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1
Carter, E. Thomas Jr. "Risk assessment formulation for nitrate leaching". Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/40347.
Testo completo
2
Carter, E. Thomas. "Risk assessment formulation for nitrate leaching /". This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-11182008-063039/.
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3
Wakida-Kusunoki, Fernando T. "Potential nitrate leaching from house building to groundwater". Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251274.
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4
Ottman, M. J., e J. E. Watson. "Nitrate Leaching Potential from a Single Border-Flood Irrigation". College of Agriculture, University of Arizona (Tucson, AZ), 1991. http://hdl.handle.net/10150/201383.
Testo completoAbstract (sommario):
Groundwater contamination by nitrate and other chemicals is a public concern and has subjected agriculture to scrutiny. Field studies were conducted at the Maricopa and Marana Agricultural Centers in 1989 to 1990 to document nitrate leaching potential with border flood irrigation. Calcium nitrate fertilizer was applied at various rates along with potassium bromide, which serves as an additional indicator of nitrate movement. Approximately 8.55 inches of irrigation water was applied at the Maricopa site on a sandy loam soil and 4.0 inches of irrigation water was applied at the Marana site on a clay loam soil. At the Maricopa site, only 64% of the nitrate could be accounted for in the top 6.7 ft. while most of the nitrate was found in the top 4 to 5 ft. at Marana. The water and nitrate moved 3 to 4 times deeper than predicted in the absence of preferential flow.
5
Cordell, Susan Chapman. "Nitrate losses beneath an irrigated cotton field". Thesis, The University of Arizona, 1994. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_e9791_1994_178_sip1_w.pdf&type=application/pdf.
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6
Matchett, Lisa Susanne. "Denitrification in riparian buffer zones". Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310427.
Testo completo
7
Ling, Ge. "Assessment of nitrate leaching in the unsaturated zone on Oahu". Thesis, Water Resources Research Center, 1996. http://hdl.handle.net/10125/21929.
Testo completoAbstract (sommario):
Groundwater contamination caused by agricultural fertilization is a widely recognized problem. In Hawaii, nitrogen fertilization from pineapple and sugarcane fields has posed a threat to several basal aquifers and has been implicated in coastal algae blooms. The concentration of nitrate-N in the Pearl Harbor basin on the island of Oahu was below 2.3 mg/L in the 1950’s and 1960’s, and has increased to as much as 7.6 mg/L in 1992 to 1994. The objective of this dissertation research is to develop a practical methodology for realistically estimating nitrate leaching from fertilized agricultural lands.
Numerous mechanisms have impact on the distribution and migration of nitrate in the soil. Nitrogen fertilizer undergoes many N transformations and interactions with the soil and the plant after applications. In this study, an analysis of soil samples was performed to understand the leaching process of nitrate in the root zone of three different cropped fields in Hawaii. A detailed discussion is given to address various factors which control the nitrate transport process. To judge the sampling plan in relation to spatial variation, the field measurements were evaluated statistically by an uncertainty index, which is represented as the density of samples required for the estimate of sample mean of the nitrate concentration to fall within a defined limit of accuracy.
In order to predict the effect of nitrogen fertilization on the groundwater contamination with very limited input data, a simple, analytical, lumped parameter model (LPM), was developed. The model can estimate the average nitrate leaching from the root zone in response to agricultural practices, N transformations and other related processes. The model was tested against the field data and two detailed numerical models, LEACHM-N and CERES-Maize. It provides an alternative way to assess nitrate leaching from the root zone with acceptable accuracy. A listing of the program is provided in Appendix 2.
Owing to the complex nature of nitrogen behavior in the unsaturated zone, some degree of uncertainty is involved in the development of modeling approaches. In this study, five major sources of uncertainty were identified. These are: uncertainty due to spatial variation, uncertainty related to the accuracy of the input data, uncertainty due to simplifications in the development of the models, uncertainty due to the modeling parameters, and uncertainty due to the complexity of the unsaturated zone in Hawaii. The impact of these uncertainties on simulation results is evaluated.Thesis (Ph. D.)--University of Hawaii at Manoa, 1996.
Includes bibliographical references (leaves 202-215).
UHM: Has both book and microform.
Water Resources Research Center, University of Hawaii at Manoa
8
Elder, Linda A. "Water table height and nitrate leaching in undisturbed soil columns". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/27874.
Testo completoAbstract (sommario):
Water table control by subsurface drainage has been shown to affect leaching losses of nitrate-nitrogen: a concern both for economic use of fertilizer, and for maintenance of water quality. The effect of water table height on leaching of NO₃⁻-N was investigated in this study in nineteen 15cm x 100cm undisturbed cores of silty clay loam. The experiment simulated fertilization followed by rainfall, then rapid water table rise and fall, under conditions similiar to those experienced in the early spring in the Lower Fraser Valley. In the first part of the experiment, a concentrated solution of KNO₃ and KG (equivalent to 35 kg/ha of N and 22 kg/ha of Cl) was applied to the columns, followed by intermittent leaching with distilled water. Leachate from two depths in each column was collected before and after a period of static water table, and analyzed for NO₃⁻, No₂⁻, NH₄⁺, and Cl⁻. This procedure was repeated without nutrient addition in the second part of the experiment. Chloride was used an inert tracer to follow anion movement and retention within the columns. There was no significant difference in the leachate NO₃⁻ concentration or leachate N/CI ratio from any of the four water table heights tested (15, 35, 55, and 75 cm above drain depth). The NO₃⁻ concentrations and N/CI ratios decreased with depth in the soil columns, indicating removal of N from the percolating soil solution, either by denitrification or immobilization. The variability in leachate concentrations among all columns was very high (eg. for a typical sample time, NO₃⁻-N ranged from 0.01 to 15.72 mg/L, and Cl⁻ ranged from 4.8 to 14.5 mg/L), as was the variability in constant head satiated hydraulic conductivities (range: 1 to 1468 cm/day; CV = 181%), and drainable porosity (range: 2.7 to 10.4%; CV = 39%). Cross sections of columns leached with 1% methylene blue solution did not reveal differences in patterns of water transmission between low and high conductivity columns. Indications were that penetration of dye was greater in columns with higher conductivities, and that preferential flow occurred in all columns examined. Leachate concentrations and N/CI ratios correlated significantly with hydraulic conductivity: Spearman's correlation coefficients were always > 0.8 for samples obtained from the bottom of the columns. However, even when the conductivity was included as a covariate in an analysis of covariance, there was no significant effect of water table height on nitrate leaching.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
9
Baigys, Giedrius. "Soil water regime and nitrate leaching dynamics applying no-tillage". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20090217_111111-32108.
Testo completoAbstract (sommario):
The impact of different agricultural systems used in agriculture on the leaching of nutrients and nitrates first of all depends on many factors that are not noticed and sometimes even underestimated by farmers trying to reach larger yields and better economic results. This article analysis the issue of changes in water regime and nitrate nitrogen leaching under the change of agricultural systems; such issue has not been investigated in Lithuania before. This research is especially relevant under the conditions of the Middle Lithuanian Lowland, where annual crops (cereals and sugar beet) area mainly cultivated, the ground is aerated in-tensely thus increasing the mineralization of organic substances and a lot of fertilizers are used. The change of conventional tillage for reduced tillage resulted in the decrease of the resources of surface soil water by 4,91-5,85 % and after changing it into no-tillage water resources decreased by 23,4 %. Reduced tillage and late ploughing are appropriate environmental means reducing nitrate nitrogen leaching from soil.Įvairių žemdirbystės sistemų naudojamų žemės ūkyje poveikis maisto medžiagų ir labiausiai nitratų išsiplovimui priklauso nuo daugelio veiksnių, kurių žemdirbiai siekdami didesnių derlių ir geresnių ekonominių rezultatų nepastebi, o kartais ir reikiamai neįvertina. Šiame darbe, nagrinėjamas šalyje netirtas vandens režimo ir nitratų azoto išplovimo pasikeitimų, keičiantis žemdirbystės sistemoms, klausimas. Šie tyrimai ypač aktualūs Lietuvos Vidurio lygumos sąlygomis, kur daugiausia auginama vienmečių augalų (javų ir cukrinių runkelių), kasmet žemė intensyviai aeruojama, taip didinant organinių medžiagų mineralizaciją, naudojama daug trąšų. Pakeitus tradicinį žemės dirbimą į sumažintą žemės dirbimą paviršinio dirvožemio sluoksnio vandens atsargos sumažėjo 4,91-5,85 %, o pakeitus į neariminį žemės dirbimą vandens atsargos sumažėjo 23,4 %. Sumažintas žemės dirbimas bei vėlyvas arimas yra tinkamos aplinkosauginės priemonės, mažinančios nitratų azoto išplovimą iš dirvožemio.
10
Shah, Sanjay Bikram. "Agronomic and Nitrate Leaching Impacts of Pelletized versus Granular Urea". Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/29201.
Testo completoAbstract (sommario):
Agronomic and water quality impacts of urea particle size were evaluated through field and laboratory experiments and mathematical modeling. In a two-year field study, corn silage yield, corn nitrogen (N) removal, and nitrate-N (NO₃⁻-N) leaching from urea pellets (1.5 g each) and granules (0.01-0.02 g each) applied at 184 kg-N/ha were compared. A control treatment (no N) and two other N application rates (110 and 258 kg-N/ha) were also included. Urea particle size impact on dissolution rate, dissolved urea movement, mineralization, and N0³-N leaching were evaluated in the laboratory. A two-dimensional (2-D) mathematical model was developed to simulate the fate of subsurface-banded urea and its transformation products, ammonium (NH₄⁺)and NO₃⁻.
With 184 kg-N/ha, corn silage yield was 15% higher (p = 0.02) and corn N removal was 19% higher (p = 0.07) with pellets than granules in the second year of the field study. In the absence of yield response at 110 kg-N/ha, reason for higher yield at 184 kg-N/ha with pellets was unclear. Greater N removal reduced NO₃⁻-N leaching potential from pellets compared to granules during the over-winter period. No urea form response to yield or corn N removal was observed in the first year. In 23 of 27 sampling events, granules had higher NO₃⁻-N concentration in the root zone than pellets, with average nitrate-N concentrations of 2.6 and 2.2 mg-N/L, respectively. However, statistically, NO₃⁻-N leaching from the root zone was unaffected by urea form, probably due to high variability within treatments masking the treatment effects. In October 1997, pellets retained 16% more (p = 0.04) inorganic-N in the top half of the root zone than granules, due to slower nitrification in pellets as was determined in the mineralization study. Slower NO₃⁻-N leaching allowed for greater N extraction by plants. Pellets had lower dissolution, urea hydrolysis, and nitrification rates than granules; however, nitrification inhibition was the dominant mechanism controlling N fate.
