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Item Factors influencing the transformation and fate of sulphur and nitrogen in grazed hill country pastures : 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) Sakadevan, KaruppanThe increasing cost of agricultural grade sulphur and the high leaching losses of sulphate sulphur(S) from superphosphate fertilized pastures in New Zealand create a need to develop more efficient S fertilization techniques. The objective of the present study was to identify the main origins of the sulphate being leached from superphosphate fertilized hill country pastures with soils (Typic Dystrachrepts) developed from underlying sedimentary parent materials. Origins of leached sulphate were categorized as S leached directly from fertilizer, from zones enriched in animal excreta and from the mineralization of soil organic matter. Mineralization studies, both in la??oratory and in field were conducted to establish the extent of and the relationship between sulphur and nitrogen mineralization and the fate of mineralized nutrients in pasture soils that contrasted in their superphosphate fertilizer history. In the preliminary laboratory study in which an open incubation technique was used to measure potential net mineralization, top soils (0-7.5cm) taken from sites that had received higher rates of superphosphate in the past, mineralized more soil organic sulphur and nitrogen than soils taken from sites that had received smaller amounts of superphosphate in the past. In addition top soils collected from low slope (0-12°) sites where a greater proportion of animal excreta is returned, mineralized more S and N than the soils from medium slope (13-25°) sites. The ratio of N to S mineralized was narrower (2. 0 to 3. 6 ) than the N to S ratio of the whole soil (7 .1 to 8. 9) suggesting that in these soils relatively more S remains in a mineral form in the soil and is more susceptible to leaching than N which is conserved in the soil. Cylindrical, mini-lysimeters with ion exchange resin traps for collecting solutes from drainage water were developed to measure the net mineralization of soil organic S and N under field conditions. Leaching losses of S and N, pasture uptake of S and N and changes in mineral S and N pools in the soil at the same site were measured simultaneously and the rate of mineralization calculated. A laboratory evaluation of the lysimeter showed that the resin trap was capable of removing all the sulphate from drainage water at several different flow rates. The main advantage of these lysimeters over the conventional methods of measuring the leaching losses of anions and cations in the field is that regular drainage collection was not necessary. By introducing mixtures of both anion and cation exchange resins in the trap in the lysimeter it was possible to monitor the amount of anions and cations in field drainage over long periods of time before it was necessary to change the resin mixtures. In the initial field lysimeter study the net mineralization and pasture uptake of N ( 119 to 251 kg N ha-1) was 10 times more than that of S ( 12 to 27.5 kg S ha-1) , yet approximately 10 times more sulphate S ( 2.0 to 17.3 kg S ha-1) than mineral N (0. 19 to 1.3 kg N ha-1) was lost by leaching. Previous fertilizer history had a marked effect on the leaching losses of sulphate with seven times more S lost ( 2.1 vs 1 5.3 kg S ha-1) from sites which received greater rates of superphosphate and had higher stocking rates. During the initial seven month period S leaching losses on the low and high fertility sites were equivalent to 1 5% and 3 3% of the annual fertilizer application. More sulphate was leached from areas identified as animal camping areas. The lack of any change in sulphate below the 150mm soil depth during a period of active plant growth and no leaching suggested that any sulphate that moved below 1 50mm of the soil could be considered to be effectively lost from the system. Increased leaching losses of calcium and magnesium were associated with increased sulphate losses. The amount of calcium lost by leaching ( 4.7 5 to 12. 5 ,kg Ca ha-1) was far greater than potassium (0.8 to 3 . 6 kg .K ha'1), although twice the amount of potassium ( 240 kg K ha·1 vs 120 kg Ca ha'1) was. cycled through the plant-animal system. The amount of magnesium lost by leaching was greater than the amount of potassium lost by leaching. In a second lysimeter study the direct effects of freshly applied fertilizer on the mineralization of S and N from soil organic matter, their plant availability and losses by leaching were studied under field conditions using 35S labelled superphosphate. Fertilizer application significantly increased the mineralization of both organic S and N. The recovery and measurement of 35S activity over a nine month period showed that major proportions of pasture S ( 8 5 and 8 6% of the pasture S for low and high fertility farmlets, respectively) and leached S (75 and 87% of the leached S for low the mineralization of soil organic matter and not recently applied fertilizer. The amounts of both S and N mineralized from soil organic matter depends upon the past fertilizer history of the site and the present fertilizer application rate (22 and 40 kg S ha-1 and 125 and 204 kg N ha-1 for low and high fertility farmlets, respectively). Further, when the net mineralization of S was greater a greater proportion (59%) of mineralized S was lost by leaching than removed by pasture (39%). Irrespective of the amount N mineralized virtually all was removed by pasture. The results suggested that low N availability was a major factor limiting carbon fixation and the formation of organic S in these pasture soils. In a third lysimeter study, field simulated sheep dung and urine events boosted pasture growth and S and N uptake