Thesis (MSc. Agriculture (Soil Science)) -- University of Limpopo, 2014 / Phosphorus (P) runoff from agricultural sites and the subsequent loading into surface water bodies contribute to eutrophication. Environmental concerns associated with P loading in soil have motivated the need for the development of a proper tool that will allow farmers to identify agricultural areas or management practices that have the greatest potential to accelerate eutrophication. The objective of the study was to determine the spatial variability of soil test P, soil loss potential of the farm, P application rate and methods, and map P runoff risk across the field. This study was conducted in Vierfontein Boerdery in Kriel, Mpumalanga province, South Africa (longitude 29.11258833 and latitude -26.27104340). The field was under dryland cultivation and planted to yellow maize that was rotated with soybeans. Soil samples were taken at georeferenced locations in a 100 x 100 m grid for soil analysis. Spatial layers of soil P distribution, soil loss potential as well as application rate and method were created in ArcGIS software. These layers were used as input factors in a P index model to identify areas in the farm that are vulnerable to P runoff. Results indicated a variation in soil test P. Although soil test P variation was not statistically different at P≤0.05, variation had both agronomic and environmental implications. This variation could be attributed to differences in site-specific conditions and management practices. Furthermore, soil loss potential across the study site predicted by the Revised Universal Soil Loss Equation (RUSLE) showed variation with a range of 3-15 tons/ha/yr. This variation was attributed to differences in topographic variations in the study site. There is a need for best management practices that control soil erosion to minimize P runoff into water bodies. KEYWORDS: Eutrophication, Geographic Information System, Phosphorus best management practises, Phosphorus runoff index, Soil erosion, Site-specific management.

The application of substantial quantities of phosphorus (P) has been required to increase productivity on many Australian soils. Unfortunately, these applications have often resulted in increased concentrations of P in surface runoff that contributes to excessive algal growth in surface waters and consequently a decline in their quality. The concentrations of P in runoff from intensively managed pastures are often high (1-5 mg/L) and typically at least an order of magnitude higher than water quality targets. Although a substantial amount of research has been devoted to the problem of P accumulation and mobilisation in arable systems ( in which P is typically mobilised by the action of raindrop impact and subsequently transported in particulate form ), there has been substantially less research in intensively managed pasture systems. Consequently, there is a paucity of knowledge concerning the fundamental processes and factors responsible for P in runoff from these systems and a dearth of truly effective remedial strategies. In this thesis, the accumulation of P in soil under intensively managed pastures used for dairying and the processes responsible for its mobilisation in surface runoff were investigated. This research was undertaken at two research sites in South - east Australia, i.e. Camden in New South Wales and Flaxley in South Australia. A number of factors relating to scale and hydrology may influence the processes of P mobilisation and its concentration in runoff. A comparison was made of the forms and concentrations of P in runoff between a typical rainfall simulation methodology and large runoff plots. The effect of rainfall intensity on the forms and concentrations of P was also investigated. The concentrations of P in runoff from small - scale, high - intensity rainfall simulations were on average 33 % lower than those from large plots ( approximating hillslopes ) although the processes of mobilisation ( as evidenced by runoff P forms ) were similar. Increasing rainfall intensity resulted in decreasing P concentrations, but similar forms of P. It was hypothesised that changes in hydrological characteristics ( residence time and depth of runoff ) were responsible for the differences in the P concentrations. A model of P mobilisation ( incorporating hydrological and P - release characteristics ) was developed and shown to successfully predict runoff P concentrations under a range of rainfall intensities. These findings and the subsequent model were used in the successful modelling