The model took into account high substrate concentration effects on N transformations, important for simulating the fate of band-applied N. The model exhibited good mass conservative properties, robustness, and expected moisture and N distribution profiles. Differences in measured field data and model outputs were likely due to uncertainties and errors in measured data and input parameters. Model calibration results indicated that moisture-related parameters greatly affected N fate simulation. Sensitivity analyses indicated the importance of nitrification-related parameters in N simulation, particularly, their possible multiplicative effects. Need for extensive model testing and validation was recognized. The validated 2-D N model could be incorporated into a management model for better management of subsurface-banded granular N. However, the 2-D model is not appropriate for simulating the three dimensional N movement from pellets.Ph. D.
11
Silgram, Martyn. "Hydrological controls on nitrate leaching : an integrated fieldwork and modelling study". Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267286.
Testo completo
12
Stoewer, Myriam Maria [Verfasser], e Christine [Akademischer Betreuer] Stumpp. "Vulnerability assessment of nitrate leaching on the regional scale using isotope techniques". Freiburg : Universität, 2016. http://d-nb.info/1119717485/34.
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13
Chabon, Joshua D. "Irrigation management effects on nitrate leaching and mowing requirements of tall fescue". Thesis, Kansas State University, 2014. http://hdl.handle.net/2097/17716.
Testo completoAbstract (sommario):
Master of ScienceDepartment of Horticulture, Forestry, and Recreation Resources
Dale J. Bremer
Jack D. Fry
Irrigation management may influence nitrate leaching under tall fescue (Festuca arundinacea) and also affect its mowing requirements. Two experiments were conducted on tall fescue growing on a Chase silt loam soil near Manhattan, Kansas. Each experiment was arranged in a split-plot design, with irrigation treatments applied to whole plots: 1) frequency-based irrigation, water was applied three times weekly to deliver a total of 19 mm water wk⁻¹ regardless of weather conditions; and 2) soil moisture sensor (SMS)--based irrigation, 34 mm of water was applied when soil dried to a predetermined threshold. In the first experiment, sub-plots consisted of unfertilized turf, and N applied as urea or polymer-coated urea at 122 and 244 kg ha⁻¹ yr⁻¹. Suction lysimeters at a 0.76 m depth were used to extract nitrate leachate bi-monthly. Turf quality was rated weekly. In the second experiment, subplots were mown at 5.1 cm or 8.9 cm, based upon the 1/3 rule, with or without monthly applications of the growth regulator trinexapac-ethyl (TE). Data were collected on total mowings and visual turf quality. Soil moisture sensor-based irrigation resulted in water savings of 32 to 70% compared to frequency-based irrigation. Leaching levels did not exceed 0.6 mg L⁻¹ and no differences in leaching were observed between irrigation treatments or among N sources. All fertilized turf had acceptable quality throughout the study. In the second experiment, irrigation strategy did not influence total number of mowings. In the first year, TE application reduced total mowings by 3 in tall fescue mowed at 5.1 cm, but only by 1.5 when mowed at 8.9 cm. In the second year, mowing at 8.9 vs. 5.1 cm or using TE vs. not resulted in a 9% reduction in total mowings each. The SMS-based irrigation saved significant amounts of water applied compared to frequency-based irrigation, while maintaining acceptable quality, but irrigation treatments did not affect nitrate leaching or mowing frequency in tall fescue on fine silt-loam soil. Nitrate leaching, regardless of amount, was well below the standards set for human health (10 mg L⁻¹). Applications of TE are more beneficial for turfgrass mowed at lower cutting heights.
14
Yazid, Sadek Mohammed. "Solute leaching studies in cropped field plots and laboratory columns using nitrate, bromide and chloride tracers". Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/27726.
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Thurtell, Stephen W. "Nitrate leaching from nursery sod production as affected by nitrogen and water management". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq24511.pdf.
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Roy, James W. "Infiltration, nitrate and chloride leaching, and dicamba fate in unsaturated soil below turfgrass". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ35929.pdf.
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17
Rydberg, Ingrid. "Breeding of catch crops : a way to reduce nitrate leaching from arable land /". Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1998. http://epsilon.slu.se/avh/1998/91-576-5525-1.gif.
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18
Conrad, Yvonne [Verfasser]. "Model-based quantification of nitrate-nitrogen leaching considering sources of uncertainty / Yvonne Conrad". Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1128149249/34.
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19
Qi, Zhiming. "Monitoring and modeling of subsurface drainage and nitrate leaching under various land covers". [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3389138.
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20
Branson, Johannah Helen. "The farm-level impact of policies to reduce nitrate emission from livestock waste : an economic analysis". Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300519.
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Dennis, S. J. "Nitrate leaching and nitrous oxide emission from grazed grassland: upscaling from lysimeters to farm". Lincoln University, 2009. http://hdl.handle.net/10182/1269.
Testo completoAbstract (sommario):
Irish agriculture is becoming increasingly regulated, with restrictions on fertiliser application rates and stocking rates to reduce nitrate (NO₀⁻) leaching losses. However these regulations have been, to date, based on minimal field research. The purpose of this study was to determine the actual leaching losses of nitrate from Irish dairy pasture at a range of stocking rates, and to investigate the effectiveness of the nitrification inhibitor DCD at reducing nitrate leaching losses where these are deemed excessive. In grazed pastures, a major source of leached nitrate is the urine patch, where a high rate of N is applied in one application. This trial recorded the losses from urine and non-urine areas of pasture separately. Nitrate leaching losses from three soils were recorded using lysimeters at Johnstown Castle, Co. Wexford, over two years. Total nitrate losses were higher from the freely drained Clonakilty and Elton soils than from the heavy Rathangan soil. Mean nitrate losses from urine patches ranged from 16 - 233 kg nitrate-N / ha⁻¹, and were reduced by up to 53% when DCD was applied. DCD also reduced peak and mean nitrate-N concentrations in many cases. In addition, DCD halved the nitrous oxide (N₂O) emission factor on the Rathangan soil, caused increases in pasture N content, and increased herbage yield in some treatments. The distribution of urine patches under dairy grazing was recorded using GPS at Kilworth, Co. Cork. Cows were also found to deposit 0.359 urine patches per grazing hour. A model was produced to predict field-scale nitrate leaching losses from dairy pasture at a range of stocking rates. At 2.94 cows per hectare, the highest stocking rate, annual field N loss was below 34 kg nitrate-N ha⁻¹, mean drainage N concentrations were below 5.65 mg nitrate-N L⁻¹ (the EU drinking water guideline value), and the worst-case-scenario autumn peak concentration did not exceed 21.55 mg nitrate-N L⁻¹ (above the EU Maximum Allowable Concentration (MAC) but below the World Health Organisation (WHO) drinking water limit). DCD reduced total annual field N loss by 21% (a conservative estimate), and also reduced mean and peak nitrate concentrations. Provided fertiliser application rates are at or below 291 kg N ha⁻¹, and based on current legislative values for drinking water quality, this trial does not support any blanket restrictions on the stocking rate of Irish dairy farms. However where particularly high water quality is required, DCD shows potential as a useful tool to achieve low nitrate concentrations.
22
Grift, Sheri L. "Impact of leaching and denitrification on temporal distribution of nitrate in several Manitoba soils". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ62741.pdf.
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23
Burgess, Magdalena S. E. "Nitrate leaching from a subsurface-drained corn field under different tillage and residue levels". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=55481.
Testo completoAbstract (sommario):
Nitrate leaching was studied on a 2.4-ha subsurface-drained corn (Zea mays L.) field in southwestern Quebec. The soil was a sandy loam to loamy sand (mean depth 46 cm) overlying clay. Treatments, begun in fall 1991, consisted of no-till, reduced tillage, and conventional tillage with crop residues either removed or retained at harvest. Drain flow volume and NO$ sb3 sp-$-N concentrations in flow were monitored year-round, and soil NO$ sb3 sp-$-N levels measured in spring and fall. A total of 34 kg NO$ sb3 sp-$-N ha$ sp{-1}$ was recorded in drain flow in 1992 from the site as a whole, equivalent to 20% of applied fertilizer N. In the first 14 months of monitoring, over 70% of water samples had NO$ sb3 sp-$-N levels exceeding Canadian drinking water guidelines (10 mg NO$ sb3 sp-$-N L$ sp{-1}),$ and about 25% had over 40 mg NO$ sb3 sp-$-N L$ sp{-1}.$ Flow-weighted mean concentration for the site as a whole in 1992 was 19 mg NO$ sb3 sp-$-N L$ sp{-1}.$ Unanticipated variations in drain depth significantly affected flow volume and total NO$ sb3 sp-$-N losses, hampering assessment of treatment effects on drain water parameters. In 1992, post-harvest soil NO$ sb3 sp-$-N levels at 0-25 cm were significantly lower in plots with crop residues retained, regardless of tillage system, than in plots with residues removed. In May 1993 (pre-tillage), soil NO$ sb3 sp-$-N levels were similar for all treatments, having dropped in no-residue plots and risen slightly in plots with residues, suggesting immobilization of NO$ sb3 sp-$-N by crop residues in summer-fall and mineralization in spring. The NO$ sb3 sp-$-N measured in drain flow represents a substantial loss of N from the farm system, and has negative implications for water quality. Within the time-frame of the study, crop residues appeared to have a greater effect on soil NO$ sb3 sp-$-N levels, and thus leaching potential, than did tillage system.
24
Johnson, Terrence G. "A model of nitrate leaching from agricultural systems in the northern neck of Virginia". Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/37887.
