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Item An investigation on the effects of lime and/or phosphorus fertilizer applications on soil organic matter preservation : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Manawatu, New Zealand(Massey University, 2021) Li, YangThe poor understanding of the mechanisms through which soil organic matter (OM) is lost with ongoing land-use intensification hampers the development of food security and climate-smart agricultural management practices. The overall objective of this thesis was to investigate the effect of lime and/or phosphorus (P) amendment on OM preservation in a volcanic soil classified as an Andosol – the mineral soil group with the largest organic carbon (OC) content worldwide and characterised by its abundance in aluminium (Al)-OM complexes (e.g., Al³⁺-OM and allophane-OM complexes). Special attention was paid to the response of OM stabilisation and mineralisation with depth to these amendments. Firstly, we hypothesised that (i) lime and P application has an impact on OM stabilisation through different mechanisms, and (ii) their effect is synergic. To have a direct understanding of the effect of lime and/or P application on OM preservation in the Andosol under study, we conducted a batch of water extractions. We extracted the bulk soil and its heavy fraction (>1.6 g/cm3, indicative of the presence of OM-mineral associations) with added lime and/or P to reveal the individual and combined influence of lime and P amendments on water-extractable OM (WEOM), which has been deemed to be an indicator of OM destabilisation. The results obtained from quantitative analyses of WEOM showed that adding lime and/or P significantly increased the WEOM, along with a decrease in its carbon (C)/nitrogen (N) ratio (C/N) and an increase in its aromaticity. The chemical composition of WEOM measured by pyrolysis-gas chromatography/mass spectrometry suggested that lime and P addition (at high application rate) caused an enrichment in WEOM in the poly- and monophenolic, and nitrogenised fraction, as well as in plant-derived polysaccharides. If we consider the effect on the heavy fraction, the increase in WEOM was still consistent with that observed in the bulk soil when lime was applied, but the response to P addition alone was smaller. These findings indicate that lime and P amendment to soils rich in Al-OM complexes cause destabilisation of OM, but through different mechanisms. Phosphate was found to mainly impact Al³⁺-OM complexes (partly present in the removed free particulate OM) by outcompeting organic ligands for Al³⁺, whereas alkalisation was able to disrupt both the Al³⁺-OM and allophane-OM complexes, and the stability of aggregates. These could be hastened by combined lime and P addition, as made evident by the larger impact of combined lime and P amendments than that of either P or lime addition alone (Chapter 3). After confirming the occurrence of OM destabilisation in the Andosol upon lime and/or P application, we hypothesised that the response of OM preservation (OM stabilisation and mineralisation) to these amendments varies with soil depth. We conducted a 6-month incubation experiment to have an in-depth understanding of the influence of these amendments on OM preservation in soil at different depths. A topsoil (rich in Al³⁺-OM complexes) and a subsoil (with a greater abundance of allophane) of an alu-andic Andosol was incubated with/without inorganic amendments (either lime, phosphate or lime+phosphate) in the presence or absence of an organic amendment (¹³C- and ¹⁵N- labelled barley, Hordeum vulgare L.). By conventional chemical analyses of the bulk soil, we showed an increase in WEOM in both topsoil and subsoil samples that received amendments, particularly of lime (with/without P). However, through a nano-scale secondary ion mass spectrometry analysis of OM-mineral associations in soil microaggregates, we noted that lime amendments decreased OM coverage (particularly plant-derived OM) on the mineral surface in topsoil, but increased it in subsoil (with enhanced coverage of plant-derived OM). These suggested that at these two soil depths with different biogeochemistry, lime addition resulted in OM destabilisation through different mechanisms associated with (i) the displacement of OM from inorganic surfaces in microaggregates in the topsoil, and (ii) the release of OM previously protected within macroaggregates in the subsoil. The total cumulative carbon dioxide (CO₂) emissions and stable C isotopic signature (δ¹³C) of CO₂ showed that lime amendments caused an increase in OM decomposition in the subsoil from both inherited