Auswahl der wissenschaftlichen Literatur zum Thema „Soils South Australia Phosphorus content“

This study was performed to better understand the chemical behaviour of P in a variety of alkaline soils from southern Australia. To do so, surface soil samples of 47 alkaline cropping soils from Upper Eyre Peninsula in South Australia and from western Victoria were collected. The 22 soils collected from Eyre Peninsula were Calcarosols, and those from western Victoria were Vertosols, Alkaline Duplex soils, Sodosols, and Red Brown Calcareous soils. Parameters included total and amorphous Al and Fe, organic C, organic P, CaCO3 content, P sorption characteristics, phosphorus buffer capacity, calcium lactate (Ca-Lac) extractable P, bicarbonate-extractable (Colwell) P, water-extractable P, anion exchange membrane extractable P (AEM-P), and isotopically exchangeable P (labile P). Concentrations of micronutrients in the Calcarosols were relatively low, considered to be a function of low clay contents. Given very low background Cd concentrations in the soils, it was estimated from Cd measurements that the majority of total P in the soils was derived from previous fertiliser applications. Phosphorus buffer capacities (PBCs) were relatively high in the Calcarosols and moderately high in the other alkaline soils. P sorption behaviour in the Calcarosols was a direct function of CaCO3 content, although in the other alkaline soils, amorphous Al and Fe oxides were the principal determinants of the P sorption behaviour. Both Colwell and Ca-Lac extractants dissolved non-labile P in the highly calcareous soils, whereas AEM appeared to only remove surface-adsorbed P. In addition, Colwell P values were positively related to PBC and to the slope term in the Freundlich model (Kf) when Kf > 10. It is suggested that AEM-P may be a better predictor of P availability in highly calcareous soils compared with the other extractants.

Recent field trials on alkaline soils in southern Australia showed significant grain yield responses to liquid compared with traditional granular forms of P fertiliser. However the advantages of liquid over granular P forms of fertiliser has not been consistent on all soil types. In order to better predict the soil types on which liquid P fertilisers are likely to have potential, a glasshouse trial was conducted to compare the responsiveness of wheat to both liquid and granular forms of P on a wide range of Australian soils. A granular P fertiliser (triple superphosphate) and 2 liquid fertilisers (phosphoric acid and ammonium polyphosphate) were compared at a rate equivalent to 12 kg P/ha in 29 soils representing many of the soil types used for grain production in Victoria and South Australia. Wheat biomass was enhanced by P application in 86% of the soils tested. In 62% of the P-responsive soils, wheat dry matter was significantly greater when liquid P fertilisers were used compared with the granular form. Chemical analysis of the soils tested showed that the better performance of liquid P forms was not correlated to total P concentration in soil, P buffer capacity, or P availability as measured by Colwell-P. However, there was a significant positive relationship between calcium carbonate (CaCO3) content of soil and wheat responsiveness to liquid P fertiliser.

The P sorption characteristics of 97 soils that are representative of the agricultural areas of Western Australia were described using Langmuir and Freundlich equations. The Langmuir P maximum (xm) ranged from 11 to 2132 �g g-1 soil and the Freundlich k coefficient ranged from 1 to 1681. Clay content, DCB Fe and Al, oxalate Fe and AL, and pyrophosphate Al were positively related to xm and k. By using stepwise regression analysis, the combination of DCB and oxalate-soluble A1 predicted more than 75% Of the variation in the P sorption coefficients. Reactive Al compounds may thus be responsible for much of the P sorption by these soils. Soil pH in 1 M NaF (pH 8.2), which is normally used for the detection of allophanic material, was strongly related to the P sorption coefficients and might therefore be used as a quick test for predicting the P sorption capacity of soils.

