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    An evaluation of sulphur topdressing strategies in Eastland pastures : a thesis presented in partial fulfilment for the requirements for the degree of Master of Agricultural Science in Soil Science at Massey University
    (Massey University, 1982) Nguyen, Minh-Long
    Two sampling surveys for soil and herbage, one in autumn and the second in the following spring, were carried out to assess the pasture sulphur status in the Eastland area of the North Island. A preliminary glasshouse experiment using ryegrass as an indicator plant was also conducted to determine which soil test method best estimated the plant available sulphur pool in the soils covered by the survey. In comparison with calcium chloride extractable sulphur, soil sulphur extracted with calcium phosphate solution was shown to relate well to the yield response of ryegrass. Thus a calcium phosphate extractant was used as the criterion of soil sulphur status in the survey. In most of the soils surveyed, the levels of phosphate-extractable sulphur tended to decrease with depth down to 30 cm and were not constant throughout the year. Levels were lower in spring than in autumn, possibly due to the leaching loss of sulphate and the slow mineralisation rate of soil organic sulphur during winter. The decrease in soil sulphate levels during winter was observed even at sites with low annual rainfall (900 - 1000 mm) and in soils with anion retention capacities as high as 70% as measured by the phosphate retention test. Although the levels of Olsen extractable soil phosphorus also tended to decrease over winter, this decrease in available phosphorus was not nearly as great as for sulphate, suggesting that sulphate, being the more weakly adsorbed anion, had been leached more readily. Soil sulphur levels in autumn also reflected the sulphur fertiliser history more markedly than those in spring, thus providing further evidence of sulphate leaching during winter. The results obtained from the herbage survey were consistent with those derived from the glasshouse study and soil survey in showing that the sulphur status of pasture herbage, whether expressed in terms of total sulphur, sulphate or N:S ratios was generally lower in spring than in autumn. The lower sulphur status of soil and herbage in spring suggests that if sulphur deficiencies do occur in the Eastland pastures, they may be most apparent in early spring. To confirm the suspected spring sulphur deficiency observed in the survey, five field trials were laid down in the spring of the following year on soils belonging to three New Zealand soil groups: a yellow-grey earth, an intergrade between yellow-grey and yellow-brown earths and a yellow-brown pumice soil. Significant yield responses to spring application of sulphur were recorded at three out of the five sites. These sulphur-responsive sites included both those where there had been no recent application of sulphate-containing fertiliser and also those which had received regular autumn applications of sulphate at rates of 25 to 33 kg S hā¹ annum̄¹. Spring application of sulphur-free nitrogen fertiliser greatly increased dry matter yield but did not appear to aggravate the effect of sulphur deficiency on pasture growth at the sulphur-deficient sites, as evidenced by the fact that yield responses to sulphur application in the presence of nitrogen fertiliser were of similar or lower magnitude than those obtained with sulphur in the absence of nitrogen fertiliser. However, spring application of sulphur-free nitrogen led to very wide N:S ratios (18:1 to 23:1) in mixed herbage at two sulphur-deficient sites. In such situations, there may be a decrease in the nutritive value of the extra feed produced by a tactical application of nitrogen fertiliser.
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    Adsorption of sulphate by soils : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Soil Science at Massey University
    (Massey University, 1983) Marsh, Kenneth Blair
    Studies of sulphate adsorption, phosphate sorption and surface charge on soils of varying anion sorption ability which had been incubated, each with several rates of calcium hydroxide, have indicated that: (i) The amounts of both sulphate and phosphate sorbed from 0.1M NaCl can be correlated with surface positive charge, but whilst there is a 1:1 relationship between the amounts of sulphate adsorbed and surface positive charge phosphate is sorbed in amounts well in excess of the amounts of positive charge present. (ii) Although there is a requirement for some positive charge on the surface before sulphate adsorption can occur in both 0.1M NaCl and 0.025M CaCl2, there is a strong selectivity for sulphate over non-specifically adsorbed ions such as chloride. (iii) Sulphate is adsorbed from 0.025M CaCl2 in excess of the amounts of surface positive charge initially present (y = 1.51x + 1.45), an observation which is consistent with a closer approach of sulphate to the surface in the presence of calcium such that the actual surface charge is modified. These findings point to a predominantly electrostatic link between sulphate and the surface, with the changes in sulphate adsorption with pH being dependent on changes in surface positive charge. Sulphate adsorption was strongly reduced (10 - 60%) by increasing pH, and in a study of competitive sorption was also significantly (10 - 30%) reduced by addition of phosphate. An investigation with one soil showed that the measured charges in sulphate adsorbed on phosphate addition were highly correlated with measured changes in surface positive charge, and there was some evidence for phosphate having a larger effect on surface positive charge at low pH.