Testo completoAbstract (sommario):
A model (VTCROPS) was developed to simulate the long-term effects of nitrogen (N) leaching to groundwater in the Northern Neck region of Virginia, and ultimately to the Chesapeake Bay. VTCROPS simulates N fate and transport in a soil-plant-atmosphere continuum in a vertical slice between two crop rows, enabling consideration of nonuniform fertilizer placement and root growth patterns. VTCROPS models atmospheric, soil and crop subsystems. Atmospheric conditions (rainfall, temperature, solar radiation) may be directly input by the user or generated using a stochastic climatic generator. The soil subsystem simulates runoff, infiltration, drainage and soil-water redistribution, N immobilization, nitrification, mineralization, denitrification and advective N transport. The crop subsystem simulates plant N uptake, and vegetative and reproductive growth in response to soil and climatic factors, explicitly for maize or wheat. VTCROPS simulates soybean in a crop rotation empirically accounting for leaf area and root growth. The model is capable of simulating long-term cropping sequences under minimum and conventional tillage practices for continuous maize or for rotations involving maize, wheat, soybean and fallow.
Critical internal model parameters were calibrated through comparison of output to field data. The sensitivity of output to input variables was determined. Model output is most sensitive to the climatic variables. Model predicted crop performance variables — grain and total dry matter yields and N content — and soil N content were compared with available field data from two sites over a three year period for maize. Data from six sites over a one year period were tested for wheat. Predictions for maize and total N content were fairly accurate, with a tendency to greater error in dry years. Predictions for wheat were somewhat less accurate, but incomplete field data precluded determining the source of discrepancies.
Long-term model predictions, for two year crop rotations with minimum and conventional tillage, were evaluated by comparing performance variables with literature values. Appropriate responses were obtained for N transformation processes. Mass conservation for soil-water and N were good. Maize performance variables were within the range of literature values, and were higher under minimum till. Wheat yields and N contents were somewhat higher than values reported in the literature. Nitrogen load is correlated to drainage and water use over the short run, and to rainfall and drainage over longer periods. Minimum tillage did not increase N load to groundwater. Over a year nitrogen load was strongly periodic, with most leaching taking place from January through April. More than 50% of the N load over a rotation was lost during an extended fallow period that followed soybeans. Nitrogen load increased with fertilizer rates, however, N leaching fraction was optimal around rates of 150 — 200 kg/ha.
The model was applied to the Virginia counties of Richmond, Westmoreland, Lancaster, King George and Northumberland to assess the potential for long term N leaching to groundwater. Soil surveys indicated that 34 soil map units occurred within 123,000 hectares of cultivated land. In order to reduce the number of simulations, principal component analysis and cluster analysis were employed to subdivide the cultivated area into 10 land units based on different soil properties. Historical climatic data from the area was used to calibrate the stochastic climatic generator.
Analyses were performed to determine long-term crop performance and N loads to ground and surface waters in the study area over a 26 year period (13 rotations). Two management systems were applied to the land units. The first management system consisted of a rotation of minimum tilled maize, conventionally tilled wheat, minimum tilled soybeans and a fallow period. The second management system had a similar cropping sequence, but all crops were conventionally tilled. In both cases, fertilizer was applied at a rate of 150 kg-N/ha/crop. With the exception of two land units, mean yield, water use and N uptake over the simulation was fairly uniform among the land units. Runoff and drainage were highly variable between land units and over time within units. Mineralization, denitrification and N load were highly variable both between land units and over time. Nitrogen load ranged from 66 to 131 kg/ha/rotation between land units.
Long-term average N loads and N concentrations from the cultivated area and from the total area of the study region were estimated. For this analysis it was assumed that 80% of the cultivated area was under minimum till and 20% under conventional tillage. An area-weighted average of 5.4 million kg-N/ha/year or 29% of total N applied is discharged to groundwater with an average drainage concentration of 9.9 mg/L. The average N concentration from the study area (including uncultivated areas) to groundwater is estimated at 5.1 mg/L. Average N concentration to the Chesapeake Bay from all sources, after dilution with runoff is 4.5 mg/L which is lower than the drinking water standard for nitrate N of 10 mg/L.
The possibility of using sewage sludge as a replacement for, or in consort with N fertilizer was investigated for a typical land unit, under a conventionally tilled maize-wheat- soybean-fallow rotation. Simulations were conducted with 100%, 50% and 0% sludge (C—N ratio of 12). With fertilizer N augmenting the sludge, the total N input (250 kg/ha) was the same for each treatment. Mean yields were similar for 50% and zero sludge, but lowered by 10% and 16%, respectively, for maize and wheat with 100% sludge. Discrepancies in yields were attributed to the fact that mineralization rates of sludge are not high enough to supply the crop N requirement during periods of peak uptake. Nitrate leaching was reduced by 41 and 25% with 100 and 50% sludge applications, respectively.Ph. D.
25
Johnson, Terrence Guilford. "A model of nitrate leaching from agricultural systems in the northern neck of Virginia /". This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-05222007-091359/.
Testo completo
26
Saha, Subhrajit Kumar. "Effect of fertilizer source on nitrate leaching, plant water consumption, and turf and ornamental quality". [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0003300.
Testo completo
27
Rosenqvist, Lars. "Afforestation of former arable land in north-western Europe : nitrate leaching, carbon sequestration and water recharge /". Uppsala : Dept. of Forest Soils, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/200702.pdf.
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Almadni, Mftah Alhusen Alhadi. "Impact of agricultural management on risks of nitrate leaching in crop rotations with potatoes and cereals". Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2713.
Testo completoAbstract (sommario):
There is concern about increased nitrate levels in drinking water due to potential impacts on human health. At the same time there are also concerns about the environmental impact of increased levels of nitrate in surface water systems; the increased amount of nitrate in surface water can cause eutrophication. It has become almost axiomatic that nitrate which comes from agriculture soils is one of the main drivers of the increased nitrate levels in water. Arable agriculture is considered to be one of the main sources of nitrate due to high rates of nitrogen fertiliser or manure application, non-synchronous application of fertiliser with crop demand and inappropriate management of soil and water. Therefore minimise nitrate losses from agriculture soils could help to reduce nitrate level in ground and surface waters. This PhD study aims to improve the recommendations that are available to farmers to minimise nitrate leaching from arable rotations under UK conditions by investigating the impact of typical agricultural management practices on the risks of nitrate leaching in crop rotations with potatoes and cereals. In the conclusion, the achievements of this PhD study are evaluated with reference to the original aims and objectives. Then recommendations for further work to develop the understanding of nitrate leaching in arable rotations are made.
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Martin, E. C., E. J. Pegelow e J. Watson. "Assessing the Impact of Irrigation Management Strategies on Yield and Nitrate Leaching in Upland Cotton Production". College of Agriculture, University of Arizona (Tucson, AZ), 1996. http://hdl.handle.net/10150/210898.
Testo completoAbstract (sommario):
Although the cost for water is one of the largest expenditures in a grower's budget, many growers still over -irrigate their fields to assure that there will be no yield losses. Although these over -irrigations usually do not cause any negative effect to the crop, they can cause the loss of available nitrogen to the plant and the potential of nitrate contamination of groundwater resources. To assess what impact over-irrigation may have on yield and the potential for groundwater contamination, a drainage lysimeter study was initiated at the Maricopa Agricultural Center, Maricopa Arizona. Drainage lysimeters are large steel boxes with the tops open. In this study, three lysimeters were installed. The lysimeters were 80" wide (two row widths), five feet long, and six feet deep. They were placed 18 inches below the soil surface and filled with soil as to best represent the soil in its natural condition. On April 10, cotton was dry planted and watered up. Throughout the season, water samples were taken from the lysimeters and from suction lysimeters placed in the field. Nitrogen applications were made according to field conditions and weekly petiole sampling. Irrigations were made according to field conditions and using the AZSCHED irrigation scheduling program. Treatment one was irrigated according to the schedule and amount recommended by AZSCHED. In treatment two, the timing was the same as treatment one, but the amount applied was 0.25 times more. Treatment three was also irrigated at the same time but with 0.5 times more water. Yield samples were taken at the end of the season and showed no significant differences between treatments, with yields averaging about 1100 lbs /acre of lint. The drainage amounts ranged from 4" in treatment three to 1.5 inches in treatment one. The corresponding nitrate -N losses were 33 lbs/acre for treatment three and 20 lbs/acre for treatment one. Monitoring will continue over the winter to assess the impact of winter rainfall.
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roitero, manuele. "ACHIEVING THE NITRATE DIRECTIVE: FIELD MEASUREMENTS AND SIMULATION APPROACH". Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3422358.
Testo completoAbstract (sommario):
Sustainable crop production requires nitrogen (N) and phosphorus (P) inputs to compensate for the elements removed from the system by plant uptake and losses. Often, however, Losses of N are positively related to input levels. Also the effect of climate (precipitation) and soil properties can promote or limit N loss. Agricultural losses should be minimized as they largely determine the quality of water bodies. The relationship between animal density and water quality in Europe, has lead the European Union, throughout the Nitrates Directive, to set a limit of 170 kg N manure ha per year as a precautionary application threshold for regions that are vulnerable to N leaching. Also, although application rates can affect environmental quality of the water bodies, the effective environmental effects are determined by all inputs and outputs together instead of the manure input only. Farming in general is undeniably associated with the risk of exceeding the EU target of 11.3 ppm, especially because manures are inherently difficult to manage. The purposes of this thesis were to i) evaluate the performances of the N limits, imposed by the EU nitrate Directive, in limiting N loss in groundwater, ii) identify the best agricultural practices applicable in the Veneto Region in order to control the nitrate pollution, and iii) evaluate the performance of the EU Nitrate Directive limits under the effect of the climate change, from 2010 to 2100. Results show that nitrate in drainage water was influenced by N and water inputs. Higher concentrations were measured theses fertilized with the higher amount of N (400 kg N ha-1) while lower ones at lower N rates (145 kg N ha-1). Water inputs clearly affected NO3-N concentration in the drainage water. Higher concentrations were measured in plots irrigated with the lower amount of water (800 mm), while lower concentrations were found in plots with higher water inputs (1700 mm). The EU target of 11.3 ppm was exceeded for the 5% of the total measurements under 1700 mm, while 30% at 800 mm yr-1.