OM (priming) and OM newly formed from barley litter decomposition, but not in topsoil. The increase in OM mineralisation observed in the subsoil (a harsher environment for microbes, with limited bioavailable OM) is consistent with the fact that more favourable conditions were generated by the lime and P addition, which caused an increase in WEOM (Chapter 4). To further understand the distinct responses in OM mineralisation with depth to lime and/or P amendments, we investigated soil bacterial and fungal community composition and their functional profile through high-throughput sequencing analysis. A shift in bacterial and fungal community composition and their functional composition was found in the limed topsoil but not in the limed subsoil. Through structural equation modelling analysis, it was found that in the topsoil, microbial properties, particularly the fungal community composition and functional profile, had a significant relationship with OM mineralisation (with a relatively greater positive or negative coefficient value than other factors). However, in the subsoil, OM mineralisation was only significantly correlated with labile OM in the subsoil. These findings suggested that in the Andosol, the key regulator controlling the response of OM mineralisation to lime and/or phosphate addition shifted with depth from microbial composition and functionality to bioavailable C substrate (Chapter 5). All the results obtained in this thesis contribute to providing a mechanistic understanding of the effect of lime and/or P amendments on OM stabilisation and mineralisation, and have implications for designing climate-smart agricultural management practices of soils with abundant Al-OM complexes.Item The development and assessment of alternative techniques to improve the agronomic value of Dorowa phosphate rock (Zimbabwe) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, School of Agriculture and Environment, College of Sciences, Massey University Palmerston North, New Zealand(Massey University, 2021) Tumbure, AkinsonAgronomically effective P fertilisers are unavailable to most smallholder farmers in Zimbabwe due to the high costs of manufacture and transportation. While phosphorus (P) deficiency remains widespread in these smallholder farming areas, farmers have limited options to ameliorate their soils leading to recurring food insecurity problems. The aim of this thesis was to develop alternative P sources with good agronomic value using locally available materials and alternative techniques such as thermal alteration, co-pyrolysis, and acid leaching. In-order to design alternative techniques, chemical and physical characterisation of the local Dorowa phosphate rock (DPR) was conducted. The DPR contained 89% and 3.5% apatite (hydroxy-fluorapatite) and calcite (CaCO₃) respectively and had a total P (TP) content of 16.5%. With less than 13.5% of TP soluble in 2% citric acid, DPR has limited agronomic value as a direct application phosphate rock. The cadmium (Cd) and fluoride (F) content in DPR was low at 0.16 mg kg⁻¹ and 2% respectively, indicating reduced F and Cd soil contamination issues in final fertiliser products. The DPR generally contained about half the amount of Fe, Al, Mg and K that is reported in literature and this was because the current sample contained less gangue materials. When compared to previous reports on DPR, the observed differences in the current sample were likely as a result of improvements in the mining and beneficiation process, or the current grade of the ore had a higher apatite content. To improve the agronomic value of DPR, the effect of thermal alteration of DPR in the presence of silicate materials (dunite, serpentine and recycled glass) was investigated. Sintering (heating at sub fusion temperatures) was chosen as a less energy intensive process compared to fusion. The sintered DPR mixtures (50% initial DPR content) had an increase of citric soluble P of up to 45, 53, and 73% when mixed with dunite, serpentine and recycled glass, respectively, compared to the unamended DPR. Increases in citric soluble P suggested isomorphous substitution of PO₄³⁻ in fluoro-hydroxyapatite by SiO₄⁴⁻ and or Mg²⁺/Na⁺ for Ca²⁺ and Fe²⁺. The sintered products that had high citric soluble P indicated that they might have improved agronomic value and were recommended for further testing in a glasshouse. Another technique where the DPR was added to maize stover residues (stems + leaves) and pyrolysed at 450 oC was developed and assessed for potential to improve the agronomic value of DPR. A suite of biochar-based fertilisers (BBFs) were obtained from pyrolysis of DPR + maize