of landscape scale nutrient exports based on rainfall simulation data as part of a separate, but complementary project. There is anecdotal evidence to suggest that Australian soils are relatively ' leaky ' in terms of P in runoff compared to soils overseas. Consequently, comparisons of the labile soil P characteristics and soil P - runoff P relationships were made between Australian soils and soils of similar fertility from the USA, UK and New Zealand ( using both experimental data and data sourced from the literature ). It was concluded that Australian soils leak more P than soils of similar fertility in the USA, UK and New Zealand, although it was beyond the scope of the thesis to make more detailed comparisons between Australian and overseas soils. The accumulation and mobilisation of P in two soils used for intensive pasture production in Australia were investigated. In intensive pasture systems P accumulated in the shallowest zones of the soil and principally as inorganic P. The concentrations of labile P were 3 - 5 times higher in the top 0.01 m than in the top 0.1 m. Using a simple model, it was estimated that only the top several mm of soil influence runoff P concentrations. The dominant form of P in runoff was shown to be orthophosphate although in low to moderate fertility soils, dissolved organic P can constitute a substantial proportion of the P in runoff. These results confirm the need to reduce the pool of P available for mobilisation in the immediate topsoil in order to reduce runoff P concentrations. Because P is stratified, it was hypothesised that one method to reduce the pool of P available for mobilisation is to de - stratify the soil ( i.e. mix the topsoil ). The effect of this technique on runoff P concentrations was investigated in laboratory and rainfall simulation experiments. These experiments revealed that reductions in runoff P concentrations between 45 and 70 % can be achieved by de - stratification of soils under permanent pastures. It was hypothesised that the benefits of de - stratification could be maximised using a combination of information relating to catchment hydrology and the spatial distribution of soil P and that this would result in large reductions in P exports with a relatively small degree of inconvenience to land managers. Given the limited opportunities identified in previous research to reduce P exports in runoff, the strategic utilisation of de - stratification is a potentially important option in water quality management for the dairy industry and warrants further investigation. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2006.

The application of substantial quantities of phosphorus (P) has been required to increase productivity on many Australian soils. Unfortunately, these applications have often resulted in increased concentrations of P in surface runoff that contributes to excessive algal growth in surface waters and consequently a decline in their quality. The concentrations of P in runoff from intensively managed pastures are often high (1-5 mg/L) and typically at least an order of magnitude higher than water quality targets. Although a substantial amount of research has been devoted to the problem of P accumulation and mobilisation in arable systems ( in which P is typically mobilised by the action of raindrop impact and subsequently transported in particulate form ), there has been substantially less research in intensively managed pasture systems. Consequently, there is a paucity of knowledge concerning the fundamental processes and factors responsible for P in runoff from these systems and a dearth of truly effective remedial strategies. In this thesis, the accumulation of P in soil under intensively managed pastures used for dairying and the processes responsible for its mobilisation in surface runoff were investigated. This research was undertaken at two research sites in South - east Australia, i.e. Camden in New South Wales and Flaxley in South Australia. A number of factors relating to scale and hydrology may influence the processes of P mobilisation and its concentration in runoff. A comparison was made of the forms and concentrations of P in runoff between a typical rainfall simulation methodology and large runoff plots. The effect of rainfall intensity on the forms and concentrations of P was also investigated. The concentrations of P in runoff from small - scale, high - intensity rainfall simulations were on average 33 % lower than those from large plots ( approximating hillslopes ) although the processes of mobilisation ( as evidenced