Simulations that the EU Nitrate Directive threshold of 170 kg N ha-1 did not exceed the 11.3 ppm at any water inputs considered in our scenarios. Also it has never exceeded the EU target 11.3 ppm at any water inputs considered in our scenarios. Maize on loamy soil in the north of Italy can utilize fertilizer N up to 340 kg ha-1 without exceeding a target value of 11.3 mg l-1 in the groundwater. However, the water input should not exceed 1100 mm annually. However, our results suggest fertilizations should be reduced to between 235 and 270 when water inputs are greater than 1100 mm. Simulations revealed that N-cycle and crop grain yield may be sensitive to gradually increasing temperature, days of drought and decreasing of precipitation. Nitrate-N concentration could increase about +11.3% at the end of the simulation, while crop maize production could decrease about -10.5% at the end of simulation. Despite simulations showed that N loss could increase in the future, the EU limit of 170N has never exceed the threshold of 11.3 ppm at any water inputs considered in our scenarios. In contrast, the EU limit of 340N exceeded always the concentration of 11.3 ppm NO3-N, however, 340N was less effective in limiting N loss at the end of the simulation. Results, also suggest when annual water inputs (irrigation) are lower than 400 mm a reduction of the N fertilizations from 340 to 230 kg N ha-1 should allow to limit N loss and, at the same time, reach high crop maize production, This thesis provide useful information about the behavior of the N loss at the N rate allowed to the EU Nitrate Directive. Our results provide interesting information that can be useful in order to improve the management of N fertilizations and maximize crop productivity, in view of complying with the European environmental policy both during an initial phase and a long term period. Nonetheless our results provide scientific basis and references for governments' decision-making from the view of regional climate change response.Una produzione sostenibile richiede inputs di azoto (N) e fosforo (P) per compensare sia le asportazioni che le perdite a livello campo. Spesso però, le perdite di azoto sono positivamente correlate alle quantità di azoto distribuito. A tutto ciò va poi sommato l’effetto del clima (piovosità) e della caratteristiche del suolo, nel promuovere o limitare le perdite di N. In linea generale, le perdite di nutrienti, in particolare di N, dovrebbero essere minimizzate in quanto, identificate come causa principale dell’inquinamento dei corpi idrici. La relazione tra l’incremento della densità animale nelle aziende zootecniche e la qualità delle acque su scala europea, ha spinto la Comunità Europea con la legge EU 91/676 a fissare un limite massimo di N di origine zootecnica pari a 170 kg N ha-1, come valore massimo precauzionale per aree individuate come “sensibili all’inquinamento da nitrati”. Sebbene i fertilizzanti di origine zootecnica possano contribuire all’inquinamento dei corpi acquiferi, va però, sottolineato che l'"effetto inquinante" delle fertilizzazioni azotate va determinato considerando inputs e outputs isieme, invece che del solo input. E’ comunque, innegabile che gli insediamenti zootecnici sia legato ad un maggior rischio di eccedere i limiti imposti dalla Direttiva Nitrati di 11.3 mg-l, specialmente perché le deiezioni zootecniche, generalmente, sono difficili da gestire. La tesi ha valuta i) la capacità dei limiti imposti dalla EU Direttiva Nitrati, nel limitare le perdite di azoto in falda ii) la determinazione delle migliori pratiche agricole applicabili a parte della Regione Veneto per controllare le perdite di N e iii) la valutazione dei limiti EU 91/676 nel contenere i rilasci, sotto l’effetto dei cambiamenti climatici durante il periodo 2010-2100. I risultati ottenuti mostrano che i nitrati nell’acqua di drenaggio sono influenzati sia dagli inputs di N e acqua (irrigazioni+pioggia). Alte concentrazioni di NO3-N sono state osservate nelle tesi concimate con le più alte quantità di fertilizzante (400 kg N ha-1), mentre le più basse a quantità minori (145 kg N ha-1). L’acqua distribuita ha influenzato la concentrazione di nitrato nell’acqua di drenaggio. Alte concentrazioni (>40 ppm) sono state misurate in tesi irrigate con 800 mm acqua, mentre molto basse nelle tesi irrigate con le quantità più alte di acqua (1700 mm). Il limite di 11.3 ppm è stato superato solo il 5% delle misurazioni ad 1700 mm mentre, per il 30% ad 800 mm. I risultati della modellizzazione ha messo in luce un ottima capacità del limite 170 kg N ha-1 nel prevenire il superamento di 11.3 ppm NO3-N, all’interno delle aree vulnerabili. Inoltre, la concentrazione di 11.3 ppm non è mai stata superata in nessuno dei numerosi scenari testati a differente quantità di acqua (irrigazione+pioggia). Il limite di 340 kg N ha-1, (aree non vulnerabili), ha mostrato buona capacità nel controllare le lisciviazioni solo ad l’input d’acqua inferiori a 1100 mm/anno. Oltre, 1200 mm, al fine di rispettare i limiti UE, si consiglia di ridurre le concimazioni a 230-250 kg N ha-1. I cambiamenti climatici potrebbero avere un forte impatto sia sullo sviluppo delle piante che sul ciclo dell’azoto, sotto la spinta di un incremento dei giorni di siccità e delle temperature. La concentrazione di NO3-N nell’acqua di drenaggio potrebbe aumentare del +11.3% al 2080, mentre la produzione di mais potrebbe diminuire del -10.5 % al 2080. Nonostante le simulazioni abbiano messo in luce un trend di incremento delle lisciviazioni nel prossimo futuro, il limite UE 170N, non ha mai ecceduto la concentrazione di 11.3 ppm a tutte gli inputs di acqua simulati. Il limite UE 340N ha ecceduto sempre il limite di 11.3, anche se il superamento del limite è più consistente alla fine del periodo della simulazione. I risultati, suggeriscono altresì, che una riduzione delle inputs azotati da 340 a 230 kg N ha-1, consentirebbe sia di limitare i rilasci di nitrati (soprattutto ad input superiori a 400 mm annui) che di ottenere produzioni, lievemente inferiori, ma economicamente remunerative. La tesi fornisce risultati interessanti sul comportamento dei rilasci dei nitrati misurati alle dosi massime di N organico ammissibili dalla Direttiva Nitrati. Questo studio ha altresì, fornito indicazioni molto importanti nell’uso nelle quantità massime di N utilizzabili per limitarne le lisciviazioni, nel breve periodo che nel lungo (sotto l’effetto dei cambiamenti climatici). Nondimeno questa tesi fornisce basi scientifiche per decisioni governative.
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Tedesco, Sara. "Avaliação das práticas de gestão da rega e da fertilização nas hortas urbanas de Lisboa: experimentação e modelação. Contributos para uma agricultura urbana ambientalmente sustentável". Master's thesis, ISA/UTL, 2013. http://hdl.handle.net/10400.5/5652.
Testo completoAbstract (sommario):
Mestrado em Engenharia Agronómica - Instituto Superior de AgronomiaThis work aims to study the water and nitrogen (N) related processes in several Urban Gardens of Lisbon and to find alternative management practices in order to minimize the N losses. The applied methodology integrates field experiments and modeling. Five allotments were selected as case studies and characterized in terms of soils and agricultural management practices. The water and N related processes were modeled with RZWQM2. After calibration, RZWQM2 accurately simulated the evolution of the N profiles after the summer and winter fertilization events. The water and N budgets highlight the Granja’s soils leaching potential, estimating an annual drainage of 261 mm and 300 mm for each allotment, containing 230.3 and 359.8 mg L-1 NO3 -. The Ajuda system does not show significant leaching, but the N accumulated below the root zone is high (324 and 518 Kg N-NO3 ha-1). The proposed alternative practices are: control the irrigation frequency by using tensiometers; prepare the organic compost aiming for a C/N within the desired range; fraction the chemical fertilizer applications, or even to discontinue it in the conventional plots due to the adequate soil fertility. Also, given the variability of urban farm management, the quantification of water/N budgets by modeling is suggested
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Carli, Roberto Simão de. "DINÂMICA DO NITROGÊNIO INFLUENCIADA PELA ADUBAÇÃO NITROGENADA E ADIÇÃO DE GESSO EM SISTEMA PLANTIO DIRETO DE LONGA DURAÇÃO". UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2016. http://tede2.uepg.br/jspui/handle/prefix/2295.
Testo completoAbstract (sommario):
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Previous issue date: 2016-06-29Nitrogen is a nutrient with such a high contribution for agriculture, that various strategies are studied every year looking for enhancements of its use efficiency and reduction of its environmental impacts. This study hypothesis is that, the use of gypsum can change the soil’s nitrogen dynamic in the no-tillage system. So, the main objective of this study was to relate the dynamic of the labile compartments of C and N as indicators of fewer losses or lower efficiency of Nitrogen by the use of gypsum under a well-established no-till system. The objective was to relate the dynamics of labile compartments C and N as loss of reduction or efficiency indicators of N due to the use of gypsum in no-tillage system. The experiment was established in September 2012 on clay Oxisol in Ponta Grossa – PR, in a split-split plot completely randomized block design, with three replications. The sources of variation were used gypsum (plots), nitrogen (split-plots) and time (split-split plots). The corn sowing was done in September 2014. The treatments used in the plots were gypsum rates: a) absence of gypsum and b) 2.7 Mg ha-1 of gypsum applied surface. Treatments of subplots were: a) 0 kg ha-1 N; b) 80 kg ha-1 N; c) 160 kg ha-1 N and d) 240 kg ha-1 applied on corn at the V4 stage phenological (four leaves expanded). The time factor was inserted as split-split plots: a) 0 days after sowing (DAS); b) 34 DAS; c) 52 DAS; d) 87 DAS and e) 117 DAS. Within the first and the fifth time layers were sampled 0-5 cm, 5-10 cm, 10-20 cm, 20-40 cm and 40-60 cm. For intermediate times were sampled layers up to 20 cm. The variables analyzed were: a) Nitrate; b) hot water extractable organic carbon (HWEOC); c) permanganate oxidizable organic carbon (POXC); d) Total Organic Carbon (TOC) and e) Total Nitrogen (TN). It was also held for sampling density in the layers referred to only in the first season. Straw samples were collected for reading C and Total N was also evaluated the decomposition of crop residues. The corn production was studied in function of the treatments employed. The use of gypsum become an important tool to minimize the environmental impact nitrate leaching. In high fertility areas and therefore no chemical deterrents in depth to achieve high production ceilings, low doses of plaster do not provide increases in corn yields, but changes in labile compartments C are observed. In long term experiments changes should be seen in TOC and NT and consequently grain production in responses can be observed.
