineralisierungsraten sowie zu einer Halbierung der mikrobiellen Biomasse führt. Eine bevorzugte Substratnutzung von Graskohlenstoff (C4) durch die Mikroorganismen hat einen schnellen Abbau des C4‐Pools zur Folge. Somit dominiert nun der mikrobiell schlechter verfügbare C3‐Pool den Bodenkohlenstoffpool. Dies führt zu einem weiteren Rückgang der Weideproduktivität und schließlich zum Offenlassen der Weide. Die geringere Qualität und Quantität der vom Farn stammenden ober‐ und unterirdischen organischen Substanz (hoher Ligninanteil, weites C/N), führten zu einer Limitierung der Ressourcen für die Mikroorganismen, welche deren Funktionen in größerem Maße beeinflussen als deren Gemeinschaftsstruktur. Im Gegensatz dazu wird entlang des Landnutzungsgradienten die Struktur hauptsächlich durch den pH‐Wert beeinflusst. Daraus folgt, dass Struktur und Funktion der Bodenmikroorganismen voneinander entkoppelt auf Veränderungen reagieren können. Um den Einfluss von Harnstoff‐ und/ oder Rohphosphatdüngung aktiver Weiden auf die Dynamik der organischen Bodensubstanz und auf die Weideproduktivität zu untersuchen, wurden sowohl Labor‐ als auch Feldversuche durchgeführt. Im Feldexperiment wurde gezeigt, dass eine NP‐Limitierung der Grasbiomasseproduktion vorliegt und durch eine geringe NP‐Kombinationsdüngung die oberirdische Phytomasseproduktion um 2 t ha−1 a−1 gesteigert und die Futterqualität durch eine Erhöhung der P‐ und Ca‐ Gehalte verbessert werden kann. Die Mikroorganismen reagierten mit einer Anpassung ihrer Struktur an die kurzzeitig erhöhte Substratverfügbarkeit. Nach Gabe von Harnstoff und/ oder Rohphosphat wurde weder eine N‐ noch eine P‐Limitierung der Bodenmikroorganismen festgestellt, und die mikrobiellen Funktionen wurden langfristig nicht verändert. Dagegen bewirkte die Düngergabe einen erhöhten relativen Anteil der Pilzabundanz. Im Labor sowie im Feld kam es nach Harnstoffdüngung kurzzeitig zu verstärkten gasförmigen Verlusten des Bodenkohlenstoffs. Aufgrund der Landnutzungsänderungen im Untersuchungsgebiet veränderten sich die Ökosystemfunktionen stark, speziell die Boden‐C‐ und Boden‐N‐Umsatzraten. Für eine nachhaltige Landnutzung in der Region, d. h., für den Schutz der noch verbliebenen natürlichen Bergregenwaldflächen, ist es von entscheidender Bedeutung, dass die Weidedegradierung verhindert wird und degradierte Flächen wieder in Nutzung genommen werden. Als entscheidend für die Weideproduktivität hat sich in dieser Studie die Ressourcenverfügbarkeit für Bodenmikroorganismen herausgestellt. Daher ist es sehr wichtig, diese Ressourcenverfügbarkeit in Böden aktiv‐genutzter Weiden zu erhalten oder noch zu erhöhen, denn sie wirkt sich vor allem auf die organische Bodensubstanz und im Wechselspiel damit auf die mikrobielle Biomasse und Aktivität aus. Eine moderate Kombinationsdüngung aus Harnstoff und Rohphosphat ist ein erster Schritt in diese Richtung. Dabei sollte jedoch das Risiko zusätzlicher bodenbürtiger CO2‐C Emissionen in Folge höherer Düngergaben berücksichtigt werden. Für ein nachhaltiges Landnutzungsmanagement sind Maßnahmen gegen die Einwanderung des Adlerfarnes und ein angepasstes Nährstoffmanagement notwendig. Weitere Untersuchungen sollten auf eine Minimierung der Nährstoffverluste und eine erhöhte Nährstoffnutzungseffizienz der Pflanzen fokussiert werden. Weidemischkulturen aus Gräsern mit Leguminosen sowie der Einsatz von Kulturen mit speziellen Nährstoffaneignungsstrategien könnten dabei eine große Rolle spielen und sollten in der Region erprobt werden.:Contents Acknowledgement I Table of content III List of Tables V List of Figures VI Abbreviations VII Summary (English/German/Spanish) .................................................... 1 1 Introduction ................................................................................... 6 1.1 Impact of land‐use changes on C and nutrient dynamics ............... 6 1.1.1 Soil organic carbon and soil CO2 flux 7 1.1.2 The role of soil microbes 8 1.1.3 Plant‐microbe interactions 10 1.1.4 Impact of soil environment on soil microbes 11 1.2 Pasture establishment in the tropics .......................................... 13 1.3 Research area ....................................................................... .... 