residues mixed at w/w ratios of 1:2, 1:4, 1:6, and 1:8 (DPR/ maize residues). Except for the 1:2 mixture, co-pyrolysis DPR with maize stover resulted in increases in biochar yield, carbon retention and nitrogen retention of at least 26, 43, and 26% respectively, compared to the pyrolysis of maize stover alone. The 1:6 and 1:8 mixtures produced biochar with more than a 30% increase in citric soluble P compared to the unamended DPR. The results showed that there was potential for on-farm co-pyrolysis of crop wastes with DPR to produce a P source with greater agronomic value. From these results, the 1:6 mixture that had 5.6% total P and 33.6% of the total P citric soluble, was recommended for testing in the glasshouse. The potential of using pyrolysis condensate as a cheaper acid source to recover P from DPR using sequential extractions was also evaluated. Before pyrolysis condensate could be used there was need to ascertain how much P could be recovered from DPR by the common organic acids; citric, acetic, and oxalic acids at various pH values, and then sequentially leached. Results showed that a suspension pH of 3 was necessary for maximum P recovery with citric and oxalic acids solubilising about 21.9 and 46.3% of the total P in DPR respectively, after 3 extractions. The greater P recovery under oxalic acid was attributed to the acid’s ability to remove Ca from solution as evidenced by the Ca:P molar ratio in oxalic acid leachates, which was at least 3 times less than that of other acids tested. Given this potential, a mixture of organic acids in pyrolysis condensate produced from maize stover were evaluated for their P recovery ability. Despite the high acidity and a pH of 3 maintained in leachates, sequential leaching extractions with the aqueous phase pyrolysis liquid over 26 hours was relatively ineffective, solubilising less than 14% of the total P in DPR. Four of the alternative P sources that were developed exhibited high potential agronomic value and were further evaluated for agronomic effectiveness in the glasshouse using broccoli and ryegrass as test crops. After 6 harvests, ryegrass that had been fertilised with DPR: biochar (1:6) or sintered DPR + recycled glass (50%), had similar P uptake and produced at least 95% of the biomass produced when monocalcium phosphate (MCP) was applied at the same citric soluble P rate. The same alternative P sources produced broccoli biomass yields and P uptake that was either comparable to or higher than when MCP was applied. The DPR co-pyrolysis biochar and recycled glass (50%) sintered P sources would provide a good option for smallholder farmers around the Dorowa area in Zimbabwe where PR is mined. However, larger scale field studies are recommended.Item Laboratory study of the behaviour of added phosphate in an allophanic soil : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Soil Science at Massey University, New Zealand(Massey University, 1965) Turner, Max AnthonyA feature in the maintenance of high producing pastures, on the yellow-brown loam soils in Taranaki, is the need for high annual rates of phosphatic fertilizer application. Burgess and Davies (1951) in some early investigations into soil fertility problems in Taranaki noted that the yellow-brown loams could apparently accumulate large amounts of phosphate in a form which was difficult for plants to extract. Consequently to ensure adequate plant phosphate nutrition large annual dressings of superphosphate are recommended for high producing pastures on these soils. This high phosphate-retaining property has been attributed to the presence of active aluminium supplied by allophane, the predominant clay mineral in these soils (Saunders 1959 (b)). The only recent intensive study to be made on phosphate relationships in the yellow-brown loams is that of Saunders (1959 (a)(b)(c)) who carried out chemical fractionation of the phosphate in New Plymouth black loam, a soil which may be considered as representative of the group as a whole. His sampling sites were on areas of different topdressing histories, and although he was able to draw certain conclusions in respect of the trends of phosphate fixation this approach does not provide any information on the shorter term fate of applied phosphate. Information of this kind is, however essential if a rational explanation of the established need for substantial annual additions of phosphate to these soils, is to be forthcoming. [From Introduction]Item Impact of phosphate fertiliser derived fluorine on soil microbiology and white clover (Trifolium repens L) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Environmental Sciences at