O nitrogênio é um nutriente de grande contribuição para a atividade agrícola, desta forma várias estratégias são estudadas cujo intuito é a maximização da eficiência associada à minimização dos impactos ambientais. O presente trabalho parte da hipótese que o uso do gesso agrícola altera a dinâmica do nitrogênio no solo em sistema plantio direto. Dessa forma o objetivo geral foi relacionar a dinâmica dos compartimentos lábeis de C e N como indicadores da redução de perda ou eficiência do N devido ao uso do gesso agrícola em sistema plantio direto de longa duração. O experimento foi implantado em setembro de 2012 em um Latossolo Vermelho distrófico argiloso em Ponta Grossa – PR. O delineamento experimental foi em parcelas sub-subdivididas com três repetições. As fontes de variação empregadas foram gesso agrícola (parcelas), doses de nitrogênio (sub-parcelas) e o tempo (sub-subparcelas). A semeadura do milho ocorreu em setembro de 2014. Os tratamentos empregados nas parcelas foram doses de gesso: a) ausência de gesso e b) 2,7 Mg ha-1 de gesso, aplicados em superfície. Os tratamentos que compuseram as subparcelas foram: a) ausência de N; b) 80 kg ha-1 de N; c) 160 kg ha-1 de N e d) 240 kg ha-1 aplicados no milho no estágio fenológico de V4 (quatro folhas verdadeiras expandidas). O fator tempo foi inserido como sub-subparcela, sendo que as avaliações foram realizadas em a) 0 dias após semeadura (DAS); b) 34 DAS; c) 52 DAS; d) 87 DAS e e) 117 DAS. Dentro da primeira e da quinta época foram amostradas as camadas 0-5 cm, 5-10 cm, 10-20 cm, 20-40 cm e 40-60 cm. Para as épocas intermediárias foram amostradas as camadas até 20 cm. As variáveis analisadas foram: a) Nitrato; b) Carbono extraído em água quente (C-AQ); c) carbono oxidado por permanganato (C-OXP); d) Carbono Orgânico Total (COT) e e) Nitrogênio Total (NT). Também foi realizada amostragem para densidade nas camadas referidas apenas na primeira época. Amostras de palha foram coletadas para leitura de C e N total, também foi avaliada a decomposição dos resíduos culturais. A produtividade do milho foi estudada em função dos tratamentos empregados. O uso do gesso se torna uma ferramenta importante para minimizar o impacto ambiental pela lixiviação de nitrato. Em áreas de alta fertilidade e consequentemente sem impedimentos químicos em profundidade para alcançar altos tetos produtivos, doses baixas de gesso não proporcionam incrementos na produtividade do milho, porém alterações nos compartimentos lábeis do C são observadas. Em experimentos que contemplem maior tempo, mudanças devem ser observadas nos estoques de COT e NT e consequentemente respostas em produção de grãos poderão ser observadas.
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Serem, Vincent Kipyego Arap. "Effects of tillage and corn residues on nitrate-nitrogen and water movement through soil". Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29130.
Testo completoAbstract (sommario):
Laboratory soil columns, 0.3 m diameter $ times$ 0.7 m long, and two computer simulation models, LEACHM-N and NTRM, were used to investigate nitrate-nitrogen ($ rm NO sb{3 sp{-}}$-N) leaching in a sandy loam soil. The following treatments were studied: no-till (NT), reduced tillage (RT), and conventional tillage (CT) practices, with residue (R) and without residue (NR). Nitrogen fertilizer was applied at a rate of 180 kg/ha in granular form (experiment I), and in solution form a year later (experiment II). In both experiments, water was applied 5 times over 3 to 4 weeks duration, with each application lasting for 30 minutes. Each column received an average of 24 mm water in experiment I and 32 mm in experiment II. Soil moisture contents were measured and water for $ rm NO sb{3 sp{-}}$-N concentration determination sampled at 0.1, 0.2, 0.4, and 0.6 m depths, following each water application.In each experiment I, higher nitrate-nitrogen concentrations ($ lbrack rm NO sb{3 sp{-}}$-N)), occurred at the 0.1 and 0.2 m soil layers in RT and CT treatments initially, but less leached to lower layers, while more $ rm NO sb{3 sp{-}}$-N leached to lower depths (below 0.4 m) in the NT treatment. In experiment II, more $ rm NO sb{3 sp{-}}$-N leached below 0.4 m in RT and CT than in NT treatments. Conventional tillage exhibited the lowest drainage rates. Tillage and residue effects were significant only at early stages (4 hours or before) at some depths of experiment I ($P<0.05$). Maximum $ lbrack rm NO sb{3 sp{-}}$-N) occurred at 0.4 m depth in all treatments.
LEACHM-N estimated more $ rm NO sb{3 sp{-}}$-N leaching below 0.4 m in RT and CT treatments than in NT treatment. The model performed poorly only immediately after fertilizer application, showing up to 50% deviation from observed data. Although LEACHM-N overpredicted $ lbrack rm NO sb{3 sp{-}}$-N) in the 0.2 m soil layers in all treatments, estimations remained within standard deviations of observed data. NTRM performed well below 0.4 m depths, but often underpredicted $ rm NO sb{3 sp{-}}$-N leaching at shallower depths.
From both the laboratory experiments and mathematical simulations it was concluded that when fertilizer is applied in granular form, no till practice is undesirable because deeper $ rm NO sb{3 sp{-}}$-N leaching (below 0.4 m) occurs. Reduced tillage may be the preferred choice in such a situation. When fertilizer is applied in solution, reduced and conventional tillage practices are undesirable because deeper $ rm NO sb{3 sp{-}}$-N leaching occurred. No till practice may be a better choice in such a case.
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Readman, Russell J. "The physiological basis and consequences for nitrate leaching of novel fertiliser strategies involving foliar fertilisation of wheat". Thesis, Open University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321312.
Testo completo
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Bae, Jinyong. "Role of nitrogen and clipping-return on turf growth and nitrate leaching in zoysiagrass (Zoysia japonica Steud.)". [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024923.
Testo completo
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Isse, Abdullahi. "Capacity of cover crops to capture excess fertilizer and maintain soil efficiency". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0021/MQ37132.pdf.
Testo completo
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Fabio, Eric. "INFLUENCE OF MOISTURE REGIME AND TREE SPECIES ON NITROGEN CYCLING AND DECOMPOSITION DYNAMICS IN DECIDUOUS FORESTS OF MAMMOTH CAVE NATIONAL PARK, KENTUCKY, USA". UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_theses/287.
Testo completoAbstract (sommario):
The study of biogeochemical cycles and their role in ecosystem function has helped to highlight the impacts of human activities on natural processes. However, our understanding of the effects of nitrogen (N) deposition on forested ecosystems remains limited due to the variable controls on N cycling. Soils, microclimate, and vegetation can influence rates and processes of N cycling, singly or in concert at multiple scales. Understanding how these factors influence N cycling across the landscape will help to elucidate the impacts of N deposition. The objectives of this study were to characterize variation in soils, microclimate and vegetation characteristics, and N cycling and decomposition dynamics across the landscape in a region impacted by N deposition. Relationships among these factors were explored to determine the main factors influencing N cycling and decomposition. Strong differences in net N mineralization and nitrification were found between forest stands with contrasting species composition and moisture availability. Nitrate production and leaching were related to sugar maple abundance, and base cation leaching was correlated with nitrate concentrations in soil solutions. Decomposition experiments were installed to examine the effects of substrate quality, microclimate and N availability on decay rates. Nitrogen amendments for the most part did not affect decomposition rates of wood and cellulose, and mass loss rates were correlated with microclimate and forest floor characteristics. In contrast, microclimate did not seem to affect leaf litter decay rates, and the results suggest that the presence of invertebrates may influence mass loss to a greater degree than moisture or litter quality. This work highlights the large degree of variability in N processing across the landscape and suggests that differences in microclimate and species composition may help to predict the impacts of chronic N deposition on N cycling and retention.
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Hughes, Robert Guy. "Delay in the leaching of nitrate caused by adsorption on two variable charge soils from the humid tropics". Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329334.
Testo completo
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Beckman, Marie. "Kvävestatus och risk för nitrifikation i två avverkade skogsområden i Halland". Thesis, Uppsala University, Department of Earth Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9282.
Testo completoAbstract (sommario):
Nitrogen deposition leads to environmental damage in areas where the nitrogen deposition is high. Southwest Sweden receives an annual nitrogen deposition of up to 20 kg N/ha. Nitrogen that is not assimilated by the vegetation is accumulated in the soil, which may lead to nitrogen saturation and an elevated risk of nitrogen leaching. Nitrogen leaching from forest areas in southern Sweden has proven to be higher than from agricultural areas, which have been thought to be the main contributors to elevated nitrogen levels in rivers and lakes. The amount of nitrogen that leaches depends on the fraction of the total nitrogen in the soil that consists of nitrate, since nitrate is easily transported through the soil. Nitrogen leaching increases after clear-cutting since the uptake by vegetation is greatly reduced.
In this study the soil chemistry of two clear-cut spruce stands in Halland, in southwest Sweden, has been analyzed. A previous study in these areas has indicated higher nitrate concentrations in the groundwater in one of the areas and thus a greater nitrogen leaching. Nitrogen deposition in the two areas is estimated to be the same and therefore the soil chemistry has been analyzed to evaluate if differences in the soil can have resulted in differences in the nitrate concentration in the groundwater. The hypothesis is that the area with higher nitrate concentrations in the groundwater has properties more favorable for nitrification, which would be especially apparent in a lower carbon to nitrogen ratio. The pH and storage of nitrate, ammonium, total carbon, total nitrogen and exchangeable cations was analyzed in soil samples from both areas. In addition, a study of stand properties and previous use of the areas was made.
The analyses performed in this study indicate that the soil properties could not explain the differences in nitrate concentration in the groundwater. The differences found between the areas were that the area with lower nitrate concentrations in the groundwater had higher nitrate and ammonium concentrations and higher pH in the soil. The reason for this might be that the soil in this area has larger capacity to bind elements. The fact that the soil samples were sampled during different seasons probably had a major effect on these results. The history and stand properties of the two areas were similar. According to site index one area was more fertile, which benefits nitrification. This fact was not confirmed by the analyses, but it probably caused the nitrification rate to be higher in this area.