by runoff P forms ) were similar. Increasing rainfall intensity resulted in decreasing P concentrations, but similar forms of P. It was hypothesised that changes in hydrological characteristics ( residence time and depth of runoff ) were responsible for the differences in the P concentrations. A model of P mobilisation ( incorporating hydrological and P - release characteristics ) was developed and shown to successfully predict runoff P concentrations under a range of rainfall intensities. These findings and the subsequent model were used in the successful modelling of landscape scale nutrient exports based on rainfall simulation data as part of a separate, but complementary project. There is anecdotal evidence to suggest that Australian soils are relatively ' leaky ' in terms of P in runoff compared to soils overseas. Consequently, comparisons of the labile soil P characteristics and soil P - runoff P relationships were made between Australian soils and soils of similar fertility from the USA, UK and New Zealand ( using both experimental data and data sourced from the literature ). It was concluded that Australian soils leak more P than soils of similar fertility in the USA, UK and New Zealand, although it was beyond the scope of the thesis to make more detailed comparisons between Australian and overseas soils. The accumulation and mobilisation of P in two soils used for intensive pasture production in Australia were investigated. In intensive pasture systems P accumulated in the shallowest zones of the soil and principally as inorganic P. The concentrations of labile P were 3 - 5 times higher in the top 0.01 m than in the top 0.1 m. Using a simple model, it was estimated that only the top several mm of soil influence runoff P concentrations. The dominant form of P in runoff was shown to be orthophosphate although in low to moderate fertility soils, dissolved organic P can constitute a substantial proportion of the P in runoff. These results confirm the need to reduce the pool of P available for mobilisation in the immediate topsoil in order to reduce runoff P concentrations. Because P is stratified, it was hypothesised that one method to reduce the pool of P available for mobilisation is to de - stratify the soil ( i.e. mix the topsoil ). The effect of this technique on runoff P concentrations was investigated in laboratory and rainfall simulation experiments. These experiments revealed that reductions in runoff P concentrations between 45 and 70 % can be achieved by de - stratification of soils under permanent pastures. It was hypothesised that the benefits of de - stratification could be maximised using a combination of information relating to catchment hydrology and the spatial distribution of soil P and that this would result in large reductions in P exports with a relatively small degree of inconvenience to land managers. Given the limited opportunities identified in previous research to reduce P exports in runoff, the strategic utilisation of de - stratification is a potentially important option in water quality management for the dairy industry and warrants further investigation. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2006.

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.

Thermal desorption (TD), a remediation method used to remove hydrocarbons from contaminated soils, may cause changes in soil properties that threaten soil function and plant productivity. The goal of this research is to better understand the effect that TD treatment has on soils intended for agricultural use. A series of soil phosphorus (P) sorption and desorption experiments were conducted on soils before and after TD treatment to determine P availability for plant uptake and risk for run-off. TD-treated soils retained more P, likely due to mineral transformations of Fe- and Al-oxides. In addition, a three-year field study using mixtures of topsoil (A), crude-contaminated soil (SP), and TD-treated soils (TDU) was conducted. Yields were significantly greater in plots that included A in the mixture compared to SP and TDU soils alone. TD-treated soils can be a replacement for topsoil, but the addition of topsoil will reduce the time to successful reclamation.