Massey University, Palmerston North, New Zealand(Massey University, 2019) Thangavelautham, GeretharanFluorine (F) is a significant contaminant in most phosphate fertilisers and fertiliser-derived F is accumulating in New Zealand agricultural soils as a consequent of phosphate fertiliser application. There is potential for soil fluoride (F⁻) to detrimentally affect soil biological functions such as nitrogen fixation by Rhizobium leguminosarum, and to alter soil properties. Fluorine accumulation in soil may require changes to future land use and management practices. The aim of this thesis is to investigate whether phosphate fertiliser-derived soil F has a detrimental effect on soil microorganisms. A novel analytical method for soil F analysis was developed to measure the total soil F concentration based on extraction with dilute NaOH. The relative error between a novel 4 mol L⁻¹ NaOH extraction and the conventional fusion method was < 2 for organic-matter and volcanic parent material derived soils but was > 2 for recent and pallic soils. Precision of the 4 mol L⁻¹ NaOH extraction method, measured through repeat analysis of three further soils (n = 270), was calculated as < 9% Relative Standard Deviation (RSD). To define a standard method to quantify the bioavailable F concentration in soil, samples were extracted with water, 1 mol L⁻¹ HCl, 0.01 mol L⁻¹ CaCl2, 0.01 mol L⁻¹ KCl, and 1 mol L⁻¹ NH4Cl. Compared to water, 0.01 mol L⁻¹ CaCl2 had high relative recovery (of bioavailable F) in soils which have elevated Fe and Al content. Therefore, 0.01 mol L⁻¹ CaCl2 is recommended to measure the bioavailable F concentration of New Zealand pastoral soils. There is no data available which describes the toxic effect of bioavailable F on R. leguminosarum in New Zealand soils. A laboratory incubation experiment and MicroResp 96-well format respiration-inhibition assay were conducted to investigate the effect of F on R. leguminosarum and white clover. Rhizobium leguminosarum growth was not significantly suppressed by F⁻ concentrations less than 100 mg L⁻¹. The normal rod-shaped bacterium cell of R. leguminosarum was morphologically altered when exposed to F⁻ concentrations above 100 mg L⁻¹. The IC10 values determined for F⁻ toxicity to R. leguminosarum were higher than 100 mg F⁻ L⁻¹. Pottle-based experiments showed that white clover growth was not significantly supressed at a F⁻ concentration < 70 mg L⁻¹, while healthy nodules were formed up to a F⁻ concentration of 100 mg L⁻¹. Light and TEM micrographs of nodules revealed that the Rhizobium-white clover interaction was not influenced by F⁻ concentrations up to 100 mg L⁻¹. To assess the potential effects of lime and compost amendment on the bioavailability of F, laboratory F⁻ adsorption/desorption experiments were conducted. Results revealed that at pH < 6, F⁻ adsorption significantly (p < 0.05) increased as a function of compost application. At soil pH > 6, F⁻ adsorption was not significantly (p > 0.05) influenced by compost. Lime application increased the soil pH and maximum F⁻ adsorption was recorded at soil pH between 5.5 – 6.8. These results showed that soil pH significantly influences (p < 0.05) F⁻ desorption and this should be considered in the management of pastoral soil with elevated F. A pot trial was conducted to quantify the effect of added F (equivalent to 0 - 50 years of F accumulation via the continuous application of phosphate fertiliser) on soil properties, soil microbial activity, white clover growth, and R. leguminosarum in an Allophanic soil. F addition (0 – 385 mg kg⁻¹) significantly (p < 0.05) increased soil pH and Dissolved Organic Carbon (DOC) from 5.18 to 5.53 and from 270.5 to 331.3 mg kg⁻¹, respectively. The CaCl2-extractable F concentration increased from 4.95 to 12.67 units as a function of added F. Microbial biomass carbon and soil enzyme activities, and white clover growth and interaction with R. leguminosarum, were not influenced by added F⁻ up to the highest concentration used in this study. White clover variety Merlyn and Tribute shoot F concentration was increased from 4.9 to 19.9 mg kg⁻¹ DM and 5.12 to 16.68 mg kg⁻¹ DM, respectively, however these concentrations are not expected to represent a risk to grazing livestock. This study highlights that the 4 mol L⁻¹ NaOH extraction method is a simple and accurate technique to measure the total F concentration for soils which have high Fe, Al and organic matter content. Water extractable and 0.01 mol L⁻¹ CaCl2-extractable F concentration are recommended to measure the bioavailable concentration of F in New Zealand soils. Current New Zealand bioavailable F concentrations