Det stora nedfallet av föroreningar i form av kväve i framförallt sydvästra Sverige leder till försurning och övergödning av både skogsmarker och vattendrag. Kvävedepositionen i södra Sverige kan uppgå till 20 kg N/ha och år. Det kväve som inte tas upp av vegetationen ackumuleras i marken som efterhand riskerar att bli kvävemättad vilket ökar risken för kväveutlakning. Kväveutlakningen från svenska skogsmarker har visat sig kunna vara i samma storleksordning som från jordbruksmarker som anses vara en av de största orsakerna till ökande kvävehalter i sjöar och vattendrag. Kväveutlakningens storlek beror till stor del på hur stor del av markens kväveförråd som finns i den oorganiska formen nitrat eftersom den är en lättrörlig jon. Efter skogsavverkning ökar nitratutlakningen betydligt på grund av att det finns väldigt lite vegetation kvar som tar upp kväveföreningarna.
I den här studien har markkemin i två avverkade granskogsområden i Halland undersökts. Tidigare studier i dessa två områden har visat att halterna av nitrat var högre i grundvattnet i det ena området än i det andra, och således var även nitratutlakningen större i detta område. Eftersom kvävedepositionen anses vara densamma i de två områdena har markemin undersökts för att finna skillnader där som kan förklara de olika nitratnivåerna i grundvattnet. Hypotesen var att det ena området skulle ha mer gynnsamma förhållanden för nitrifikation, framförallt en lägre C/N-kvot. Markens förråd av nitrat- och ammoniumkväve, totalkol, totalkväve, utbytbara katjoner samt pH undersöktes i båda områdena. En studie av områdenas historia gjordes även för att kunna utesluta skillnader där som kunde ge upphov till skillnaden i nitrat i grundvattnet.
Slutsatsen som kan dras från studien är att de analyserade egenskaperna inte visade på mer gynnsamma förhållanden för nitrifikation i det ena området än i det andra. Ingen skillnad i C/N-kvot uppmättes. Skillnaderna som hittades var att området med lägst halter av nitrat i grundvattnet hade högst halter av oorganiskt kväve i marken och högre pH. Att nitrathalterna var högre i grundvattnet men inte i marken kan ha sin förklaring i att marken i det ena området har större förmåga att binda till sig kväve vilket gör att det inte lika lätt kommer ut i grundvattnet. Antagligen spelade det stor roll för dessa resultat att jordproven tagits vid olika årstider. Undersökningen av tidigare användningsområde i skogarna visade att de hade en tämligen liknade historia. Det ena området har enligt ståndortsindex högre bördighet vilket gynnar nitrifikation. Detta framgick dock inte av analyserna men är antagligen orsaken till de högre nitrathalterna i grundvattnet i detta område.
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Fuentes, San Román Ignacio Francisco. "Soil hydraulics associated with soil physical properties and their effects on nitrate leaching in the mediterranean zone of Chile". Tesis, Universidad de Chile, 2013. http://repositorio.uchile.cl/handle/2250/151712.
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Rodda, Harvey John Edward. "The development and application of a nitrogen cycle model to predict nitrate leaching from grassland catchments within the United Kingdom". Thesis, University of Exeter, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332282.
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Kunrath, Taise Robinson. "Sistemas integrados de produção agropecuária : o papel da pastagem na solução do dilema produção versus conservação". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/108535.
Testo completoAbstract (sommario):
Além dos fins produtivos, as pastagens desempenham importante papel na preservação ambiental e na dinâmica da atmosfera e hidrosfera. Esta tese apresenta dois trabalhos, que demonstram as duas faces da pastagem nos sistemas produtivos. O primeiro trabalho, se refere a produção aliada à conservação e teve por objetivos (i) verificar se existe padrão no comportamento das variáveis de produção animal de pastos manejados em diferentes alturas e (ii) identificar metas de manejo que aliem produção e conservação. Este trabalho foi desenvolvido em um sistema integrado de produção agropecuária (SIPA) de longo prazo (2001-2011), localizado na região sul do Brasil. Os tratamentos consistiram de quatro alturas de manejo do pasto: 10, 20, 30 e 40 cm, delineados em blocos ao acaso, com três repetições. Foram utilizados novilhos com idade inicial média de 12 meses, sob pastoreio contínuo com taxa de lotação variável. As variáveis de produção animal e de pasto estudadas mostraram-se afetadas pelos anos experimentais. No entanto, existe padrão nas relações entre produção animal e de pasto ao longo dos 10 anos de experimento. A altura de manejo do pasto de 30 cm permite o acúmulo de resíduo sobre o solo, que beneficia o SIPA, e que proporciona ganho animal satisfatório e estável ao longo dos anos. O segundo trabalho, de cunho conservacionista, objetivou avaliar (i) o efeito de diferentes períodos de duração da pastagem em sistemas de rotação de cultura na drenagem e lixiviação de nitrogênio; (ii) o impacto do nível de intensificação, mais precisamente do uso da adubação nitrogenada durante a fase de pastagens; e (iii) analisar se ocorre um pico de lixiviação após a saída da pastagem e retorno das culturas de grãos, como conseqüência de uma maior mineralização N. Foi realizado na Região centro-oeste da França, com uma base de dados de 9 anos, comparando sistemas de rotação de cultura de milho, trigo e cevada com diferentes períodos de participação de pastagem mista de Festuca arundinacea, Lolium perenne e Dactylis glomerata (0, 3, 6 e 20 anos). Concluiu-se que a introdução de pastagem na rotação de culturas reduz a concentração de nitrato na água drenada. Quanto maior o tempo de participação da pastagem, maior é a redução na concentração de nitrato e, consequentemente, menor a lixiviação de nitrogênio, independentemente da adubação nitrogenada durante a fase pastagem.Further to productive targets, grasslands present an important role in environmental preservation and the atmospheric and hydrospheric dynamics. This thesis presents both issues, demonstrating the two roles of pastures in productive systems. The first work, refers to production with to conservation, and the objective was (i) verifying the pattern in animal and pasture production under different swards heights and (ii) identifying management targets that combine production and conservation. This work was carried out in a long term integrated crop-livestock system (ICLS) (2001-2011) in Southern Brazil. Treatments consisted of four swards heights: 10, 20, 30 and 40 cm, in a randomized block design with three replicates. Steers 12 months old were used, under continuous grazing with variable stocking rates. Animal and sward production were affected by the years effect, however, there are pattern on animal-sward relationship throughout ten years of experiment. 30 cm sward height allows soil residue accumulation that enables satisfactory livestock weight gain along the years on ICLS. The second work, which had more conservation nature, had the objectives: (i) the quantification of the grassland effect on drainage water quality at the level of a whole crop rotation according to the duration of the “grassland” phase and then on the relative importance of grassland area vs arable cropping area in the land use system; (ii) the impact of the level of intensification and more precisely of the N fertilization use during the grassland phase; and (iii) the analysis of the risk for peak of nitrate leaching after grassland re-cultivation as a consequence of a higher N mineralization. This experiment was carried out in France middle-west with a 9 year data base, comparing maize, wheat and barley crop rotation systems with different mixture pastures (Festuca arundinacea, Lolium perenne and Dactylis glomerata) cycle participation (0, 3, 6 and 20 years). We concluded that the introduction of mowed grassland sequences with this arable crop rotation leads to a strong reduction of the nitrate concentration of the ground water, the more proportion of grassland within the rotation the more NO3- concentration is reduced, whatever the level of N fertilization during the grassland sequence.
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Miller, Gilbert D. "A Simulation of the Economic Effects of Alternative Soil Types and Nitrogen Sources on Nitrate Leaching on Irrigates Agriculture in Utah". DigitalCommons@USU, 1991. https://digitalcommons.usu.edu/etd/4041.
Testo completoAbstract (sommario):
The economic impact of reducing the amount of nitrate leached out of the root zone under irrigation in the arid West was examined. A general introduction into the nature of the problem and a review of the literature was provided in chapter I. In chapter ll the economic incentives of irrigation management were evaluated under the assumptions of both profit-maximizing and utility-maximizing (in reducing cost and effort expended in irrigation) decision-making criteria. The results indicate that there is a coincidence of interests of the farmer and the environment. Both behaviors result in less nitrate leaching than less profitable or less utilityproducing irrigating practices. In chapter lli the economic impact of reducing the amount of nitrate leached out of the root zone under irrigation with various nitrogen sources and application methods was examined. The economic incentives of nitrogen management were evaluated under the assumption of profit-maximizing behavior. The results indicate that there is a coincidence of interests for irrigators who respond to economic incentives and environmentalists who wish to reduce nitrate residuals in irrigation drainage and the groundwater. Profit-maximizing behavior results in less nitrate leaching than less profitable irrigating practices when salt balance is not a major concern.
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Andreucci, Mariana Pares. "Perdas nitrogenadas e recuperação aparente de nitrogênio em fontes de adubação de capim elefante". Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/11/11139/tde-20022008-165101/.