Data from more than 580 field experiments conducted in South Australia over the past 30 years have been re-examined to estimate extractable soil phosphorus (P) levels related to 90% maximum yield (C90) for 7 crop species (wheat, barley, oilseed rape, sunflower, field peas, faba beans, potato) and 3 types of legume-based pasture (subterranean clover, strawberry clover, annual medics). Data from both single-year and longer term experiments were evaluated. The C90 value for each species was derived from the relationship between proportional yield responsiveness to applied P fertiliser rates (determined as grain yield in crops and herbage yield in ungrazed pastures) and extractable P concentrations in surface soils sampled before sowing. Most data assessments involved the Colwell soil P test and soils sampled in autumn to 10 cm depth. When all data for a species were considered together, the relationship between proportional yield response to applied P and soil P status was typically variable, particularly where Colwell soil P concentration was around C90. When data could be grouped according to common soil types, soil surface texture, or P sorption indices (selected sites), better relationships were discerned. From such segregated data sets, different C90 estimates were derived for either different soil types or soil properties. We recommend that site descriptors associated with the supply of soil P to plant roots be determined as a matter of course in future P fertiliser experiments in South Australia. Given the above, we also contend that the Colwell soil P test is reasonably robust for estimating P fertiliser requirements for the diverse range of soils in the agricultural regions of the State. In medium- and longer term experiments, changes in Colwell soil P concentration were measured in the absence or presence of newly applied P fertiliser. The rate of change (mg soil P/kg per kg applied P/ha) appeared to vary with soil type (or soil properties) and, perhaps, cropping frequency. Relatively minor changes in soil P status were observed due to different tillage practices. In developing P fertiliser budgets, we conclude that a major knowledge gap exists for estimating the residual effectiveness of P fertiliser applied to diverse soil types under a wide range of South Australian farming systems.

Soil testing for plant-available phosphorus (P) in Australia is most commonly conducted using alkaline sodium bicarbonate extraction (Olsen or Colwell tests), followed by a colourimetric assay to measure the concentration of P in solution. Analysis by inductively coupled plasma (ICP) spectroscopy has become increasingly popular internationally for other soil P tests, especially Mehlich 3, due to its efficiency and ability to measure multiple elements in the one extract. The use of ICP in place of colourimetry has been used in some Australian laboratories for bicarbonate-extractable P. However, the method is known to measure forms of P (organic) that are not measured by the colourimetric assay. This study presents data comparing soil Colwell P measured by the 2 methods for 714 soil samples from pastoral sites in south-east New South Wales. Measurement by ICP consistently yielded significantly higher P concentrations than the colourimetric method (ICP-P = 1.122Col-P + 57.0, r2 = 0.95, P < 0.001). Differences between the 2 techniques were more marked in 0–20 mm than 0–100 mm depth soil samples, and in soils with greater clay contents, suggesting that the difference was related to soil organic matter, and thereby organic P contents. Relative differences were greatest in soils with lower P concentrations, i.e. within the agronomic optimum range of most interest to farmers. ICP analysis cannot be directly correlated with colourimetrically measured P in bicarbonate extracts, and would need to be developed and calibrated as a separate, new soil P test.

Liquid forms of phosphorus (P) have been shown to be more effective than granular P for promoting cereal growth in alkaline soils with high levels of free calcium carbonate on Eyre Peninsula, South Australia. However, the advantage of liquid over granular P forms of fertiliser has not been fully investigated across the wide range of soils used for grain production in Australia. A glasshouse pot experiment tested if liquid P fertilisers were more effective for growing spring wheat (Triticum aestivum L.) than granular P (monoammonium phosphate) in 28 soils from all over Australia with soil pH (H2O) ranging from 5.2 to 8.9. Application of liquid P resulted in greater shoot biomass, as measured after 4 weeks’ growth (mid to late tillering, Feeks growth stage 2–3), than granular P in 3 of the acidic to neutral soils and in 3 alkaline soils. Shoot dry matter responses of spring wheat to applied liquid or granular P were related to soil properties to determine if any of the properties predicted superior yield responses to liquid P. The calcium carbonate content of soil was the only soil property that significantly contributed to predicting when liquid P was more effective than granular P. Five soil P test procedures (Bray, Colwell, resin, isotopically exchangeable P, and diffusive gradients in thin films (DGT)) were assessed to determine their ability to measure soil test P on subsamples of soil collected before the experiment started. These soil test values were then related to the dry matter shoot yields to assess their ability to predict wheat yield responses to P applied as liquid or granular P. All 5 soil test procedures provided a reasonable prediction of dry matter responses to applied P as either liquid or granular P, with the resin P test having a slightly greater predictive capacity on the range of soils tested. The findings of this investigation suggest that liquid P fertilisers do have some potential applications in non-calcareous soils and confirm current recommendations for use of liquid P fertiliser to grow cereal crops in highly calcareous soils. Soil P testing procedures require local calibration for response to the P source that is going to be used to amend P deficiency.