15 2 Objectives and research questions ......................... ................... 19 2.1 Land‐use change ........................................................................ 19 2.2 Pasture management ............................................................. ... 21 3 Methodology ................................................................................. 22 3.1 Study sites ............................................................................... 22 3.1.1 Land‐use gradient 22 3.1.2 Pasture Fertilization Experiment (FERPAST) 23 3.2 General analyses ....................................................................... 24 3.2.1 Laboratory experiments 25 3.2.2 In situ measurements 26 3.2.3 Statistics 27 4 Results ............................................................................................ 28 4.1 Soil C and nutrient dynamics along a land‐use gradient ............. 28 Potthast, K., Hamer, U., Makeschin, F., 2011. Land‐use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling. Biogeochemistry, 1‐17. 4.2 Impact of pH and ongoing succession on microbial function and structure .......... 29 4.3 Response of soil microbes to bracken‐invasion ........................... 32 Potthast K., Hamer U., Makeschin F. 2010. Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador. Soil Biology and Biochemistry 42, 56‐64. 4.4 Response of soil microbes and pasture grass to fertilization ........33 Hamer, U., Potthast, K., Makeschin, F., 2009. Urea fertilisation affected soil organic matter dynamics and microbial community structure in pasture soils of Southern Ecuador. Applied Soil Ecology 43, 226‐233. Potthast, K., Hamer, U., Makeschin, F., 2012. In an Ecuadorian pasture soil the growth of Setaria sphacelata, but not of soil microorganisms, is co‐limited by N and P. Applied Soil Ecology 62, 103‐114. 5 Discussion .................................................................................... 34 5.1 Impact of land‐use changes ...................................................... 34 5.1.1 Soil CO2 fluxes 34 5.1.2 Microbial structure and function 34 5.2 Soil fertility loss of pastures ‐reasons and first prevention steps‐ . 37 5.2.1 Litter decay and SOM dynamics 37 5.2.2 Fertilization and SOM dynamics 39 5.3 Conclusions and Perspectives ...................................................... 42 References ..................................................................................... 46 Curriculum vitae......................................................................... 58
La tesis presentada investiga el impacto del establecimiento de pasto, de su fertilización y de su manejo tradicional (abandono del pastizal) a la dinámica del carbono y de los nutrientes de suelo en la región de los bosques tropicales montañosos en el Sur de Ecuador. Durante las últimas décadas el bosque natural en el área de estudio ha estado amenazada por su conversión a pastizales. Sin embargo, la fertilidad del suelo en pastos de tipo extensivo (pastos activos) decrece frecuentemente durante el uso de los pastos. La invasión de Llashipa (Pteridium arachnoideum) conduce al abandono de los pastos cuando la ésta se vuelve dominante. Con la finalidad de revelar los mecanismos detrás de esta disminución de la fertilidad de suelo, se analizaron las propiedades bióticas y abióticas del suelo y sus interacciones, a lo largo de una gradiente del uso de la tierra (bosque natural —pasto activo — pastos abandonados). La perturbación del ecosistema de bosque tropical montañoso por su cambio de uso, mediante el establecimiento de pastizales, ha alterado la función y la estructura de los microorganismos y ha afectado el flujo de CO2‐C del suelo. Cada año 2 Mg CO2‐C ha‐1 fueron emitidas adicionalmente por el establecimiento de pastos. Esta aceleración en la tasa de respiración del suelo está relacionada con el aumento de las tasas de mineralización microbiana de carbono y de la respiración de las raíces. La alta calidad y abundancia de N de los residuos orgánicos del suelo con pasto Mequeron (S. sphacelata, C4‐planta), especialmente debido a la gran biomasa de las raíces finas, ofrecen una disponibilidad alta de C y N para los microorganismos. En