are orders of magnitude lower than the F⁻ concentration assessed to be toxic to R. leguminosarum and white clover, and this suggests there is no imminent risk of soil F to R. leguminosarum. Compost is not recommended as an amendment for soils which have a pH above 6.0 to minimize the bioavailable soil F⁻ concentration. Lime application is suitable in such soils to minimize the bioavailable soil F⁻ concentration through altering soil pH. The major fraction of added F is immobilised by Allophanic soil and this effectively reduces the available F concentration to plants and soil microorganisms. Future work is recommended to investigate the uptake mechanism of bioavailable F into white clover shoots and roots. However, there is no evidence to suggest that F concentrations in New Zealand soil are a risk to New Zealand’s pasture-based farming systems.Item An investigation of the agronomic value of fine grinding and granulating reactive phosphate rocks : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science in soil science at Massey University, New Zealand(Massey University, 1990) Officer, Sally JaneThe future trends in the use of reactive phosphate rocks in New Zealand may be dependent on improving the handling characteristics of these fine sand- and powder-like materials. Granulation of these materials has been suggested as one option. The effect of fine grinding and granulating reactive phosphate rocks on their agronomic performance was evaluated using a range of phosphate rocks, in laboratory studies and in field and glasshouse trials. North Carolina, Arad, Sechura and White Youssafia phosphate rocks, in forms normally imported into New Zealand (sand sized material, majority <2mm particle size), were characterised in terms of origin, composition, particle size, and solubility in 2% formic acid. In a 30 minute formic acid extraction of the imported material, White Youssafia phosphate rock at 44% solubility was found to be less reactive than the other phosphate rocks, which ranged from 47% to 55% in formic solubility In preliminary field trials a very finely ground North Carolina phosphate rock (100% <42µm particle size) was granulated with K2S04. The ungranulated phosphate rock, and granules of 0.5-1mm, 1-2mm and 2-4mm diameter, were evaluated on permanent pasture on the Tokomaru silt loam, using an inverse isotopic dilution technique in which the field soil, at the 1.5-6cm depth, was uniformly labelled with by a novel injection method. No plant yield response to fertiliser was observed but significant differences in herbage phosphate content and specific activity indicated a phosphate uptake response to fertiliser. Despite careful selection of areas of sward which had a similar plant content and vigour, the large variability in data from replicate treatments limited the amount of information which could be drawn from the results but the data indicated that the agronomic performance of the finely ground North Carolina phosphate rock was not limited by granulating to 0.5-1mm (mini-granules). A further range of granulation agents, including neutral salts, iii organic and mineral acids, their salts, and tallow, were tested for their ability to form strong mini-granules from unground North Carolina phosphate rock. The best granulation agent was a 1 :0.6 mixture of citric acid and magnesium sulphate, producing 0.5-1mm mini-granules which had an arbitrary crushing strength of 0.Skg/granule. The production of mini-granules involved pre-drying a phosphate rock/granulation agent slurry until it was just unsaturated, followed by cutting the wet mix through a 0.710mm seive, granulation at high speed for 30 seconds, and drying of the granules at 80°C for approximately 2 hours. This granulation process was then used to manufacture granules from unground Sechura and Arad phosphate rocks, as well as ground North Carolina and Arad phosphate rocks. Ground North Carolina phosphate rock was also granulated using tallow, by melting the fat and mixing in the phosphate rock, followed by setting the mix in a mould. Granulated materials, including a commercially prepared product ("Hyphos"), and ungranulated phosphate rocks (including White Youssafia), were evaluated in a glasshouse pot trial. The fertiliser was applied to the surface of pots of established "Nui" perennial ryegrass, with 7 harvests over three and half months. In general, at the common application rate of 60kgP/ha, the phosphate rock materials were never more than 70% as effective as mono calcium phosphate. The yeilds derived from unground, ungranlated Sechura, North Carolina, Arad and White Youssafia phosphate rocks were similar, the only