The response of oilseed rape to applied nitrogen and phosphorus was investigated in 2 areas of the South East of South Australia. The nitrogen rates applied varied from 0 to 50 kg/ha, while phosphorus rates applied in the Mundulla area ranged from 0 to 20 kg/ha and 0 to 34 kg/ha in the Millicent area. At 9 sites in the Mundulla area, where soils were primarily sandy loam over clay, oilseed rape yields were increased significantly by applied nitrogen at 7 sites and by applied phosphorus at 2 sites. On heavy black clay and peat soils in the Millicent area, oilseed rape yields were increased significantly by applied nitrogen at 5 of the 12 sites and by applied phosphorus at 6 sites. Of the measured soil variables, anaerobic ammonium nitrogen measured in the top 10 cm best predicted responses in seed yield to applied nitrogen. The critical nutrient range was 45-65 mg/kg. The response of oilseed rape to applied nitrogen was highly correlated with past paddock use but varied between the 2 areas. From the prediction equations developed, it was concluded that, in the Mundulla area, a significant (P< 0.05) nitrogen response was likely if the oilseed rape followed 2 or more crops, the last a non-legume, but was unlikely if the oilseed rape followed 1 or more years of pasture. At Millicent, a nitrogen response was likely if the oilseed rape was grown as the sixth crop in a continuous cropping program, and was unlikely if it was the first or second crop in the rotation, provided the preceding crop was a non-legume. The response of oilseed rape to applied phosphorus was highly correlated to extractable soil phosphorus measured in the top 10 cm (Colwell). The critical nutrient range was 20-25 mg/kg for the sandy loam soils at Mundulla and 40-50 mg/kg for the black clay and peat soils at Millicent. Nitrogen applications significantly increased seed oil content at 6 sites, significantly decreased it at 2 sites and had no effect at 13 sites. Phosphorus significantly increased seed oil content at only 1 site, significantly decreased it at 3 sites, and had no effect at the other 17 sites.

The residual values of granular reactive rock phosphate (highly carbonate-substituted apatite from North Carolina, USA.), partially powdered low-reactive Queensland rock phosphate (low carbonate-substituted apatite from the Duchess deposit), and granular triple superphosphate were measured in 3 experiments on different lateritic soils in different climatic regions of south-western Australia (Gibson, South Bodallin, West Dale). Finely powdered calcined crandallite-millisite rock phosphate from Christmas Island (Calciphos) was included in one of the experiments. The fertilisers were applied once only in May 1984 and their residual value measured over 3 years (1984-1986) using yield and phosphorus content of the following species each year: experiment 1 (Gibson), barley in years 1 and 2 and oats in the third year; experiment 2 (South Bodallin), triticale in all 3 years; experiment 3 (West Dale), subterranean clover in years I and 2 followed by oats in year 3. Relative to triple superphosphate (TSP) applied each year, the effectiveness of superphosphate in year 1 (year of application) in the experiment at Gibson decreased by about 40% between years 1 and 2, and by a further 5% between years 2 and 3. The corresponding values for the experiment at South Bodallin were 75% and 5%, and at West Dale 50% and 25%. All rock phosphates were much less effective than TSP in year 1, being 5-30% as effective as TSP. Effectiveness of rock phosphates remained low over the 3 years, being 5-20% as effective as newly applied TSP. Although the effectiveness of TSP decreased, it continued to be 50% as effective as newly applied TSP after 3 years. Residual TSP and both freshly applied and residual rock phosphates did not support the same maximum yield as freshly applied TSP despite well defined yield plateaux being obtained in each case. At each harvest, the relationship between yield and phosphorus content of plants was similar for all fertilisers so that the smaller maximum DM and grain yield and reduced effectiveness of the rock phosphates were largely due to less phosphorus being taken up by plants.