Thesis (PhD(Agric) (Agronomy))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Continuous cropping without replenishing the nutrient component of soils will eventually lead to the depletion of soil nutrients. Small scale farmers in Zimbabwe often do not have the financial means to buy fertilizer and this problem is exacerbated by scarcity of commodities such as fertilizers. The use of herbaceous legumes such as mucuna (Mucuna pruriens) can assist to recapitalize soil fertility depletion and improve subsequent maize productivity in sandy loam soils in the small holder farming sector of Zimbabwe. In this study the effect of phosphorus (P) application to a mucuna crop, the effect of mucuna management options and the application of nitrogen (N) to the subsequent maize crop was investigated. The experiment was carried out during the 2007 to 2009 seasons at the Grasslands Research Station in Marondera in Zimbabwe. The soils are classified as humic ferrolsols and are predominantly of the kaolinitic order with sandy loams of low fertility and are slightly acid (pH CaCl = 5.2). A randomized complete block design was used for the effect of P on mucuna productivity and the effect of P and mucuna management options on the soil properties. The treatments were two P rates (P0 and P40 = 0 kg P ha-1 and 40 kg P ha-1 respectively) applied to a preceding mucuna crop, four mucuna management options [1) fallow (F) (no mucuna planted = control), 2) mucuna ploughed-in at flowering (MF), 3) all mucuna above ground biomass removed at maturity and only roots were ploughed-in (MAR) and 4) mucuna pods removed and the residues ploughed-in (MPR)]. A split-plot design was used to study the effect of P application to mucuna, mucuna management options and N rates on the growth and yield of the subsequent maize crop. The four N treatments [N0 = 0 kg N ha-1, N40 = 40 kg N ha-1, N80 = 80 kg N ha-1 and iv N120 = 120 kg N ha-1] were applied to a subsequent maize crop. Growth and development parameters such as biomass production, leaf area index, nutrient content of the foliage and grain yield were determined in the mucuna and maize crops. Soil parameters investigated included nutrient content, pH, bulk density and porosity. Phosphorus application in these particular soil conditions positively influenced mucuna biomass production and therefore enhanced the role of mucuna as a rotational crop by increased positive effects on the subsequent maize crop. The incorporation of above-ground biomass of mucuna had positive effects on all soil properties investigated. The MF and MPR management options increased the soil organic matter (OM) and reduced bulk density which leads to an improvement in porosity (f) of the soil. Mucuna incorporated at flowering (MF) and P40 treatment combination resulted in the highest mineral N, P, potassium (K), calcium (Ca) and magnesium (Mg) levels. A significant three-way interaction (P<0.05) between mucuna management options, nitrogen rates and time was observed in terms of biomass production and all nutrients in the leaves of the subsequent maize crop. The main findings were that the MF management option had the highest biomass and foliar nutrient accumulation through-out all the treatment combinations. In general the MF management option gave the highest maize yield across all the treatment combinations. Incorporation of mucuna biomass into the soil prior to planting a maize crop therefore improve soil physical and chemical qualities resulting in improved soil conditions for a subsequent maize crop which in turn lead to higher maize yields. Including a mucuna rotational crop have a similar effect on maize yield than application of 80 kg ha-1 of fertilizer N. / AFRIKAANSE OPSOMMING: Aanhoudende verbouing van gewasse op dieselfde grond sonder om voedingstowwe aan te vul lei uiteindelik tot die agteruitgang van die grond se vrugbaarheid. Kleinboere in Zimbabwe het meestal nie die finansiële vermoëns om bemestingstowwe te koop nie en die probleem word vererger deur die onbekombaarheid van kommoditeite soos bemestingstowwe. Die gebruik van kruidagtige peulplant gewasse soos mucuna (Mucuna pruriens) kan bydra om grondverarming teen te werk en om die produksie van ‗n daaropvolgende mielie aanplanting in sandleemgronde in ‗n kleinboerstelsel in Zimbabwe te verhoog. In hierdie studie is die invloed van fosfor (P) toediening aan ‗n mucuna aanplanting, die invloed van bestuursopsies van die mucuna en die toediening van stikstof (N) aan die daaropvolgende mielie aanplanting ondersoek. Die eksperiment is tydens die 2007 tot 2009 reënseisoen by die Grasslands Research Station in Marondera in Zimbabwe uitgevoer. Die grond word geklassifiseer as humiese ferrolsols en is hoofsaaklik sanderige leemgrond van die kaolinitiese orde met lae vrugbaarheid en is effens suur (pH CaCl = 5.2). ‘n Volledig ewekansige blokontwerp is gebruik om die invloed van P op die produktiwiteit van mucuna te