significant difference being that the yield derived from Sechura phosphate rock·was greater than the yield derived from North Carolina phosphate rock. The effect of mini-granulation on agronomic performance varied with with the type and particle size of the phosphate rock used to make the granules. For example, mini-granulation of "as received" North Carolina and Sechura phosphate rocks caused no reduction in phosphate availability from these materials, however, mini-granulated "as received" and works ground Arad phosphate rock caused a significant reduction in phosphate availability. The agronomic performance of North Carolina phosphate rock was improved by grinding to less than 250µm in particle size but no further improvement occurred if the phosphate rock was more finely ground (<42µm particle size). The agronomic performance of Arad phosphate rock was not improved by grinding. The sequential fractionation of soil phosphate (1MNaOH followed by 1MHC1) indicated that only approximately 8% of the works ground North Carolina phosphate rock fertiliser had dissolved in the soil at the 5th harvest (10 weeks). A comparison of yields derived from pots fertilised with different rates of K2HPO4 sprayed onto chromite (whch had a similar particle size distribution to the unground phosphate rocks) indicated that the dissolved phosphate in the soil from the phosphate rock had a similar agronomic value to the K2 P04 . The low amount of phosphate rock dissolution and the absence of increased of yield response when works ground North Carolina phosphate rock was applied to soil at rates greater than 40 kgP/ha indicated that soil factors were limiting the dissolution of phosphate rock in this experiment. The extent of the limitation varied depending on the phosphate rock type and also the type of pot used (the black polythene bag used for the majority of treatments was enclosed in a galvanised steel cylindar for an inverse isotopic dilution experiment). The variable effects of grinding and granulation were attributed to the limitation of the phosphate rock dissolution. The type of granulation agent (including partial acidulation) had no significant effect on the agronomic performance of the granulated materials, except when tallow was used as a granulation agent and reduced the availability of works ground North Carolina phosphate rock. Unground White Youssafia phosphate rock requires further testing under more rigorous conditions before conclusions can be made about its agronomic availability. Two isotopic techniques were utilised in the glasshouse experiment in an attempt to quantify the extent of phosphate rock dissolution in the soil. The surfaces of some phosphate rock treatments were sprayed with a carrier free solution of P3 2 , and the inverse isotopic dilution technique used in the field was used again on some treatments. The use of labelled K2 H P 3 2 0 4 as a control for the surface labelled experiment provided sufficient information to allow differentiation of phosphate in the plant which was derived from soil and the fertiliser but the model developed could not be directly applied to results from the phosphate rock treatments. The dissolution of different forms of phosphate rock could not be compared using this labelling technique. The inverse isotopic dilution technique was re-evaluated in the glasshouse trial, by uniformly injecting the pots of ryegrass with a carrier free P 2 solution. The fertiliser treatments unpredictably stimulated uptake of labelled soil phosphate, so that the changes in herbage specific activity provided little meaningful information. These two unsuccessful attempts to derive quantitative information from the introduction of the P3 2 isotope into the phosphate rock soil-plant system demonstrated the difficulties involved in using isotopic dilution techniques to examine phosphate rock dissolution in field soils.Item The fate of applied phosphate in a New Zealand yellow-grey earth, as influenced by phosphate carrier and soil reaction : thesis presented as part fulfilment of the requirements for the degree of M. Ag. Sc., Massey Agricultural College, University of New Zealand, Palmerston North, January 1961(Massey University, 1961) Toxopeus, M. R. J.A considerable amount of evidence has been accumulated in support of the presence in soils of iron, alurninium, and calcium bound phosphorus, as products of the phosphorus fixation process, but the quantitative evaluation of these forms has been continuously hampered by the lack of suitable procedures for their separate and selective determination. Although the separate determination of calcium bound phosphorus has been