comparación con el bosque natural, el aumento del pH y la saturación bases acelerada fueron condiciones más favorables para el crecimiento microbiano y para el metabolismo microbiano en el parte superior del suelo mineral en pastos activos. La cantidad de C de la biomasa de los microorganismos fue tres veces mayor que la del bosque y se ha observado un cambio significativo de la estructura de la comunidad microbiana, en donde la abundancia relativa de los hongos y de las bacterias Gram(‐) ha aumentado. El uso de pasto a largo plazo y la invasión de Llashipa (C3‐planta) han reducido los efectos benéficos para los microorganismos, que resultaron en una reducción significativa de las tasas de la mineralización de C y N, y en una reducción en dos tercios de la biomasa microbiana. El uso preferencial de los microorganismos por sustrato de pasto C4 han resultado en una rápida disminución de la reserva de C4. Como consecuencia, la menor disponibilidad de la reserva de C3 de las plantas de Llashipa y de la cobertura anterior de bosque ha incrementado su dominancia en la reserva de materia orgánica del suelo. Eso resulta, en una mayor disminución de la productividad de los pastos, conduciendo finalmente al abandono de los campos de pastos. La menor calidad y cantidad de los residuos acumulados sobre y bajo el suelo provenientes de la Llashipa han dado como resultado un sustrato de limitadas condiciones que están afectando más a las funciones microbiales antes que a su estructura. La estructura microbiana parece ser más sensible al pH del suelo a largo de la gradiente del uso de la tierra; de manera que se ha identificado una desconexión entre la estructura y función microbial. Experimentos de fertilización en laboratorio y en campo han sido realizados para evaluar el impacto de la aplicación de enmiendas (urea y/o roca fosfórica) a la dinámica de la materia orgánica y a la productividad de los pastos activos. El resultado del experimento de campo ha demostrado que la fertilización combinada es más efectiva, mostrando un aumento en la producción de biomasa de 2 Mg ha−1 a−1, lo que indica una limitación de N y P para el crecimiento del pasto. Además, la calidad de forraje se mostró incrementada ya que el contenido de P y de Ca han aumentado significativamente. Los microorganismos del suelo en el pasto activo han respondido a corto plazo con una adaptación de su estructura ante la disponibilidad de sustrato, pero no han mostrado un cambio de sus funciones iniciales a largo plazo. Después de la aplicación de urea y de la roca fosfórica, se detectó un incremento significativo en la abundancia de los hongos, pero tampoco se observó una limitación de energía microbial ni de N o P. Sin embargo, la aplicación de urea ha aumentado la pérdida gaseosa de CO2‐C del suelo a corto plazo. Debido al cambio de uso de la tierra en la área de investigación, se ha detectado una alteración notable de la función del ecosistema, especialmente en el ciclo de C y N de suelo. Para un uso sostenible de la tierra en esta región, es crucial el prevenir la degradación de pastos y rehabilitar aquellos degradados. En el suelo de pastos activos es de gran importancia el mantener o aún mejor el aumentar la disponibilidad del sustrato, que es uno de los indicadores de la fertilidad del suelo. En este contexto, la materia orgánica se debe ser retenida a largo plazo para mantener la actividad y biomasa microbiana alta y por ende la productividad de pasto. Una moderada fertilización con urea y roca fosfórica puede ser un primer paso para proveer un continuo suministro de nutrientes por el crecimiento del pasto y para reforzar la sanidad pecuaria por medio de un forraje de mayor calidad. Sin embargo, el riesgo de emisiones adicionales de CO2‐C del suelo debido a una aplicación más alta de urea debe tenerse en cuenta. Se puede concluir que para un manejo sostenible del uso de la tierra, tanto el control de la invasión de Llashipa y como un suministro adecuado de nutrientes son necesarios. Adicionalmente se podría decir que es necesario profundizar el estudio de la reducción de las pérdidas de los nutrientes de suelo y de la eficiencia del uso de los nutrientes en las plantas, así como las asociaciones de pastos con leguminosas o el uso de cultivos de absorción selectiva de nutrientes, que serían estrategias importantes para el futuro.:Contents Acknowledgement I Table of content III List of Tables V List of Figures VI Abbreviations VII Summary (English/German/Spanish) .................................................... 