Documentation of the chemical fertility status of the soils is sparse for the western and central-western wheatbelt of New South Wales, Australia. We examined properties of the surface soils (0–10 cm) from central-western NSW by collating two published and nine unpublished datasets of soil analyses representing about 2800 soil samples. The emphasis was on the red soils used extensively for cropping. The surface soils of central-western NSW have low phosphorus (47% of soils) and sulfur (70% of soils <5 mg S/kg using KCl-40 analysis) status and commonly have organic carbon contents of about 1%. Surface soil acidity was a substantial problem with 56% of soils (0–10 cm) having a pHCa <5.0. Sodic and dispersive soils are also of concern in this area and these soils have received little attention or research. Approximately 5% of surface (0–10 cm) soils had an exchangeable sodium percentage of ≥6% (sodic). Salinity of surface soils was of minor significance compared with other soil problems in the area, although isolated areas occur. These results indicated that lime applications in this area are likely to benefit crop and pasture production. Additional use of phosphorus and sulfur fertilisers and agricultural practices which increase or maintain organic carbon will also need to be adopted to improve pasture and crop production. The use of gypsum and/or lime on sodic soils may also need to be addressed. As a priority, we suggest that the benefits of lime application to crop yield be examined. The application of lime to the 0–10 cm soil depth should ultimately arrest acidification of the subsurface soil (10–20 cm depth) through downward movement of the lime effect. Further examination of gypsum applications to dispersive sodic soils and the evaluation of sulfur deficiency in the field for pastures and canola are also priority areas of likely agricultural relevance.

In pot experiments, levels of superphosphate incorporated through the whole soil were incubated for 30 days in 2 lateritic soils from south-western Australia at 1 of the following 5 soil water contents: air-dry for 30 days, at field capacity for 10 or 30 days, and flooded for 10 or 30 days. The soils were then air-dried for 30 days and the residual value of the superphosphate relative to freshly applied superphosphate was measured using 30-day-old triticale (x Triticosecale cv. Tyalla) and wheat (Triticum aestivum cv. Gamenya) plants. Soil samples were collected just before sowing from each pot for measurement of bicarbonate-extractable phosphorus (P) levels which were compared with the DM yield of plant tops. For all treatments there was a common relationship between the P concentration (data not shown) or P content in the tops and the DM yield. This shows that the treatments can be considered as different dilutions of the same fertiliser. Less P was taken up by plants as the moisture content and period of contact with moist soil increased, and this limited yield. The effectiveness of superphosphate incubated in dry soil was similar to the effectiveness of freshly applied superphosphate. Incubation in moist soil reduced the effectiveness of superphosphate for plant growth, by about 50% for soils incubated at field capacity and 70% for flooded incubated soils. As calculated from the P content of plant tops, the effectiveness of superphosphate incubated in dry soil was similar to the effectiveness of freshly applied superphosphate, and the effectiveness of superphosphate decreased by about 55% for soils incubated at field capacity and 75% for flooded incubated soils. The amount of P extracted by sodium bicarbonate from soil sampled just before sowing was also influenced by the incubation treatments, and decreased in the following order: freshly applied = air dry incubated > field capacity incubated > flooded incubated. Thus the bicarbonate-soluble P extracted from the soil qualitatively paralleled the yield results. However, compared with the yield results, the decreases were not as marked. When the bicarbonate-extracted P results were compared with subsequent yields of triticale or wheat, separate calibration curves were required for the different incubation treatments.