successl (Fraps, 1906; Fisher and Thomas, 1935; Ghani, 1943a) a procedure for the separate determination of iron and aluminium bound phosphorus was not available until recently when Chang and Jackson (1957) included such a method in their proposed scheme for the fractionation of soil phosphorus.Theirs is a definite advance on previous procedures as it has been generally considered that, at least in acid soils, these two forms represent the dominant products of phosphorus fixation, while their relative abundance may be expected to vary considerably in different soils and under different soil conditions. Fife (1959-I, 1959-II) modified the procedure of Chang and Jackson for the separate estimation of Al-P, and (priv.comm.) developed procedures for the selective determination of iron, calcium, and organic P. The object of the present study was to investigate what information these methods could provide concerning the trends of P. fixation in a New Zealand Yellow-Grey Earth from a long term field experiment, embodying three forms of phosphate fertiliser, applied with or without lime. [From Introduction]Item Management aspects of phosphate fertiliser use on hill country : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Farm Management at Massey University(Massey University, 1983) Stewart, Kenneth MFarmer decisions relating to phosphate fertiliser use greatly influence farm profitability, and Farm Advisory Officers receive many requests for assistance in making fertiliser decisions. The Cornforth/Sinclair Phosphate Maintenance Model predicts the annual loss of phosphate from grazed pasture production systems. This model is studied in this thesis and used as the basis for an investigation of phosphate use strategies on a sample of Manawatu hill country properties. Alternative management strategies on three case study farms are analysed.Item Factors affecting phosphate concentrations in surface and subsurface runoff from steep East Coast hill country : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Applied Science, Department of Soil Science, Massey University(Massey University, 1998) Blennerhassett, Jamie DEutrophication is a problem receiving much attention within New Zealand and throughout the rest of the world. Problems associated with eutrophication cause major financial, aesthetic and recreational costs to not only commercial and recreational water users but to society in general. The major nutrient of concern in relation to eutrophication is phosphorus (P) as it is often considered to be the limiting factor. The two major areas from which P enters waterways are point sources and non-point sources. Point sources are relatively easy to identify and quantify. Non-point sources however, are less easy to quantify due to the size of areas from which P is sourced and the number of varying factors which can affect the amount of P which is lost to water-ways. This study investigated P concentrations in surface runoff and subsurface flow from steep east coast hill country. Factors studied included aspect, soil P status, season and fertiliser addition. The study was carried out on grazed pasture farmlets, in which there were 'High P' and 'Low P' fertiliser regimes. Each regime had north and south facing aspects. Four sites were used in the study. High P North (HPN), High P South (HPS), Low P North (LPN) and Low P South (LPS). Simulated rainfall was applied to the sites and surface runoff samples were collected and analysed for dissolved reactive phosphate concentration (DRP). Superphosphate fertiliser was then applied at 20 kg P ha-1 to each site and the runoff procedure was repeated 7 weeks and 14 weeks the lower P soil test values on the south-facing slopes. A water extractable P test provided a better correlation with runoff DRP concentrations for individual runoff events than the Olsen P test. Both tests however, provided poor correlations when all of the Runs were combined. This was due largely to the large increase in DRP concentrations in surface runoff in Run 3 with no corresponding increase in soil tests. There was no apparent relationship between fertiliser regime i.e. soil P status, and the concentration of DRP in subsurface runoff. In Run 3 however, there was a marked increase in subsurface DRP concentration for both sites which was consistent with the surface runoff results and supported the theory of soil moisture playing a major role in determining the DRP concentration in water. The study suggests that the greatest risk of P loss from soil to surface waters will be from northerly aspects with high fertiliser histories during the summer months when soil moisture levels are low.