1 1 Introduction ................................................................................... 6 1.1 Impact of land‐use changes on C and nutrient dynamics ............... 6 1.1.1 Soil organic carbon and soil CO2 flux 7 1.1.2 The role of soil microbes 8 1.1.3 Plant‐microbe interactions 10 1.1.4 Impact of soil environment on soil microbes 11 1.2 Pasture establishment in the tropics .......................................... 13 1.3 Research area ....................................................................... .... 15 2 Objectives and research questions ......................... ................... 19 2.1 Land‐use change ........................................................................ 19 2.2 Pasture management ............................................................. ... 21 3 Methodology ................................................................................. 22 3.1 Study sites ............................................................................... 22 3.1.1 Land‐use gradient 22 3.1.2 Pasture Fertilization Experiment (FERPAST) 23 3.2 General analyses ....................................................................... 24 3.2.1 Laboratory experiments 25 3.2.2 In situ measurements 26 3.2.3 Statistics 27 4 Results ............................................................................................ 28 4.1 Soil C and nutrient dynamics along a land‐use gradient ............. 28 Potthast, K., Hamer, U., Makeschin, F., 2011. Land‐use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling. Biogeochemistry, 1‐17. 4.2 Impact of pH and ongoing succession on microbial function and structure .......... 29 4.3 Response of soil microbes to bracken‐invasion ........................... 32 Potthast K., Hamer U., Makeschin F. 2010. Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador. Soil Biology and Biochemistry 42, 56‐64. 4.4 Response of soil microbes and pasture grass to fertilization ........33 Hamer, U., Potthast, K., Makeschin, F., 2009. Urea fertilisation affected soil organic matter dynamics and microbial community structure in pasture soils of Southern Ecuador. Applied Soil Ecology 43, 226‐233. Potthast, K., Hamer, U., Makeschin, F., 2012. In an Ecuadorian pasture soil the growth of Setaria sphacelata, but not of soil microorganisms, is co‐limited by N and P. Applied Soil Ecology 62, 103‐114. 5 Discussion .................................................................................... 34 5.1 Impact of land‐use changes ...................................................... 34 5.1.1 Soil CO2 fluxes 34 5.1.2 Microbial structure and function 34 5.2 Soil fertility loss of pastures ‐reasons and first prevention steps‐ . 37 5.2.1 Litter decay and SOM dynamics 37 5.2.2 Fertilization and SOM dynamics 39 5.3 Conclusions and Perspectives ...................................................... 42 References ..................................................................................... 46 Curriculum vitae......................................................................... 58

The potential shortage of phosphorus (P) fertilizer is a threat to food security and closing the nutrient loop through recycling human excreta, especially urine, has been considered, so as to mitigate this crisis. Struvite (magnesium, ammonium phosphate), a material derived from human urine, is a product which is gaining credence with regards to using urine as a P amendment since more than 90% of P in urine can be captured during struvite production. A study to evaluate the potential of struvite as a P amendment in three contrasting soils was conducted. The soils used were an A horizon of Inanda (Ia), A horizon Sepane (Se) and an E horizon of Cartref (Cf). Phosphate adsorption properties of the soils were studied and the Freundlich model used to derive sorption parameters. From these studies, Pmax was related to