[Truncated abstract] Eleven sites, each with the trio of land uses: Eucalyptus globulus plantation, pasture and natural vegetation, representing from the Mediterranean climate, high rainfall region (<550 mm annually) of south-western Australia were investigated to assess medium-term changes in the P-supplying capacity of soils in eucalypt plantations growing on agricultural land. The natural vegetation soils were a benchmark for comparing soil P change since land clearing and development for agriculture. The experimental framework provided an ideal basis for studying changes in P forms since land clearing and fertilization for agriculture and the ensuing conversion to plantations (on an average 9 years ago). Conventional soil P indices measure plant available P that is more relevant to short duration annual crops and pastures. To predict medium-term P availability, P forms were determined using Hedley et al.’s (1982) fractionation scheme and fractions were grouped using the Guo and Youst (1998) criteria into readily, moderately and sparingly available P. The P species were also determined by 31P NMR spectroscopy of 0.5M NaOH-0.1M EDTA extracts. Hedley et al.’s (1982) inorganic P extracted by anion exchange resin and by NaHCO3 are widely considered to be approximations to the actual plant available P. The availability to plants of other P fractions is less certain and this is examined in an experiment to compare the plant availability of various P fractions in soils from fertilized and unfertilized land uses following exhaustive cropping in the glasshouse. The soil texture for the sites studied included coarse sand, loamy sand, clayey sand, and sandy loam. Surface soils (0-10 cm) have pH(CaCl2) in the acidic range (mean 4.4) and there is no significant difference due to differences in land use (P<0.05). The soils are of low EC (1:5 H2O) - 6 mS m-1. There is an almost 5-fold variation in organic C among sites (from 1.4% to 8%) but organic C values did not show any significant effect (P<0.05) of changes in land use. To evaluate the degree of similarity of soils within each triplet set at a site principal component analysis was carried out on those soil chemical⁄mineralogical characteristics that were least likely to be affected by changes in land use practices. This analysis showed good matching of the triplet of sub-sites on the whole, especially for the duo of pasture and plantation land uses. This degree of matching of the trio of land uses was considered while interpreting the effects of land use on the forms and behaviour of soil P, and variations due to various extents of mismatch were mostly addressed using statistical techniques including regression analysis to interpret sub-site difference