by approximately (50%), whereas the leaching losses of S and N were not influenced by the their application. A preliminary computer simulation model describing the mineralization of soil organic S, pasture S uptake and leaching losses in grazed pasture was developed. The preliminary model gave reasonable predictions of the changes in soil sulphate concentrations in the soil up to a depth of 25cm, pasture uptake of S and leaching losses of S at four pasture sites varying in their fertilizer history. Further refinement of the model is necessary before it can provide the basis for predicting fertilizer S requirement for hill country pastures. The experimental results and model output confirm balance study predictions that large leaching losses of S occur and these are derived mainly from the mineralization of soil organic matter which accumulates in well fertilized soils. The extent of S losses appear to be a function of the general levels of soil productivity and the data suggested that only a small, probably less than 20% reduction in this loss could be achieved by changing to slow release S fertilizers.Item A comparison of the fate of elemental sulphur and sulphate sulphur based fertilizers in pasture soils : 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) Phimsarn, SathienNitrogen fixation by legumes has a particular requirement for adequate soil sulphur status. Sulphur (S) is a mobile nutrient and is easily leached from aquic soil environments, therefore regular topdressing with S fertilizer is required to maintain legume vigor and pasture production in most New Zealand pasture soils. Escalating fertilizer costs have focused attention on the efficiency of use of S fertilizers, particularly superphosphate (SSP) and alternative elemental S (S0) based fertilizers less liable to leaching loss in this aquic environment. Field and glasshouse trials, using the resident clover/ryegrass sward on undisturbed soil cores (150 mm diameter, 100 mm depth) , were undertaken to determine the comparative short-term fate of SSP and different particle sizes of S0. Methods for manufacturing radioactively labelled (35s) fertilizers were developed. In addition, the effect of sheep dung on the short-term immobilization of soil and fertilizer S was also investigated. A simple computer simulation model explaining the observed transformation of soil sulphur and 35s labelled fertilizer was developed. Initially, the effect of sheep dung on the short-term immobilization of soil and fertilizer S was investigated. Very small amounts (about 2-5%) of plant (clover/ryegrass pasture) S and P, within 1 00 mm of the area surrounding the dung pellet, were derived from the dung. Under the experimental conditions that prevailed, dung S behaved as a slow release S form causing neither greater immobilization of soil or fertilizer S nor mineralization of soil organic S. It was concluded that the impact of dung return on short-term (< one year) S fertilizer fate need not be considered. An initial field trial comparing the fate of microfine S0 (< 0.010 mm) relative to sulphate-based SSP was undertaken on Tokomaru silt loam, a New Zealand yellow-grey earth (Fragiaqualf). The microfine S0 oxidized within 30 days of application but initially (up to 60 days) was slightly less effective than SSP in terms of plant uptake. Over longer periods of time (150 days) their performances were comparable. Final cumulative plant uptake at 150 days accounted for 13.6% of microfine S0 and 16.3% of the SSP-sulphate. The major transformation of 35s from microfine S0 and 35s belied gypsum In SSP to soil organic 35s forms occurred in the first 30 days after application. The organic 35s activity formed from 35s0 was twice that formed from sulphate-based fertilizer and was mainly carbon- bonded 35s in the top 33mm of the pasture soil profile. The amount of organic 35s remaining as carbon-bonded 35s decreased with soil depth and the reverse occurred for the estersulphate 35s. By 1 50 days, greater activity from the microfine 35s0 remained in the soil organics fraction than from the sulphate-35s fertilizer, indicating that more soil organicS reserves may be formed through the use of fine S0 fertilizer than from the sulphate-based fertilizer. This also indicated the advantage of using S0 in minimizing the S leaching losses in this aquic environment. An inverse dilution technique using an isotope injector developed at Massey University to uniformly label undisturbed soil cores with carrier-free 35so4= solution was used to measure the impact of S0 and sulphate-based fertilizers on the fate of soil S. Results were consistent with the labelled fertilizer technique and both techniques indicated rapid incorporation of 35s into soil organic S and that the carbon-bonded S formed was likely to be a subsequent source of mineralized S available to plants. Soil samples from the preliminary field study were used to evaluate soil preparation and extraction techniques. Soil sampling and preparation techniques were evaluated on the basis that an extract sampling the plant available S pool in soil should have the same 35s specific activity as plant growing on that soil. The average 35s specific activity in a calcium dihydrogen phosphate (CaP-S) (0.04 M) extract from a freeze-dried sample of the top 60 mm of a pasture soil was most closely related to the 35s specific activity of plants growing on that soil. CaP-S extracts from field-moist soil or 0.01 M CaCI2 extracts from field-moist or freeze-dried soils had higher specific activities than plants. lt was concluded that plants were able to extract soil S from soils which was not exchangeable with added 35so4= fertilizers during either the field experiment or extraction with 0.01 M CaCI2. The second series of field and glasshouse trials were conducted to investigate the fate of 35s labelled SSP, gypsum and S0 of varying particle sizes (<0 . 