Testo completoAbstract (sommario):
O manejo eficiente de fertilizações nitrogenadas em sistemas de exploração a pasto é peça chave para que melhores índices produtivos sejam alcançados. O conhecimento das perdas intrínsecas a esta prática e de fontes nitrogenadas alterntivas às normalmente usadas proporciona a determinação de melhores eficiências e flexibilidade na escolha da forma do nitrogênio aplicado. Assim o presente estudo teve o objetivo de avaliar as perdas por lixiviação de nitrato e volatilização de amônia, juntamente com a recuperação aparente do nitrogênio, em pastagens de capim elefante manejadas sob elevada fertilidade do solo. O experimento foi conduzido em área do depzrtamento de Zootecnia da ESALQ/USP, em Piracicaba. Adotou-se o delineamento experimental blocos ao acaso, com quatro blocos e seis tratamentos, que constaram da aplicação de 100 kg de N.ha-1 por ciclo, sob a forma de uréia, nitrato de amônio, etserco de curral, cama de frango e ajifer. Ao todo foram realizados três ciclos de amostragem, de novembro de 2006 a fevereiro de 2007, totalizando a aplicação de 300 kg de N.ha-1. Todos os resultados foram submetidos ao teste t à 5% de significância para a realização da análise estatística. As médias de produção de foram maiores para os tratamentos adubados com cama de frango e esterco, sendo de 3878,89 kg MSV.ha-1 e 3873,67 kg MSV.ha-1, respectivamente. Não foram observadas diferenças entre as recuperações aparentes do nitrogênio aplicado. As perdas por lixiviação de nitrato foram diferentes somente entre os ciclos, como consequência dos maiores índices de precipitação observados no terceiro ciclo amostrado, que apresentou média de -0,2.10-4 kg de NO3-.ha-1dia-1. Os valores de amônia volatilizada foram diferentes entre os ciclos e entre os tratamentos, sendo que no primeiro ciclo as maiores perdas foram atribuídas ao esterco, com 20,58% do nitrogênio aplicado. A cama de frango apresentou as maiores perdas de volatilização durante o segundo ciclo, com perda de 10,71% do nitrogênio aplicado, enquanto no terceiro ciclo a uréia apresentou a maior perda de nitrogênio, com 22,23% do nitrogênio volatilizado. As perdas por volatilização mais expressivas foram registradas até 60 horas após a aplicação das fontes.The efficiency of nitrogen fertilization is one of the key elements to grass production. The knowledge of nitrogen losses within this practice associated with the application of alternative nitrogen sources provide efficient use and flexibility in choosing between nitrogen fertilizers. The objective of this study was to evaluate nitrate leaching, ammonium volatilization losses and apparent recovery of the applied nitrogen in elephant-grass pasture managed under high soil fertility. It was conducted at the Animal Science Department of ESALQ/USP, in Piraicaba - S.P. The statistical design was in complete randomized blocks, with four replicates and six treatments, which were the use of 100 kg N.ha-1 as urea, ammonium nitrate, dairy manure, chicken litter and ajifer. There were three cycles of evaluations, from November 2006 to February 2007, resulting in 300 kg N.ha-1 applied during the whole period. The results were statistically analysed by the t test with 5% significance. Chicken litter and dairy manure treatments provided the higher dry matter yields of 3878,89 DM.ha-1 and 3873,67 kg DM.ha-1, for each source respectively. Nitrate leaching losses were significant in the third cycle when -0,2.10-4 kg NO3-.ha-1.day-1 was lost. Ammonia volatilization was different between cycles and sources. In the first cycle the dairy manure resulted in higher losses of 26,42 kg N.ha-1. Chicken litter and urea lost 23,97 and 22,27 kg N.ha-1, respectively. In the second cycle urea presented the higher losses of 22,50, while dairy manure and chicken litter lost 6,01 and 15,88 kg N.ha-1. During the third cycle urea presented higher losses than , with 40,12 kg N.ha-1, dairy manure and chicken , which were 2,71 and 11,93 kg N.ha-1. Higher volatilization losses were observed until 60 hours after fertilization.
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Larsson, Martin. "Quantifying macropore flow effects on nitrate and pesticide leaching in a structured clay soil : field experiments and modelling with the MACRO and SOILN models /". Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5489-1.pdf.
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Zardo, Filho Renato. "GESSO AGRÍCOLA E ADUBAÇÃO NITROGENADA NA CULTURA DO MILHO EM SISTEMA PLANTIO DIRETO". UNIVERSIDADE ESTADUAL DE PONTA GROSSA, 2011. http://tede2.uepg.br/jspui/handle/prefix/2228.
Testo completoAbstract (sommario):
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A considerably part of the high nitrogen (N) rates applied in corn is not absorbed due root growth restriction by subsoil acidity. Gypsum is able to improve conditions for root growth and lead to greater N uptake efficiency, increasing corn yield. Thus to evaluate the effect of gypsum and N on top dressing on soil chemical attributes, root growth , mineral nutrition and corn development under no-tillage system, two experiments were carried out on a dystrophic clayey Typic Hapludox at Middle-South of Paraná State, being one field and another in undisturbed soil columns. In the field experiment, four rates of gypsum (0, 5, 10 and 15 t ha-1) and three rates of N-NH4NO3 (60, 120 and 180 kg ha-1) were set up into 4 × 3 factorial design with three replications. On soil columns, two gypsum rates (0 and 10 t ha-1) and two rates of N-NH4NO3 (0 and 180 kg ha-1) were used in a 2 × 2 factorial design with five replicates. In both experiments, gypsum was applied on the surface, one week before sowing and 45 kg N ha-1 was applied at sowing. Were analyzed the changes in chemical soil properties, root development, nutrient uptake by corn in both experiments. On the field experiment were quantified the yield and efficiency in N use, and on the columns experiment the amount of N-NO3 - leaching was determined 45 days after the application of gypsum when the plants were cut off. On field experiment, gypsum increased levels of Ca2+, S-SO4 2- and P also decreased the exchangeable Al3+ level on subsoil layers. N rates raised up N-NO3 - levels throughout the soil profile and Ca2+ in 0,4-0,6 m. The increase in Ca2+ and S-SO4 2 levels on soil profile, as well the decrease on Al3+ saturation by gypsum application, improved plant root growth, and increased N, P, K, Ca, S, Zn and Mn extraction by maize, leading in increased corn grain yield. On top of that, gypsum rates improved N use efficiency by corn. In the soil columns experiment, gypsum and N application improved the plants roots to higher depths, which results in better plants dry matter and greater N, P, K, Ca, Mg, and S extraction. The amount of N-NO3 - leached on soil columns was higher when N was applied without gypsum. Gypsum application increased N uptake by plants due the root system increase and also increased of S-SO4 2-supply in soil, thus reducing the amount of N-NO3 - in the soil and leached. This results showed that gypsum use reduce losses of N-NO3 - leached by increasing N plants uptake, having as a result better N use efficiency contributing to higher corn yield sustainability.
Grande parte do nitrogênio (N) aplicado na cultura do milho não é absorvido devido à restrição no desenvolvimento do sistema radicular decorrente da acidez no subsolo. O gesso agrícola, por ter capacidade de melhorar o ambiente para o crescimento das raízes, pode aumentar a eficiência da absorção de N pelas plantas e a produtividade de grãos de milho. Com o objetivo de avaliar os efeitos da aplicação de gesso e de N em cobertura nos atributos químicos do solo, no crescimento de raízes, na nutrição mineral e na performance do milho cultivado em sistema plantio direto, foram realizados dois experimentos, sendo um no campo e outro em colunas indeformadas de solo, em um Latossolo Vermelho distrófico textura argilosa da região Centro-Sul do Paraná. No experimento de campo, quatro doses de gesso (0, 5, 10 e 15 t ha-1) e três de N-NH4NO3 em cobertura (60, 120 e 180 kg ha-1) foram combinadas em esquema fatorial 4 × 3, com três repetições. No experimento em colunas de solo, foram utilizadas duas doses de gesso (0 e 10 t ha-1) e duas doses de N-NH4NO3 (0 e 180 kg ha-1), em esquema fatorial 2 × 2, com cinco repetições. Nos dois experimentos, o gesso foi aplicado em superfície, uma semana antes da semeadura, e foram empregados 45 kg ha-1 de N na semeadura. Nos dois experimentos foram avaliadas as alterações nos atributos químicos do solo, no crescimento radicular e na absorção de nutrientes pelas plantas. A produtividade de grãos e a eficiência no uso do N foram avaliadas no experimento de campo, e a quantidade de N-NO3 - lixiviada aos 45 dias após a aplicação de gesso, no momento do corte das plantas, foi avaliada no experimento em colunas de solo. No campo, a aplicação de gesso elevou os teores de Ca2+, S-SO4 2- e P no solo, e reduziu a saturação por Al3+ nas camadas do subsolo. As doses de N em cobertura aumentaram o teor de N-NO3 - ao longo do perfil do solo e o teor de Ca2+ na camada de 0,4-0,6 m. O aumento na disponibilidade de Ca2+ e de S-SO4 2- no perfil do solo, bem como a redução na saturação por Al3+ no subsolo, com a adição de gesso, favoreceram o crescimento radicular do milho, a extração de N, P, K, Ca, S, Zn e Mn pelas plantas e a produtividade de grãos. Além disso, as doses de gesso melhoraram a eficiência no uso do N pelo milho. No estudo em colunas de solo, a aplicação de gesso e de N melhoraram o crescimento das raízes em profundidade. O maior crescimento radicular resultou em maior produção de matéria seca da parte aérea e maior extração de N, P, K, Ca, Mg e S pelas plantas. A quantidade de N-NO3 - lixiviada nas colunas de solo foi maior com a aplicação de N na ausência de gesso. A aplicação de gesso aumentou a absorção de N pelas plantas,proveniente da adubação nitrogenada, em decorrência de aumento no crescimento radicular e no teor de S-SO4 2- disponível no solo, reduzindo, com isso, a quantidade de N-NO3 - lixiviada. Os resultados mostraram que o uso de gesso minimiza as perdas de N-NO3 - por lixiviação por aumentar a absorção de N pelas plantas, ocasionando melhoria na eficiência da adubação nitrogenada e contribuindo para o aumento da sustentabilidade da produção de milho.
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Kim, Youngsun [Verfasser], e John [Akademischer Betreuer] Tenhunen. "Estimation and mitigation assessment of N2O emission and nitrate leaching in a mountainous catchment in South Korea using the LandscapeDNDC model / Youngsun Kim. Betreuer: John Tenhunen". Bayreuth : Universität Bayreuth, 2015. http://d-nb.info/1068860499/34.
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Jebli, Mouad. "Caractérisation à l'échelle locale des propriétés mécaniques de l'interphase pâte de ciment-granulat : application à la lixiviation". Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT339/document.