bepaal asook die invloed van P toediening en mucuna bestuursopsies op grondeienskappe. Die behandelings was twee P vlakke (P0 = 0 kg P ha-1 en P40 = 40 kg P ha-1) wat aan ‗n voorafgaande mucuna aanplanting toegedien is, vier mucuna bestuursopsies [1) braak (F) (geen mucuna geplant = kontrole), 2) mucuna ingeploeg met blomtyd (MF), 3) alle bogrondse mucuna biomassa verwyder by rypwording en slegs wortels ingewerk (MAR) en 4) mucuna peule verwyde en die res van die bogrondse material ingeploeg (MPR)] en vier N behandelings [N0 = 0 kg N ha-1, N40 = 40 kg N ha-1, N80 = 80 kg N ha-1 en N120 = 120 kg N ha-1] toegedien aan ‗n daaropvolgende mielie aanplanting. Groei en ontwikkeling parameters soos biomassa produksie, blaaroppervlakindeks, nutriëntinhoud van die blare en graanopbrengs is in die mucuna en mielie aanplantings ondersoek. Grondeienskappe soos nutriëntinhoud, pH, bulkdigtheid en porositeit is gemeet. Fosfaat toediening aan hierdie spesifieke grondtipe het mucuna produksie positief beïnvloed en dus die rol van mucuna as rotasiegewas verbeter deur positiewe reaksies in die daaropvolgende mielie aanplanting. Die inwerk van bogrondse mucuna biomassa het al die fisiese grondeienskappe wat ondersoek is positief beïnvloed. Die MF en MPR bestuursopsies het organiese materiaal inhoud van die grond verhoog en bulkdigtheid verlaag wat lei tot verbeterde grondporeusheid (f). Mucuna wat tydens blomvorming ingewerk is (MF) lei tot die hoogste minerale N, P, kalium (K), kalsium (Ca) en magnesium (Mg) vlakke. ‗n Betekenisvolle drie-rigting interaksie (P < 0.05) tussen mucuna bestuursopsies, N vlakke en tyd is waargeneem in terme van biomassa produksie en in terme van al die nutriëntvlakke in die mielieblare wat ondersoek is. Die hoofbevindinge was dat die MF bestuursopsie die hoogste biomassa produksie en blaarnutriënt akkumulasie oor alle behandelingskombinasies tot gevolg gehad het. In die algemeen het die MF bestuursopsie die hoogste mielie-opbrengs oor alle behandelingskombinasies tot gevolg gehad. Die inwerk van mucuna materiaal in die grond voordat mielies geplant word verbeter dus fisiese en chemiese toestande in die grond wat grondtoestande verbeter vir die daaropvolgende miegewas en uiteindelik lei tot hoër mielie-oeste. Die insluiting van mucuna as ‘n rotasiegewas het diesefde effek op mielie-opbrengs as die toediening van 80 kg ha-1 N bemesting.

In Mediterranean-type climates, topsoil frequently dries out during spring. Problems associated with reduced nutrient (P, K) availability in dry topsoil may be overcome by placing fertilisers deeper in the soil, where the soil is more likely to remain moist for longer periods as opposed to conventional fertiliser placement. Deep-P placement has resulted in significant yield improvements for lupin crops in Mediterranean environments because lupin crops generally require soil P supply during spring (throughout the flowering stage); in contrast, wheat yields have seldom improved with deep P placement, presumably because plants have accumulated sufficient P prior to spring (grain filling stage) for maximum grain yields. The P and K accumulation patterns of canola had not been investigated, and therefore any potential yield benefits of deep placed fertilisers were unknown. This study aimed to define the P and K demands of canola throughout the growing season, and assess the viability of deep placement of fertiliser in matching soil P and K supply to crop demand. The study further investigated the impact of deep placement of P fertiliser on root growth and distribution throughout the soil profile. Initial glasshouse studies compared the P and K accumulation patterns of several canola cultivars with wheat, and found that the P and K demand of canola continued until later into the season than wheat, but there was little difference in the P and K accumulation patterns of the various canola cultivars. Further experiments in sand culture determined that regardless of the level of K supply, canola plants had accumulated sufficient K for maximum seed yields by early flowering. Under high P supply, canola plants had accumulated enough P for maximum seed yields by early flowering, but when P supply during vegetative growth was just adequate, plants required a continual P supply until mid silique-filling to attain maximum yields. Because plants had accumulated sufficient K for maximum seed yields by early flowering (therefore topsoil drying in spring was unlikely to affect yields), further field experiments examined only deep placement of P fertiliser to improve P uptake and yields.