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    An investigation of some factors influencing the rate of oxidation of elemental sulphur fertilizers : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1990) Chatupote, Wichien
    Methodologies for measuring the particle size of So in pure and compound fertilizers (sulphurized superphosphates (SSP), reactive phosphate rocks (RPR) and partially acidulated phosphate rock (PAPR)) and for determining the rate at which So in these materials oxidises in soils were evaluated and improved. Sample dispersion in 10% HC1 followed by wet sieving was the most successful method for sizing So in SSP, RPR and PAPR based fertilizers. So/bentonite fertilizers, however, were more easily dispersed in water than in acid. Acetone extraction (40 g:200 ml acetone, using a 16 h shaking period) and determination of So in the extract proved to be a suitable method for measuring amounts of So in finely ground fertilizers and soils at concentrations above 5 μg S g-1 soil and below 200 μg S ml-1 acetone. The rate of So oxidation in soil was determined by regularly measuring residual amounts of So. The influence of soil type and fertilizer history on the potential of soils to oxidise So was examined in incubation studies. On average, soils that had previously received So applications had higher initial rhodanese enzyme activities (RA) and higher So oxidation rates but there was no simple relationship between fertilizer history or RA and initial So oxidation rate. Different sources of So, namely Rotokawa So (geothermal So), dark So, Damman So, and agricultural grade So had similar oxidation rates per unit surface area. Granules or prills oxidised slowly in incubated soil because they did not disintegrate when placed in soil and had small specific surface area. On average, the oxidation rate of So was increased when mixed or granulated with reactive phosphate rocks and incorporated in soil but this effect was not consistently reproducible. Further incubations of So in the presence of various combinations, CaHPO4, CaCl2 and CaCO3, demonstrated that the presence of CaHPO4 and CaCO3 could elevate So oxidation rates. Granulation of RPR and PAPR with So did not significantly increase (p >0.05) the oxidation rate of So surface applied to undisturbed pasture soils (glasshouse and field trials). Under surface application conditions granulated So had similar oxidation rates to finely divided So forms. An iterative computer program was developed to calculate specific oxidation rates (K, μg So cm-2 day-1) from the amounts of acetone extractable So remaining in soils at different times. On average, K for <150 So μm was significantly lower (p <0.05) when surface applied to undisturbed soil cores than when incorporated into incubated soils. Specific oxidation rates of different particle sizes (<150, 150-250 and 250-500 μm) of surface applied So were similar (ranging form 11-19 μg So cm-2 day-1) but were different (P <0.05) for the two soil types used in glasshouse trials (means of 17 and 13 μg So cm-2 day-1 for Ramiha and Tokomaru soil, respectively). Corrections for the effects of soil moisture on oxidation rates provided evidence that all So could have similar maximum potential K values (Kmax = 18 μg S cm-2 day-1) in both soils. This suggested, with other evidence from the literature, that So oxidation in soil could be effectively modelled by knowing So particle size and the effects of soil moisture and temperature on So oxidation. A So oxidation simulation model was constructed using a value for Kmax determined in the glasshouse trials. Within experimental error, the simulation model predicted So oxidation in field soil well (explaining between 76 and 97% of data variance at 3 field sites) and provides a useful basis for designing future research projects.
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    Measurement and modelling of chloride and sulphate leaching from a mole-drained soil : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1991) Heng, Lee Kheng
    A study of the leaching of sulphate, chloride, nitrate and the associated cations was carried out over two winter periods on three mole-drained paddocks on a yellow-grey earth (Tokomaru silt loam). The paddocks were occasionally grazed by sheep. At the beginning of each drainage season potassium chloride (KCl) and sulphur fertilizer, as either single superphosphate (SSP) or elemental sulphur (S°), were applied to two of the paddocks, while the third served as a control. The amount of KCl applied was 200 kg ha-1 yr-1, while sulphur was applied at 50 kg S ha-1 in 1988 and 30 kg S ha-1 1989. Drain flow from the fertilized paddocks was measured with V-notch weirs, and sampled using proportional samplers. Large differences in the total drainage flow were measured in the two years, with values of approximately 280 mm in 1988 and 110 mm in 1989. Significant amounts of the chloride added through both fertilizer and rainfall were leached, amounting to approximately 105 kg Cl ha-1 yr-1. The leaching of sulphate-S depended on the form of S fertilizer applied, the quantity of drainage, and the rate of mineralization. Leaching losses of 17 and 3.4 kg S ha-1 were measured from the SSP and S° fertilized paddocks, respectively, in 1988, and 9.4 and 3.5 kg S ha-1 in 1989. The study showed that applying SSP just before the drainage season increased leaching losses of sulphate-S substantially. Although the particle sizes of S° used in both years were much bigger than those specified by the Ministry of Agriculture and Fisheries of New Zealand, there appeared to be no difference in the yield response to S applied either as SSP or as S°. The reduced leaching of S when applied as S° resulted from the slow oxidation of S° to sulphate-S. Relatively little nitrate-N was leached, the amount ranging from 11 to 17 kg N ha-1 yr-1. Losses of potassium were less than 10 kg K ha-1 yr-1, despite the large quantity applied as KCl fertilizer immediately before winter. However a large amount of calcium was leached, between 31 and 52 kg ha-1 yr-1. The amount of magnesium leached was between 9 and 15 kg ha-1 yr-1. A considerable quantity of sodium was leached, around 58 kg ha-1 in 1988, and 31 kg Na ha-1 in 1989, roughly equal to the input in rainfall. Good mass balances were obtained for both chloride and sulphate. The measured moles of negative and positive charge from cations and anions in the leachate were also almost equal. Three models were developed for the leaching of chloride and sulphate-S. An approach dividing the soil water into mobile-immobile phases, and using a fairly detailed soil water flow model was developed. The model was able to simulate the concentration of chloride in the drainage closely, even just after the application of chloride fertilizer, and during highly preferential flow conditions induced by heavy rain. A transfer function model, assuming a log-normal probability density function (pdf) of solute travel pathway lengths, was able to simulate the leaching of chloride reasonably well in 1988. The prediction was less satisfactory in 1989 and during highly preferential flow. By adapting the pdf for chloride to sulphate and by taking adsorption of sulphate into account, the model could predict the sulphate concentration in the drainage quite successfully. A simpler model, using the idea that the two-dimensional flow geometry to the mole drain implies that the drainage concentration approximately equals the average soil solution concentration, was also developed. Despite its simplicity it was able to simulate the leaching of chloride and sulphate as well as the transfer function model. Irrespective of the model being used, the net mineralization rate of soil organic sulphur emerged as an important factor in predicting the leaching of sulphate.