Low availability of soil phosphorus (P) caused by strong sorption of P is a major constraint to agricultural production in most South African soils, particularly those from the high rainfall areas. The aim of this study was therefore to investigate whether combined addition of goat manure with inorganic P fertilizers could enhance P availability in some P fixing soils of the Transkei region, South Africa. The study addressed the following specific objectives (i) to assess P sorption capacities and requirements of selected soils and their relationship with selected soil properties and single point sorption test, (ii) to assess the effects of goat manure and lime addition on P sorption properties of selected P fixing soils (iii) to assess the temporal changes in concentration of inorganic and microbial biomass P fractions following application of inorganic fertilizer P with goat manure in a laboratory incubation experiment, and, (iv) to assess the effects of goat manure application with inorganic phosphate on inorganic and microbial biomass P fractions, P uptake and dry matter yield of maize. Sorption maxima (Smax) of seven soils examined ranged from 192.3 to 909.1 (mg P kg-1) and were highly and positively correlated with sorption affinity constant (r = 0.93, p = 0.01) and organic C (r = 0.71, p = 0.01). The amount of P required for maintaining a soil solution concentration of 0.2 mg P l-1 ranged from 2.1 to 123.5 mg P kg-1 soil. Soils collected from Qweqwe (a Cambisol), Qunu (an Acrisol), Ncihane (a Luvisol) and Bethania (a Ferralsol) had lower external P requirement values and were classified as lower sorbers, whereas soils from Ntlonyana (a Planosol), Chevy Chase (a Ferralsol) and Flagstaff (a Ferralsol) were classified as moderate sorbers. The results suggested that P availability could be compromised in 43 percent iii of the soils studied and that measures to mitigate the adverse effects of P sorption were needed to ensure that P is not a limiting factor to crop production, where such soils are found. Goat manure addition at varying rates (5, 10 and 20 tha-1 dry weight basis) to two of the moderately P fixing soils from Chevy Chase and Flagstaff, reduced P sorption maxima (Smax) compared to the control treatment. Phosphate sorption decreased with increasing amounts of goat manure in both soils but the extent of reduction was greater on Chevy Chase soil than on Flagstaff soil. The relative liming effects of the different rates of goat manure followed the order 20 t GM ha-1 > 10 t GM ha-1 > 5 t GM ha-1. In a separate experiment, addition of inorganic P at varying rates (0, 90, 180, and 360 kg P ha-1) to Flagstaff soil increased labile P fractions (resin P, biomass P and NaHCO3-Pi) and the increases were greater when goat manure was co-applied. The control treatments contained only 17.2 and 27.5 mg P kg-1 of resin extractable P in the un-amended and manure amended treatments, respectively which increased to 118.2 and 122.7 mg P kg-1 on day 28 of incubation. Biomass P concentration was increased from 16.8 to 43.9 mg P kg-1 in P alone treatments but the fraction was greatly enhanced with manure addition, increasing it from 32.6 to 97.7 mg P kg-1. NaOH-Pi was the largest extractable Pi fraction and ranged from 144.3 to 250.6 mg P kg-1 and 107.5 to 213.2 mg P kg-1 in the unamended and manure amended treatments, respectively. Dry matter yield and P uptake by maize grown in the glasshouse were highly and significantly (p = 0.05) correlated with the different P fractions in the soil. The correlations followed the order resin P (r = 0.85) > NaOH-Pi (r = 0.85) > NaHCO3-Pi (r = 0.84) >> biomass P (r = 0.56) for dry matter yield at 6 weeks after planting. At 12 weeks after planting, goat manure had iv highly significant effects on resin P and biomass P but had no effect on NaHCO3-Pi and NaOH–Pi. The combination of biomass P, resin P and NaHCO3-Pi explained 75.8 percent of the variation in dry matter yield of which 63.0 percent of the variation was explained by biomass P alone. The greatest increase in biomass P occurred when added P was co-applied with 5 or 10 tha-1 goat manure. The predictive equation for maize dry matter yield (DM) was: DM (g) = 1.897 biomass P + 0.645 resin P (r = 0.73). Resin P was the fraction that was most depleted due to plant uptake and decreased by 56 to 68 percent between the 6th week and the 12th week of sampling indicating that it played a greater role in supplying plant available P. The results therefore suggested that the use of goat manure may allow resource poor farmers to use lower levels of commercial phosphate fertilizers because of its effect to reduce soil P sorption. In addition, higher increases in biomass P due to manure addition observed at lower rates of added P indicated that goat manure has potential for enhancing bioavailability and fertilizer use efficiency of small inorganic P applications.

[Truncated abstract] Soils of Western Australian cropping regions are very low in phosphorous. White lupin, chickpea, and faba bean are being increasingly used in rotations with wheat on these soils. Yield of wheat after a legume crop is frequently higher than its yield after wheat. It has been reported that in addition to nitrogen, legumes can also contribute to improve the availability of phosphorous for the subsequent crops. This PhD research project aimed at optimising the economic returns of wheat-legume rotations through more efficient use of P fertiliser in the legume phase as well as enhanced availability of soil P in the subsequent wheat phase