1 50 mm, 0.1 50-0.250 m m and 0.250-0.500 mm, in granulated and non-granulated forms) in two pasture soils contrasting in mineralogy and fertility status. Under glasshouse conditions, 50 mm of simulated rainfall was applied to each of the undisturbed soil cores during the first 56 days after fertilizer application. For the remainder of the period, cores were watered from below using a saucer. Field cores remained subject to the local climate. Both the rate of oxidation in soil and the efficiency of plant use of S0 was improved by decreasing its particle size. Relative to soluble so4=-s applied as gypsum or SSP, the plant utilization of oxidized SJ was similar. Granulation of finer S0 with or without finely ground phosphate rock had little effect on the long-term ( 180 days) oxidation rate or the efficiency with which, after oxidation, finely ground S0 was taken up plants. Apart from S0 of large particle size (>0 . 1 50 m m) which had not oxidized, the major fate of fertilizer 35s, either under glasshouse or field conditions, was again in soil organic matter mostly formed in the top 33 mm of the soil. Applications of gypsum and SSP caused 35s to move to the 33-1 00 mm soil depths but there was no additional influence of P on the depth to which so4= was leached. A preliminary computer simulation model describing the fate of 35so4 =-s fertilizer was developed. The model provided a very accurate method of predicting plant uptake of S from both SSP fertilized and u nfertilized soil cores. The model also indicated that, at any particular soil depth, on average, actual rates of mineralizatio n a nd i m mobilization may exceed root uptake of S by 1.5 to 2 fold (mg S turned over per unit of S taken up by plants). The accuracy of the estimated turnover rate could not be validated because the model gave relatively inaccurate predictions of the measured movement and transformations of 35s tracer added to the soil as SSP. There was, however, relative similarity between the observed and predicted proportional distribution of 35s between soil and plant S forms. Such a distribution supported the concept of using root activity as a modifier of mineralization and immobilization rates in order to describe the extent of these processes at different soil depths. The study has emphasized the greater importance of the surface few millimeters of pasture soil in S transformations, important in the fate of fertilizer and pasture plant nutrition. There appears to be scope in manipulating S0 particle size to improve the efficiency of the S fertilizer used.Item 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, WichienMethodologies 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.Item Modelling sulphate dynamics in soils : the effect of ion-pair adsorption : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 2007) Cichota, RogerioSulphur is an important nutrient to plants, and reports of its deficiency have been increasing worldwide. Sulphur starvation causes losses in both yield and quality, and it reduces nitrogen use efficiency of plants. As the timing for fertilisation can be decisive for avoiding deleterious effects, improvements in the description of the sulphur balance in fields are a valuable contribution for assisting fertiliser management. Sulphate is the most important inorganic form of sulphur in soils. Being the mobile form, sulphate is readily available for plants, and also prone to be leached. Therefore the description of the movement of sulphate is the key component of the sulphur balance. Leaching of sulphate from the soil can be significantly delayed by its adsorption onto the soil particles. Soil type and pH are the main factors defining the sulphate adsorption capacity; although the presence of other ions in the soil solution can have a considerable effect. It has been reported that in some soils, typically volcanic and tropical soils with variable-charge characteristics, the co-presence of sulphate and calcium can substantially enhance their retention via ion-pair adsorption (IPA). To determine the influence of cations on the movement of sulphate, series of batch and miscible displacement experiments were conducted using two New Zealand soils, of contrasting ion adsorption capacities: the Taupo sandy and Egmont loam soils. These experiments demonstrated the occurrence of cooperative adsorption of sulphate and calcium in the Egmont soil, but not in the Taupo soil. Batch experiments were conducted to examine the IPA adsorption process in the Egmont soil in more detail. Based on the analyses of the results from these two series of experiments, plus the review of published data, three different mathematical approaches for evaluating the amount of solute adsorbed as ion-pairs are proposed. A computer program was built for solving an adsorption model using these three approaches, and was used to compare the model's predictions and the observed adsorption data. An extension of this program, coupling the adsorption model with a solute transport description, was used to simulate the movement of sulphate and calcium. Comparisons between the data from the miscible displacements and the results from this model are used to demonstrate the applicability of the proposed IPA description for modelling the transport of these ions in the soil. Finally, results from a pot trial with Egmont soil are used to examine the relevance of IPA for the movement of sulphate under non-equilibrium conditions, and with active plant growth. Although the results from this experiment regarding IPA were statistically non-significant, some insights could be obtained and are discussed. More studies involving IPA under non-equilibrium experiments are needed for a better understanding of the relevance of IPA in field conditions.