the Kf parameter of the Freundlich equation. Two sets of incubation studies were then conducted. The first ran for 122 days and the second for 22 days to examine in closer detail the early stages of dissolution of the struvite as the major P release occurred during this time period of the incubation. A pot experiment was conducted in a controlled environment so as to determine the effect of P released from struvite on maize growth. The Ia, with high content of iron and aluminum oxides, displayed high sorption and affinity for P, whereas soil texture was a principal factor in the sorption properties of the Se (clayey) and Cf (sandy). The Kf decreased in the order Ia > Se > Cf and external P requirements decreased in the order Se > Ia > Cf. In the incubation studies solution P content increased with an increase in application rate of struvite. Struvite dissolution and P release varied between the different soils and the dissolution was found to be related to the P adsorption maximum of each individual soil and soil pH. The magnesium content also increased with time. In the glasshouse study, drymatter yield after six weeks growth was improved by the addition of struvite. There were no benefits achieved by using more than the recommended application rates for each soil. Struvite was as effective as conventional single superphosphate in the Ia and Cf, while superphosphate outperformed struvite on the Se. The findings of this study suggest that struvite has the potential to release P in an available form although its effectiveness and capability to release P could depend on soil pH, exchangeable acidity and initial P levels. Further research needs to focus on the effect of pH on struvite dissolution, the effect of struvite on soil pH, as well as comparison of nutrient release patterns between struvite and rock phosphate.
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Cereal rye (CR), the most common and effective nitrogen (N) scavenging cover crop option in the Midwest, is often utilized in cropping systems to reduce nitrate loss for environmental benefits. To increase environmental efficiency in Midwest corn cropping systems, we must increase the overall adoption of CR. However, due to the yield reduction potential (6%) for corn planted after CR termination, CR is primarily recommended before soybean. To increase CR adoption, we must develop adaptive fertilizer management practices that achieve competitive grain yields relative to cropping systems where CR is not adopted. Therefore, the objectives of this study are to determine (1) the effect of CR and starter nitrogen rate on corn growth and nitrogen content. (2) the optimum starter nitrogen rate to achieve agronomic optimum corn yield following CR. (3) the impact of phosphorus (P) at starter on plant growth, nitrogen content, and yield with the inclusion of CR. For our study, five starter N rates were applied in a 5x5 cm band to both CR and non-CR plots, concentrations ranged from 0-84 kg N ha^-1 in 28 kg N ha^-1 intervals. Total N applied was the same for each treatment, relative to its location, and was split between starter N at planting and sidedress applied at growth stage V6 relatively. Although CR termination took place at least two weeks before planting, CR decreased corn grain yield at one of three locations by an average of 8%, nitrogen recovery efficiency (NRE) by 27%, and R6 total N content by 23%, relative to the conventional control (non-CR 0N), when no starter N was applied. At one of three locations, starter N rates of 56 kg N ha^-1, 56 kg N ha^-1 plus 17 kg P ha^-1, and 84 kg N ha^-1 increased corn grain yield, in CR plots, and 56 kg N ha^-1 plus 17 kg P ha^-1 increased corn grain yield in non-CR plots. Phosphorus increased corn grain N content at growth stage R6 in one of three locations and did not impact corn grain yield at all locations. We conclude that the inclusion of starter N at planting has the potential to increase agronomic productivity in CR corn cropping systems in soil environments with a high capacity to mineralize soil N. However, further research is required to refine our starter N results to find an optimum starter N rate to apply before planting corn following CR.