Testo completoAbstract (sommario):
Ce travail de thèse est consacré à la caractérisation des propriétés mécaniques de l’interphase pâte de ciment-granulat au cours de l’hydratation et au cours de la dégradation chimique par lixiviation. La microstructure de l'interphase entre la pâte de ciment et les granulats est caractérisée par une porosité supérieure à celle de la pâte de ciment. Cette zone constitue un point de fragilité dans le béton et ses propriétés affectent fortement le comportement mécanique du béton à l’échelle macroscopique et à l’échelle de la structure. Dans ce travail, la résistance de l’interphase pâte de ciment-granulat est analysée expérimentalement à l'échelle locale. Des essais expérimentaux sont réalisés sur des composites constitués de granulats liés par une pâte de ciment portland préparée avec un rapport Eau/Ciment de 0,5. Des dispositifs expérimentaux dédiés ont été conçus et réalisés de manière à être adaptés à la taille et à la forme des échantillons. La forme des échantillons utilisés et les outils expérimentaux développés permettent de solliciter directement l’interphase. A différents stades de l'hydratation, des échantillons de pâte de ciment seule et des composites sont soumis à des essais de compression, de traction et de cisaillement direct. L’étude des propriétés mécaniques de l’interphase pâte de ciment-granulat révèle une faiblesse de cette zone en termes de propriétés mécaniques..Le protocole expérimental mis au point a permis d’étudier les effets du mécanisme de lixiviation du calcium au niveau de l’interphase sur les propriétés mécaniques du béton à l’échelle locale. Compte tenu du temps caractéristique long du phénomène de lixiviation, la mise en situation expérimentale au laboratoire est accélérée en remplaçant l’eau par une solution de nitrate d'ammonium. Afin de quantifier le développement et la cinétique de dégradation au niveau de la liaison cimentée, les fronts de lixiviation du béton sont caractérisés à différents degrés de dégradation en utilisant la phénolphtaléine comme traceur. Des essais mécaniques locaux (compression, traction et cisaillement) sont réalisés sur les composites et sur la pâte de ciment à différents temps de dégradation. L’étude de l’effet de la lixiviation à l’échelle locale montre le rôle important de l’interphase pâte de ciment-granulat lors du processus de dégradation chimique sur les propriétés mécaniques du compositeIn this work, we presents an experimental study to characterize the mechanical properties at the local scale of the cement paste-aggregate interface during hydration and during chemical degradation by leaching.It is generally accepted that the microstructure of the interface between the aggregates and the cement paste is characterized by a higher porosity than that of cement paste. This makes this zone a weak point in the concrete. The particular properties of this zone strongly influence the mechanical behavior of concrete. In this work, the mechanical properties of the cement paste-aggregate composite, are experimentally studied. The experimental tests are performed on composites at classical aggregate scale (one centimeter of section). These composite are composed by and Portland cement paste and aggregate. The cement paste is prepared with a water/cement ratio of 0.5. The shape of the prepared composites makes them convenient for direct tensile and shear tests. At different stages of hydration, we performed direct tensile and shear tests on the composites by means of specific devices. The same tests were carried out on the cement paste in order to compare with composites results. The shape of the prepared composites makes them convenient to characterize the cement paste-aggregate interface. At different stages of hydration, the composites are subjected to compression tests, direct tensile tests or shear tests. The study of the mechanical properties of the cement-aggregates interface revealed that the cement paste-aggregate interface is the weakest zone in the composite.An experimental protocol was developed to study the effects of calcium leaching mechanism at the cement paste-aggregate interface on the mechanical properties of the concrete. As the process of leaching with the deionised water occurs very slowly, the experimental study in the laboratory is accelerated by replacing the water by ammonium nitrate solution. To quantify the development and kinetics of degradation at the cemented bond, the concrete leaching fronts are characterized at different levels of degradation by using phenolphthalein. Local mechanical tests (compression, tensile and shear) are performed on composite and cement paste at different stages of degradation. The experimental results show that there is a leaching effect on the alteration of the mechanical properties at the cement paste-aggregate interface
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Paulo, Ezio Nalin de. "Avaliação do inibidor de nitrificação fosfato de 3,4-dimetilpirazol (DMPP) em três solos com gradiente textural, absorção e uso de nitrogênio em plantas de algodão". Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/64/64133/tde-17012013-140846/.
Testo completoAbstract (sommario):
A utilização de inibidores de nitrificação pode ser uma alternativa interessante para aumentar a eficiência do uso do fertilizante nitrogenado em diversas culturas, porém, essa alternativa vem sendo pouco estudada em condições de solo e clima do Brasil. Assim, objetivou-se com esse trabalho avaliar a eficiência do inibidor de nitrificação fosfato de 3,4-dimetilpirazol (DMPP) em três solos com gradiente textural, bem como avaliar o destino do nitrogênio (N-NO3-, N-NH4+ e 15N) no solo, a absorção e o uso do nitrogênio (N-total e 15N) nas plantas de algodão. Três experimentos foram montados e desenvolvidos. No primeiro foi efetuada a incubação do solo em condições de laboratório para avaliar a inibição da nitrificação pelo DMPP aplicado na forma de ureia e sulfonitrato de amônio (SNA) em três solos (Neossolo Quartzarênico - NQ, Latossolo Vermelho Amarelo - LVA, Latossolo Vermelho - LV). No segundo experimento plantas de algodão foram cultivadas em colunas de lixiviação com os mesmos solos, recebendo ureia e sulfonitrato de amônio, com e sem DMPP como fonte de N. Foram avaliados a produção de matéria seca, o acúmulo de nutrientes nas plantas, a eficiência de uso do N pelo algodoeiro, a lixiviação e a quantidade de N mineral no solo após o cultivo do algodão por 60 dias. No terceiro experimento, plantas de algodão foram cultivadas também em colunas lixiviação, porém, com um solo de textura média (Latossolo Vermelho Amarelo), o qual recebeu três doses de N em cobertura (50, 100 e 150 kg ha-1 de N) na forma de ureia marcada no isótopo 15N, com e sem DMPP. Foram avaliados a produção de matéria seca, teor de N e recuperação do N aplicado na planta, lixiviação de N, teor de N-total, nítrico e amoniacal no solo, e recuperação do N aplicado no solo após o cultivo do algodão, por 90 dias. Melhores resultados foram obtidos com a aplicação do DMPP em ureia em relação ao SNA. No experimento de incubação, o DMPP foi capaz de manter menor o teor de nitrato nos três solos analisados. A nitrificação do N na ureia foi mais rápida comparado ao SNA, o que permitiu melhor desempenho do inibidor na ureia em dois dos três solos estudados. O efeito do DMPP aumentou seguindo a seguinte ordem: NQ>LVA>LV. O inibidor foi mais eficiente nos solos com menor teor de argila e matéria orgânica. O uso do DMPP em ureia aplicada no solo arenoso (NQ) reduziu significativamente a lixiviação de N e aumentou a produção de matéria seca, a eficiência do uso do N e a absorção de fósforo pela planta. No solo de textura média (LVA), sob irrigação intensa, o DMPP reduziu significativamente as perdas de N do sistema e aumentou a recuperação do 15N aplicado na planta e no solo, o que, porém, não se traduziu em maior produção de matéria seca provavelmente pelo N não ter sido limitante, devido à mineralização da matéria orgânica. As atividades das enzimas redutase do nitrato e urease não diferiram entre tratamentos com e sem DMPPThe use of nitrification inhibitors may be an interesting alternative to increase nitrogen fertilizer use efficiency in different crops, although it has been little studied in soil and climate conditions of Brazil. This study aimed to evaluate the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in three soils with textural gradient (represented by clay percentage), as well as to evaluate the fate of soil nitrogen (N-NO3-, N-NH4+ and 15N), nitrogen uptake, and N-use efficiency (total-N and 15N) by cotton plants. Three experiments were set and carried out in a controlled environment. In the first one, a laboratory incubation was performed to evaluate the inhibition of nitrification by DMPP applied to urea and ammonium sulfate nitrate (ASN) in three soils (Typic Quartzipsammnet - NQ, Typic Hapludox - LVA, Rhodic Hapludox - LV). In the second experiment, leaching columns with the same soils were planted with cotton receiving ammonium sulfate nitrate and urea with or without DMPP as nitrogen source. It were evaluated plant dry matter yield (shoot plus roots), nutrient uptake and nitrogen use efficiency by cotton plants, as well as the nitrogen leaching, and mineral nitrogen amount in the soil after cotton growth, for 60 days. In the third experiment, leaching columns with a medium textured soil (LVA) were planted with cotton and received three nitrogen rates in topdressing (50, 100 and 150 kg ha-1) as 15N-urea with and without DMPP. The production of dry matter, nitrogen content and recovery of applied N in the plant and soil, as well as the nitrogen leaching, total nitrogen, nitrate and ammonium in the soil were evaluated after cotton growth for 90 days. Best results were obtained with the application of DMPP to urea than in ASN. In the incubation experiment, the DMPP was able to maintain lower nitrate content in the three soils. The nitrification of nitrogen from urea was faster than the one from ASN, which allowed a better performance of the inhibitor in the urea in two out of three soils analyzed. The effect of DMPP increased in the following order: NQ> LVA> LV. The inhibitor was more effective in soils with lower clay and organic matter contents. The use of DMPP in urea applied on the sandy soil (NQ) significantly reduced N leaching and increased dry matter production, nitrogen use efficiency and phosphorus uptake by cotton plants. In a medium textured soil (LVA) under intense irrigation, DMPP significantly reduced N losses in the system and increased the recovery of applied 15N in plant and soil, which however did not translate into higher dry matter production because nitrogen was probably not limiting. The activity of the enzymes nitrate reductase and urease were not different between treatments with and without DMPP
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Hasnat, Abul, University of Western Sydney, of Science Technology and Environment College e School of Environment and Agriculture. "Soil-water use and irrigation scheduling under fruit tree-turf alley cropping system in Hawkesbury Area". THESIS_CSTE_EAG_Hasnat_A.xml, 2003. http://handle.uws.edu.au:8081/1959.7/614.
Testo completoAbstract (sommario):
Efficient use of irrigation and nutrients are becoming increasingly important in commercial orchards in the Hawkesbury area. Proper irrigation scheduling practices can help in the better use of irrigation water and reduce environmental impacts. Field experiments were conducted during February 1999 to June 2000 to understand soil-water use, and to evaluate farmer’s irrigation practice under an alley cropping system consisting of turf and stone fruits. The study was carried out at Atlas Farm, 3.5 km from the University of Western Sydney, Hawkesbury campus. The experimental site is a floodplain of the Hawkesbury River. The river flows within 1 km of the farm boundaries. The study was conducted under the farmer’s existing irrigation water and nutrient management practices. The main aims of the thesis were to study the movement and redistribution of soil-water and soil-moisture dynamics in the turf and stone fruit alley cropping system and to understand deep percolation losses and nitrogen leaching using the water balance approach. The study indicated that drainage occurred mainly after heavy rainfall and when there was rainfall for a few consecutive days. Thus irrigation application should be delayed if there is a likelihood of rain in a few consecutive days to prevent loss of water due to deep drainage. Furthermore, the study showed irrigation scheduling was essential to reduce nitrate leaching in the field; that irrigation depths should be varied according to the stage of crop growth, and the proper timing of irrigation application could help reduce deep percolation and runoff losses.Master of Science (Hons) (Agriculture)