A greenhouse study was carried out to investigate the effectiveness of soil-applied silicon (Si) with that of foliar applications for sorghum growth. Silicon sources were soil-applied as calmasil (calcium silicate) at two rates (4 and 8t/ha) and foliar applied Si including pure K-silicate, K-humate and K-fulvate (all three foliar treatments at rates of 300 and 600 ppm). Another treatment included soil applied calmasil plus low rate of foliar applied K-humate. The soils used for the greenhouse trial were Cartref, Glenrosa, Nomanci and Fernwood. Results indicated that application of calcium silicate to the soil before planting increased sorghum yield and Si uptake in three of the four soils. Silicon uptake from different experimental treatments followed the order: Calmasil 8t/ha > calmasil 4t/ha ~ calmasil + 300 ppm K-humate> K-humate = K-fulvate = pure-K silicate = control. Foliar sprays were ineffective at increasing yield, Si content of the plant tissues or Si uptake. The concentrations of exchangeable Ca, Mg as well as soil pH were significantly increased by calmasil treatments. Extractable AI concentrations were also reduced due to the Iiming effect of calcium silicate and also possibly formation of insoluble aluminosilicates. The yield response to applied calmasil seemed to be primarily related to its Iiming effect and reductions in extractable AI in the Cartref, Glenrosa and Nomanci soils. The dry matter yield was highest in Fernwood and lowest in Cartref soil. However, there was no significant yield response to calmasil in Fernwood soil which had an initial pH of 5.8 and insignificant extractable AI concentrations. Therefore application of calcium silicate had no significant effect on extractable AI concentration in this soil. Yield response to calmasil may also have been partly due to direct positive effects of applied Si on crop growth through mechanisms such as increased photosynthetic rate and reduced transpiration rate, Addition of calmasil increased the concentrations of Si in the plant tissues and reduced those of N, P and Kin Nomanci and Fernwood soils respectively. This indicates that nutrient interactions were occurring in the plant. It was concluded that foliar-application is not an effective way of applying Si to a Siresponsive crop such as sorghum when growing in soils low in extractable soil Si. This is because Si is accumulated in plant tissues in similar amounts to macronutrients. It was also concluded that in future, studies of crop response to applied Si should include the use of non-Iiming source of Si (e.g. silicic acid) so as to separate a liming effect of calcium silicate from effect of applied Si. In a laboratory study, the effects of applied silicic acid, calcium silicate and calcium hydroxide on levels of extractable P in two Si-deficient soils were investigated. Two soils (Fernwood and Nomanci soils) were treated with two rates of P and three soil amendments (calcium silicate, calcium hydroxide and silicic acid) and incubated for six weeks at room temperature. Phosphorus was extracted using Truog, AMBIC and resin methods, and levels of exchangeable and solution AI and extractable and solution Si were also measured. Application of calcium silicate and calcium hydroxide increased soil pH in both soils while silicic acid additions had no significant effect compared with the control. The pH increase was much greater in the Fernwood than Nomanci soil because of the low buffering capacity of the sandy Fernwood soil. Exchangeable AI and concentrations of monomeric and total AI in soil solution generally followed the order: control ~ silicic acid> calcium silicate> calcium hydroxide. The lowering of soluble AI concentrations in the silicic acid treatments was attributed to formation of insoluble aluminosilicate compounds while that in the calcium silicate and calcium hydroxide treatments was attributed to their Iiming effects causing a rise in pH. Concentrations of Si in soil solution were lower in the calcium hydroxide than the control treatment suggesting the solubility of Si decreased with increased pH. Additions of both Si sources increased Si concentrations in solution and the effect was more marked for the calcium silicate treatment. This was attributed to formation of insoluble aluminosilicates in the silicic acid treatment. Concentrations of H2S04extractable Si with treatment did not closely follow the same trends as those for Si concentrations in soil solution. That is, levels of extractable Si were very much higher in the calcium silicate than silicic acid treatment in both soils. In addition, concentrations of extractable Si in the calcium hydroxide treatment were similar to control in the Nomanci soil, while for the Fernwood soil, concentrations in the calcium hydroxide treatment were exceptionally high. It was suggested that liming with calcium silicate or calcium hydroxide had