[Truncated abstract] Relationships between the persistence of organic matter added to soil, the dynamics of soil organic carbon (C) and phosphorus (P) were examined in four experiments on lateritic soils of Western Australia. The main objective was to quantify the release of P following organic matter application in soils which have high P adsorbing capacity. Another objective was to confirm that due to its recalcitrant materials, the effect of peat lasted longer in soil than other sources of organic matter in terms of increasing plant-available P fractions. Three experiments were conducted under glasshouse conditions for various lengths of time, with nine- to twelve-month incubations to investigate these hypotheses. As expected, organic matter with lower C:N ratios than peat (lucerne hay) decomposed more rapidly compared with peat, and the most active mineralisation took place within the first three months of incubation. Soil organic-C (extracted by 0.5 M K2SO4) had a significant positive correlation with P extracted with 0.5 M NaHCO pH 8.53. For a higher application rate (120 ton ha-1), peat was better than wheat straw and lucerne hay in increasing extractable bicarbonate-P concentrations in soil, especially at incubation times up to 12 months. Throughout the experiment, peat was associated with a steady increase in all parameters measured. In contrast to peat, nutrient release from lucerne hay and wheat straw was rapid and diminished over time. There was a tendency for organic-C (either in the form of total extractable organic-C or microbial biomass-C) to steadily increase in soil with added peat throughout the experiment. Unlike wheat straw and lucerne hay, extractable organic-C from peat remained in soil and there was less C loss in the form of respiration. Therefore, peat persisted and sequestered C to the soil system for a longer time than the other source of organic matter. Freshly added organic matter was expected to have a greater influence on P transformation from adsorbed forms in lateritic soils than existing soil organic matter. By removing the existing soil organic matter, the effect of freshly applied organic matter can be determine separately from that of the existing soil organic matter for a similar organic-C content. In order to do this, some soil samples were combusted up to 450° C to eliminate inherent soil organic matter. The release of P was greater when organic-C from fresh organic matter was applied to combusted soils than in uncombusted soils that contained the existing soil organic matter. The exception only applied for parameters related to soil micro-organisms such as biomass-C and phosphatase. For such parameters, new soil organic matter did not create conditions favourable for organisms to increase in activity despite the abundance of organic matter available. More non-extractable-P was formed in combusted soils compared to bicarbonate-P and it contributed to more than 50% of total-P. As for the first experiment, peat also showed a constant effect in increasing bicarbonate extractable-P in the soil

Copy of author's previously published work inserted. Bibliography: leaves 147-189. This project examines the uptake of mineral N from the subsoil after anthesis and its effect on grain protein concentration (GPC) of wheat. The overall objective is to examine the importance of subsoil mineral N and to investigate the ability of wheat to take up N from the subsoil late in the season under different conditions of N supply and soil water availability. Greenhouse experiments investigate the importance of subsoil mineral N availability on GPC of wheat and the factors that contribute to the effective utilisation of N. The recovery of N from subsoil, the effect of split N application on GPC and short term N uptake by the wheat at different rooting densities are also studied.