rendered some Si-containing compounds in the soil acid-extractable and that the nature of acid-extractable Si fraction need further study in future. The quantities of P extracted from the two soils by the various extractants followed the order: Truog> AMBle> resin. The greatest increase in extractable P induced by additions of P was recorded for Truog P and the least for resin P. The effects of Iiming (addition of calcium silicate or calcium hydroxide) on extractable P levels differed depending on the soil and extractant used with increase, decrease or no effect being recorded. Such results confirm the complexity of lime and P interactions which occur in acid soils. Additions of silicic acid had no effect on levels of extractable P, compared to control. It was suggested that the reason for this was that phosphate is adsorbed to AI and Fe oxide surfaces much more strongly than silicate. As a result, additions of Si are ineffective at increasing extractable P levels. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Baby spinach (Spinacia oleracea L.) is considered to be the one of the extremely nutritious vegetables, rich both in phytochemicals and core nutrients. Nowadays, phytochemicals in plants are raising interest in consumers for their roles in the maintenance of human health. Variation in content of bioactive compounds and core nutrients is the main concern in vegetable production. Factors such as cultural practices specially fertilization, may affect the nutritional and medicinal properties of the plants Therefore, three parallel trials for NPK to investigate the response of baby spinach leaves to nitrogen (N), phosphorus (P) and potassium (K) on chemical composition were conducted, with treatments arranged as follows: 0, 45, 75, 105, 120 kg·ha-1 N and P and 0, 60, 85, 106, 127, 148 kg·ha-1 K in a randomized complete block design (RCBD) with four replications. The results demonstrated that, application of nitrogenous, phosphorus, potassium fertilizers significantly increased the total phenolic content, total antioxidant activity, total flavonoid content and vitamin C while magnesium, iron, zinc and selenium did not exhibit significant response to all treatments applied. The increase in concentrations on total phenolic content, total antioxidant activity, total flavonoid content and vitamin C was observed, reaching maximum at 45 kg·ha-1 N, 75 kg·ha-1 P and 85 kg·ha-1 K. The optimum rates of 45 kg·ha-1 N, 75 kg·ha-1 P, 85 kg·ha−1 K were then used to formulate the NPK treatment combinations as follows: 0, 30: 30: 40, 45:45:60, 60:60:70, 75:75:90 kg·ha-1, arranged in a RCBD with three replicates. The results showed that total phenolic content, total antioxidant activity , total flavonoid content and vitamin C reached maximum in baby spinach leaves at N45:P45:K60 kg·ha-1 / Agriculture,  Animal Health & Human Ecology / M.Sc. (Agriculture)

Phosphorus (P) is an essential plant nutrient that may limit plant growth and agricultural productivity if not available for crop plant uptake in sufficient quantities at the time required. Many Australian soils are deficient in available P, despite a long history of P fertilizer application, and this is due to fertilizer P rapidly becoming unavailable largely through biochemical fixation. The resulting low P fertilizer efficiency, coupled with rapidly rising cost of fertilizers, has increased interest in biological cycling of P from sources such as crop residues. However, to date, much of the Australian research has focussed on soils with relatively high organic matter content (> 2%) and relatively heavy texture i.e. medium to high clay content. Furthermore, although there is information on pasture residue decomposition and P release for sandy soils with low organic matter in Australia, a recent shift to continuous cropping systems means that information for a range of crop residues is required but is not currently available. Therefore the aims of the work described in this thesis were to (i) increase the efficiency of P use when crop residue P are applied to crops and (ii) determine the effect of crop residue biochemical quality on decomposition rates, soil P dynamics and plant P uptake in light textured sandy soils with low organic matter which are typical of a large proportion of the southern Australian wheat growing area. A further aim was to investigate the effects of combined additions of plant residue and P fertilizer on P cycling in these soils, a scenario highly relevant to farming systems. A series of soil incubation and plant growth experiments were undertaken to characterize P dynamics in soil following addition of a wide range of crop residues (total 15) collected from agricultural sites throughout South Australia. The residues, differing in age and biochemical quality, were young shoots of canola, lupin, pea, lucerne and lentil; mature shoot residues of canola, lupin, pea and wheat and mature root residues of wheat, canola and lupin. The concentration of total and water soluble P, C, and N in the residues was measured using standard wet chemical analyses and the carbon chemistry was determined by NMR spectroscopy. Decomposition of crop residues was continuously monitored over a period of up to 140 days by measuring soil respiration. Available P and microbial biomass P and C were also assessed at different times during the incubations. The total P in residues ranged from 0.16% to 0.32% and 0.05% to 0.08% in young and mature shoots, respectively. Water-soluble P was related to residue total P and ranged from 29% to 81% and 13% to 29% of total P in young and mature shoots, respectively. The C: P ratio ranged from 133: 1 to 253: 1 and 504: 1 to 858: 1 in young and mature shoots, respectively. Phosphorus availability and microbial P uptake differed between soils amended with crop residues and soluble P fertilizer as triple super phosphate (TSP). Soil respiration rates were significantly higher in soils amended with crop residues than in the soils amended with TSP or the unamended control in the first 58 days of incubation. In an experiment in which residues and TSP were added at a rate of 10 mg P kg⁻¹, available P was greater for TSP than residue-amended soil, whereas microbial P showed the opposite trend. Respiration rate and microbial P were positively correlated with C addition rate, which was highest in mature wheat residue because it had the lowest P concentration. In order to assess when P released from the residues is available for plants, wheat was grown over three consecutive crop periods with each period lasting for 4 weeks. Young residues with high content of water soluble P, C, N and amide and low lignin and phenolic content decomposed faster than mature residues. The C type and amount added with residues controlled the dynamics of P availability. Surprisingly, canola mature root increased available P and plant growth as much as young shoot residues while root residues of wheat and lupin resulted in P immobilization and low plant growth. Compared to canola young shoot, canola mature root has a higher total P concentration and a lower C: P ratio. Plant P uptake was positively correlated with residue total and water-soluble P content and negatively correlated with residue C: P and C: N ratio and amount of C added with the residues. In another experiment where residue was added at 2.5 g C kg⁻¹ soil and compared with TSP (4 and 10 mg P kg⁻¹ soil), available P and plant P uptake decreased in the following order: TSP-10P > canola root ≥ young shoot ≥ TSP-4P > control > mature shoot. Microbial P was greater with residue addition than with TSP and in the control. Residues with low total P and high C: P ratio resulted in P immobilisation in the microbial biomass. Therefore, residues with high total P and low C: P ratio can be an important source of P for plants. Net P immobilisation of mature wheat residues (0.07% P) was significantly reduced by combining wheat residue (C: P ratio 615: 1) with TSP leading to a C: P ratio of 155: 1 to 310: 1. Furthermore, the combination of wheat residue with TSP increased available P in residue and TSP-amended soils by 3.0 mg P kg⁻¹ soil, which was shown to be sufficient to support wheat growth in the early stages of development in the other experiments. Although water-soluble P fertilizers provide plants with immediately available P, a large proportion becomes unavailable over time. Addition of low C: P residues on the other hand, may not result in high amounts of immediately available P, but the P supply is more sustained due to P release from decomposing residues and turnover of microbial biomass P. Phosphorus immobilization after addition of residues which have high C: P ratio (615: 1) may be offset when residue is applied together with inorganic P fertilizer if the resulting C: P ratio is 300: 1 or less. Overall, this study has highlighted the potential role that crop residues, either alone or in combination with inorganic P, can play in increasing P availability in the light textured, low organic matter, P-limited soils typical of many southern Australian farming systems. The results provide important quantitative information on the potential of a wide range of crop residues to supply wheat with P, and how additions of inorganic P interact with residue decomposition and influence available P supply. This quantitative information will be valuable for the construction or validation of mechanistic models of residue decomposition relevant to low organc matter light textured soils in farming systems of southern Australia, and will ultimately assist in the development of economic management strategies for minimizing P fertilizer inputs and maximizing the benefits of biological cycling of P. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2009