The effects of 40 years of integrated field management on soil organic phosphorus and its forms was evaluated on a highly organic B.C. soil supporting high value vegetable crops. This project was undertaken to study the effects of cultivation on the soil content of organic phosphorus, as a predictor of overall degradation effects of the soil organic matter. Organic carbon, total nitrogen, soil pH and total and inorganic phosphorus were also evaluated, due to the strong relationship of organic P and these other soil chemical properties. The forms of organic P that were evaluated were the phytic acid, inositol polyphosphates and the soil biomass phosphorus. The biomass P was used as a predictor of the effects of cultivation on nucleic acids since the soil methods for nucleic acid determination were very complicated and time consuming. In this study, attempts were made to find a shorter soil analytical method for phytic acid, the largest pool of soil organic phosphorus. Due to chemical structure of phytic acid and its higher negative charge, it was believed that this molecule is highly stable in the soil environment due to its adsorption and/or precipitation on mineral surfaces through cation bridging at low soil pH particularly by Iron and Aluminium salts and hydrous oxides which bear pH-dependent positive charge or through P chermsorption, and hence its turnover rate due to cultivation could be used to predict the behaviour of the rest of soil organic P and hence the organic matter in the same soil environment. It was however realized that P analysis in soils was very cumbersome and there was a need for a shorter and precise quantitative analytical technique for this element in the soil. ³¹P NMR spectroscopy was thought to be the solution and its possibilities were evaluated in this project. Therefore the objectives of the study were; a) To determine the effects of 40 yrs of integrated field managements on organic P and its forms. b) To develop a shorter method for soil phytic acid analysis. c) To attempt the use of ³¹P NMR for qualitative and quantitative determinations of soil phytic acid. It was found that soil pH was significantly increased from pH 4.46 to 5.28 due to liming and the increased degree of organic matter decomposition. Total nitrogen was significantly decreased by 24% with larger significant decrease of 42% in the shallow organic cultivated soil site, and only 8% significant decrease in the highly organic, deeper cultivated soil site. The decline in soil nitrogen was attributed to mineralization of organic nitrogen followed by crop uptake and leaching losses. Organic carbon was significantly decreased by 22%. There was a 40% decrease in this organic carbon in the cultivated shallow organic cultivated soil site, but there was no significant effect of cultivation on organic carbon (hence the organic matter) in the highly organic deeper cultivated soil site. There was no significant effect of cultivation on the C/N ratio. However, the highly organic deeper soil site had significantly wider C/N ratio than the shallow organic cultivated soil site. This observation was attributed to the degree of decomposition of soil organic matter in the two sites. There was a significant 20% decrease in P total in the highly organic deeper cultivated soil site. There was no significant effect of cultivation on P total in the shallow organic cultivated soil site, however there were indications of 33% accumulation in total P in this soil site as determined by ignition method. There was 179% accumulation of inorganic P in the shallow organic cultivated soil site, but there was no significant effect of cultivation on inorganic P in the deeper highly organic soil cultivated site. Organic phosphorus was significantly decreased by 4 0 yrs of integrated field management by 31% on a soil basis and 25% on an ash free basis. The percentage of organic P in total soil P was significantly decreased from 66% to 45%. The C/orgnic P was increased significantly from 394 to 439. This reflected greater effects of cultivation on turnover of organic P than organic carbon in the organic matter and that P has a geological cycle which organic carbon does not have. The results further showed that before the field was placed under cultivation, the shallow organic soil site had a significantly larger amount (73%) of organic P in the soil total P. However cultivation had a significant decrease in organic P by 23% in the deeper highly organic soil cultivated site and 40% in the shallow organic cultivated soil site. The study soil sites started with same the amounts of biomass P (the most labile form of organic P) , however it was found that 40 years of cultivation had no significant effects on this biomass in the highly organic soil site, but there was a significant decrease in biomass P by 86% in the shallow organic cultivated soil site. Soil phytic acid, the largest pool of organic P was significantly decreased by 28% due to 40 yrs of integrated field management. Its turnover rate was found to be equal to the turnover rate of the other forms of organic P. It was however noted that the study soil sites started with same amount of phytic acid before the field was placed under cultivation. Phytic acid was significantly decreased due to cultivation in the shallow organic cultivated soil site by 35%, but there was no significant effect of cultivation on phytic acid in the highly organic cultivated soil site. Inositol polyphosphates were not significantly affected by 40 years of integrated management. This form of organic P was found to have the same turnover rate as the rest of soil organic P. The slower turnover rate of inositol polyphosphates assayed by the barium acetate precipitation method of McKercher and Anderson was attributed to methodology. In the present study, there were no significant differences in results obtained by various methods for total P determination except in a few cases where the ignition method was thought to have over-estimated total P. A tentative new method for phytic acid analysis was developed in the on-going research. This method was proposed to be applicable in all soils. However, further research is required to confirm the purity of the phytic acid determined by this method. ³¹P NMR spectroscopy showed potential possibility for qualitative and quantitative analysis of soil phytic acid. However, it was emphasized that care should be exercised particularly during sample concentration step. It was concluded that organic P and its forms, organic carbon, total nitrogen, soil pH and phytic acid were significantly decreased by 40 years of integrated field management more in the shallow organic cultivated soil sites than in the deeper highly organic soil sites. This observation was found very interesting and was in contrast to existing soil literature and further research was proposed in this direction to investigate this phenomenon.
Land and Food Systems, Faculty of
Graduate

Bibliography: leaves 164-193. This study aims to quantify the belowground input of organic carbon by barrel medic using techniques that account for root death and decomposition as well as root secretion and exudation. It also investigates the effect of defoliation on carbon allocation within the plant so as to determine the potential for optimising carbon input to the soil through grazing management.

Bibliography: leaves 131-153. This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels.