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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 Potassium releasing and supplying power of selected yellow grey earth soils of New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1994) Surapaneni, AravindThe supply of soil potassium (K) to New Zealand pastures is currently being assessed by the quick test K (QTK) and reserve K (Kc) methods, which measure soil exchangeable K (Kex) and non-exchangeable K (Knex), respectively. QTK is based on a routine soil test and Kc is an assigned estimate appropriate to the soil group. No consideration is given to the variations of the Knex supply within a soil group. The objective of this research was to examine the K releasing and K supplying power of selected soils from the yellow-grey earth (YGE) group. A wide variation was observed in the measured Kc values of the YGE soils in the North and South Islands. A glasshouse experiment showed that the supply of Knex to ryegrass grown on the 13 North Island YGE soils ranged from 0-41 mg 100 g-1 and that of the 6 South Island YGE soils ranged from 3-35 mg 100 g-1. The experiment also showed that there were lower levels of Knex supply in the pasture sites, compared to the virgin sites with respect to the South Island YGE soils. These results have implications to the use of the soil group concept which is used to estimate Knex supply in the Computerised Fertilizer Advisory Service (CFAS) K model, currently used by AgResearch. In a laboratory study, the threshold K levels in terms of K concentration and the activity ratio in the equilibrated soil solution, Kex, and the amount of specifically held K were determined, in order to explain the variations in Knex, supply. The threshold K levels were not related to the Knex release and supply. The uptake of K by ryegrass was at best poorly to moderately correlated with the K extracted by current methods of determining K releasing power viz, QTK and Kc. The highest simple correlation was obtained from an improved acid-extractable K procedure (r = 0.96; P < 0.01). The differences in the Knex uptake by ryegrass from various soils were better explained by a simple method of determining soil Knex i.e., step K, than by the existing Kc method. A multiple regression equation with QTK and step K as independent variables explained 96 % of the variation in total K uptake among soils. On the basis of Knex taken up by ryegrass in the glasshouse experiment, the 19 soils in this study were broadly grouped into two categories (i) soils with step K values of less than 35 mg 100 g-1 and a Kc range of 8-10 mg 100 g-1 and (ii) soils with step K values greater than 35 mg 100 g-1 and a Kc range of 12-19 mg 100 g-1. Selected soils were fractioned into sand, silt, and clay separates and acid-extractable K levels of the fractions were measured. There was a wide range in the acid-extractable K levels among the soils for the same size fraction e.g., clay, and for different size fractions within the same soil. When weighted according to the particle size distribution of the soil, the sand was found to contribute 4-45 %, silt 10-40 %, and clay 15-85 % of the K released by the sum of the 3 separates, using the improved acid extraction method. In all the soils, the clay separate released the most K per unit weight. An agar pot trial technique was developed to measure the K supplying power of the soil separates. Although on a unit weight basis the clay separates showed a much greater activity than the other separates on a weighted basis, the contributions of sand and silt separates to the total K uptake of Marton (38 %), Matapiro (41 %), and Wharekaka (25 %) soils was of considerable importance. The results demonstrated that the role of sand and silt separates deserve more consideration in estimating potential K releasing and supplying power than has hitherto been the case. The study also attempted to relate Knex release and supply to the soil mineralogy. Although the gross mineralogy of the 19 soils was similar, differences in the Knex release and supply could be related to subtle differences and gradual changes in the clay mineralogy. The XRD patterns of the clays with a Kc range of 8-10 mg 100 g-1 of soil differed from those with a Kc range of 12-19 mg 100 g-1 of soil. The latter group of clays contain more K bearing minerals than the former group. The practical implications of the measured differences in Kc values (Knex supply) within the YGE soil group were dealt with. The measured Knex supply in the North Island YGE soils ranged from 20-40 kg ha-1 yr-1, whereas the expected Knex supply based on an assigned Kc value is 30 kg ha-1 yr-1. The difference between the expected and the measured Knex may be sufficiently economically significant as to invalidate applying a single Kc value to a soil group. Possible improvements to the soil K supply component of the CFAS K model were suggested, particularly that step K values should replace Kc in the K supply model.Item The phytoextraction of heavy metals from metalliferous soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University(Massey University, 1997) Robinson, Brett Harvey; Robinson, Brett HarveyThis study concerns the investigation of the potential use of plants to remove heavy metals, in particular nickel, zinc and cadmium, from soils. The study is divided into three sections, bioavailability, phytomining, and phytoremediation. The effect of various extractants on the solubility of heavy metals in some soils was tested. It was found that the solubility of the metal invariably increased as the pH of the extractant decreased, and as the concentration of the extractant increased. These relationships could be predicted mathematically. It concluded that a more concentrated, neutral, non-chelating extractant such as 1M ammonium acetate, is the most suitable for estimating bioavailability. An investigation into the addition of some compounds to soils to increase metal solubility showed that EDTA and citric acid should maximise solubility while keeping soil parameters (pH, osmotic potential, nutrient availability) within the growth range of the plant. These compounds are also relatively inexpensive. The effect of bioavailable elements on a New Zealand serpentine flora was investigated with regard to the soil's potential for phytoextraction. It was found that nickel was the only element that would be suitable for phytoextraction from these soils. The relative infertility of the serpentines was attributed primarily to the toxic effects of magnesium and/or nickel. Removing nickel from the soil by phytoextraction may enable the soil to be used as a magnesium-rich fertiliser. The potential of the hyperaccumulator plants Alyssum bertolonii and Berkheya coddii for nickel phytoextraction was studied. With the addition of fertilisers, the plants could remove respectively in excess of 72 kg and 100 kg of nickel per hectare per annum. Were the metal to be sold, and energy from the plant's incineration utilised, the net profit per hectare would be greater than that of a crop of wheat. Both of these plants re-grew after harvesting without the need to re-sow. In the case of B. coddii, the nickel concentration in the regrowth was more than twice that of the original crop. Phytomining for nickel is a viable proposition provided the operation is carried out over a large area. The nickel concentration in the plants was logarithmically related to the nickel extracted by a 1M ammonium acetate extract. Theoretical nickel yields from various soils could be predicted by performing a 1M ammonium acetate extraction on the soils. About half of the soils tested from various locations around the world contained enough soluble nickel to be economically phytomined. Alyssum bertolonii and B. coddii also have the potential to remove nickel from polluted soils. The addition of EDTA and citric acid to the soil in which the plants grew actually decreased the nickel concentration in the plants despite increasing the nickel solubility in the soil. The economics of phytomining are closely linked to the value of the metal. Cobalt and possibly even the noble metals could be economically phytomined at low concentrations in plants: a fertile area for future research. Sequential extractions were used to model the effect of successive hyperaccumulator crops on the bioavailability of nickel in ultramafic soils from around the world. The nickel concentration in all of the soils tested, decreased in a regular manner and could be predicted mathematically. Assuming an initial nickel crop of 100 kg/ha, the number of nickel crops above 70 kg/ha that could be obtained was calculated for each soil. The number of economic nickel crops varied between 3 and 18 before the soil would have to have been modified to increase nickel bioavailability. The possibility of removing zinc and cadmium using Thlaspi caerulescens showed that the plant has a potential use for removing cadmium from weakly polluted soils. The low bioaccumulation factor for zinc accumulation means that this element will never be removed in a reasonable time span. The concentration of both zinc and cadmium in the plant could be predicted by the extractable fraction in the soil as estimated by using 1M ammonium acetate as extractant. It was concluded that phytomining and phytoremediation are feasible possibilities under certain conditions. (1) Metals necessarily have to be slightly soluble in the soil before they can be phytoextractcd. Metal solubility may be improved by the addition of chemicals such as chelating agents. (2) Due to relatively low yields, phytomining will only be viable for more valuable elements where the concentrations in soils are too low for conventional mining. (3) Phytoremediation will be most effective on weakly polluted soils. (4) The economics of phytoextraction favour its use over large areas. The amount of metal able to be extracted from an area can be predicted by performing an extraction with 1M ammonium acetate.Item Characterisation and amelioration of low pH conditions in pyritic mine pitwall materials, Martha Mine, Waihi, New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University(Massey University, 1998) Gurung, Shivaraj; Gurung, ShivarajThe objective of this thesis was to research the processes associated with the generation of low pH conditions in pitwall rock material at Martha Mine, Waihi, and evaluate the ameliorating effectiveness of some selected acid neutralising materials with an aim to create suitable plant growth media. Approximately 25% of the current pitwall area is affected by pyrite oxidation, resulting in the formation of acid mine drainage (AMD) which limits long-term establishment of vegetation. The results of this study showed that slope gradient, variable cover material distribution and persistent rill and sheet erosion on the pitwall are some of the physical characteristics restricting plant establishment. Weathered cover materials varied in depth from 5 mm on the upper slopes to > 300 mm in the lower colluvial section of the pitwall. The uneven distribution of pyrite mineralisation has resulted in microenvironments of "acid pockets" in oxidised parts of the pitwall. The fresh pyritic rock had a near neutral pH while the strongly weathered materials generally had pH < 3.0. Based on the total sulphide S content (2.51%). the fresh rock had a net acid producing potential (NAPP) of 51 kg CaCO3 t-1. Weathered material still contained significant amounts of sulphide S but because of negative neutralisation potential (NP), it had a higher NAPP of 82 kg CaCO3 t-1. Kinetic net acid generation (NAG) test revealed that the fresh rock, when exposed, had a lag-period of 22 weeks for the onset of biochemical oxidation. However, the degree of pyrite liberation from the host rock materials is likely to effect the lag-period. The effect of progressive weathering and oxidation was to cause major losses in base cations except for K, which showed an anomalous enrichment, due to incorporation into clays and jarosite-type minerals. Weathering also caused relative enrichment in Ba and As contents of the pitwall materials. Run-off water collected from the bottom of the pitwall had the characteristic AMD composition of low pH and high dissolved metal concentrations. The spatial variation of pH of the weathered pitwall rock in the study area was in the range 2.0-4.6 while EC varied from 1.9 to 4.3 dS m-1. The study area generally contained high concentrations of soluble Fe (2506-5758 mg kg-1), Mn (203-635 mg kg-1), exchangeable-Al (4.8-10.8 cmolc kg-1), SO4 2- (1650-3400 mg kg-1) and acidity (121-668 kg CaCO3 t-1). Overall, NAPP distribution varied from 35 to 143 kg CaCO3 t-1. A buffer curve lime requirement (LRBuffer) to raise the pH of the weathered pitwall rock material to 6 (29 kg CaCO3 t-1) amounted only to 35% of the acid base accounting (ABA) value of 82 kg CaCO3 t-1. This suggested that the LRBuffer only accounted for the acid generated from dissolution of hydroxide precipitates of Fe and Al. It was found that in order to account for the NAPP of the pitwall material, it was important that the lime required to neutralise the potential acidity (LRNAPP) be added to the LRBuffer to give the total lime requirement (LRTotal) for long-term control of acid generation. A 90 days incubation assessment of selected neutralising materials (limestone, LST; dolomite, DOL; reactive phosphate rock, RPR; fluidised bed boiler ash, FBA) indicated that LST, DOL and FBA were similar in attaining the target pH of 6 at a carbonate content equivalent rate (CER) of 30 kg CaCO3 t-1. The RPR did not raise the pH > 4.5 even at CER of 50 kg CaCO3 t-1 but it was equally effective in overall reduction of EC, SO4 2-, acidity, Fe, Mn and Al in the incubated pitwall rock material. The coarser the grain size, the less reactive the neutralising material was, mainly due to an armouring effect from the Fe and Al hydroxide coatings. While fine-grained material provided quick neutralisation of acid, long-term buffering of the pH may not be possible due to continued generation of acid as more pyrite grains are liberated for oxidation. On the other hand, materials like RPR and coarse LST may provide slow release neutralisation from repetitive dissolution of hydroxide coatings when reacidification occurs. Results of the column experiments on the assessment of ameliorative effectiveness of neutralising materials on leachate quality and subsurface acidity indicated that although application of amendments significantly raised the pH at 0-60 mm column depth, the leachate pH remained below 2.5 throughout the 12 weeks leaching cycle. The concentrations of EC, SO4 2-, acidity, Fe, Mn and Al were however, significantly reduced both in the leachate and subsurface column sections. At depth > 60 mm, the leached columns remained acidic irrespective of treatments. Broadcasted and incorporated methods of application of neutralising material amendments showed similar trends in effectiveness of amelioration. However, the overall ameliorative effectiveness was significantly better with incorporated method of amendments. Surface application of a shallow depth of topsoil (TS) and incorporation of bactericide ProMac (PM) were found effective in the amelioration of low pH conditions of the pitwall rock material by raising pH and significantly reducing sub-surface concentrations of SO4 2-, acidity, Fe, Mn and Al. The amended columns however, still produced effluent pH of <2.5. The overall results from the study indicated that with detailed on-site characterisation and using laboratory studies to formulate appropriate combinations of neutralising materials, the pyritic pitwall rock materials could be suitably modified for plant growth. In practice, the placement of the amendments on the pitwall remains an engineering challenge.Item A description of the soil potassium fertility of steepland pastures in the southern North Island of New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1999) Officer, Sally Jane; Officer, Sally JaneThe pattern of soil K fertility was investigated in two typical steepland pastures, located in the southern North Island of New Zealand. The parent materials of soils in this area are predominantly derived from sedimentary rocks. The soils have medium to high K reserves, and K fertilisers are not normally applied to the areas of steepland pasture. The study sites are part of well-established mixed stock grazing farms and have received regular aerial topdressing with superphosphate for at least 30 years. Grazing animals in steepland tend to favour the flatter areas, which are mainly on the crests of the ridges, and to spend relatively short periods of time grazing the steep slopes. Concerns have arisen as to the development of K deficiencies on the steep slopes, as stock are expected to graze these areas, and then to excrete most of the K ingested in the herbage onto the flatter areas. Two surveys were made of the K fertility patterns in two steepland paddocks. The first study was made over one paddock, by collecting soil samples along vectors of random direction, from points that were between 0.25 m and 25 m apart. The second survey targeted the main trends, sampling at regular intervals along the ridge crests and down the transects of the main slopes, at two paddocks The tests on the soil samples included exchangeable K (Quick test K), acid extractable K and the difference between the two factors, which was thought to provide a measure of plant available nonexchangeable K (Step K). The Quick test K values in one pasture alone ranged from 0.07 to 1.34 mg K/g soil, which was a range between very low and extremely high values for New Zealand soils. There was a similar wide range of values for other parameters. The frequency distributions of the soil test values were skewed, so that the arithmetic mean of the results was higher than 60-70% of the values. Spatial variability was at a maximum at a sampling distance of 0.25 m. The results indicated that the bulking of soil samples was a poor practise when sampling for exchangeable and plant available nonexchangeable K at these sites. Some relationships could be discerned between the soil K fertility patterns and the position of the topsoil in a steepland landscape, despite the high spatial variability. On the steep slopes, the Step K value of a soil was related to the soil moisture pattern, as determined by aspect and water seeps, and also to the pattern of the soil parent materials. Quick test K had no similar relationship to position in the landscape on the steep slopes. The spatial variability of both tests increased as the ground slope decreased. The mean and variability of Quick test K increased sharply on both well drained shoulder slopes and ridge-tops that were animal campsites. In contrast, the mean and variability of Step K increased markedly only on the well drained ridge-top campsites The different behaviour of cattle and sheep, the relatively large amounts of K deposited in excreta compared to P, and the slower rate of breakdown and dispersal of excreta in drier conditions, were all thought to contribute to these effects. The mineralogy of the topsoils at the two sites was also investigated. The clay mineralogy was dominated by a complex of 2:1 layer silicates, accompanied by lesser quantities of quartz, feldspars and kandites. The topsoils formed a sequence, which ranged from a 2:1 layer silicate clay complex that was dominated by mica and interlayered mica smectite (MS), to a 2:1 layer silicate clay complex that was dominated by vermiculite and hydroxy interlayered vermiculite (HIV). There was a very strong relationship between the Step K value and the mica content of a soil on the steep slopes. The relationship indicated that the dominance of either mica and MS, or vermiculite and HIV, in the clay fraction of a soil on the steep slopes depended on the original composition of the soil parent materials, the age of the soil profile, and the soil moisture conditions. On the shoulder slope and ridge-tops, there was a similar range of clay mineralogy, but Step K value now had a poor relationship to the mica content. This effect was mainly associated with soils under the well drained animal campsites, which had a distinctive mica and irregularly interstratified MS dominated clay mineralogy. The results were consistent with a reversal of the 2:1 layer silicate weathering processes under well drained animal campsites. Concentrations of total K and P were investigated in the topsoils of the two steepland pastures. The average difference between the total P of slope and ridge-top samples was about 200 kg P/ha, indicating a relatively small accumulation of P on the ridge-tops after many years of aerial topdressing and grazing. The expected accompanying increase in total K was not found. The marked effect of animal transfer processes on the plant available chemistry and mineralogy of the well drained ridge-top soils was thought to be a disproportionate indicator of the relatively small extent of total nutrient accumulation that appeared to have occurred on the ridge-top campsites. The plant response to K fertiliser was measured at the two steepland pastures sites. No K uptake response or growth response was identified at either site, despite low exchangeable K values in some areas and a low K content in some of the pasture samples, even after fertiliser was applied. In contrast, an exhaustive pot trial, using a selection of soils from the two sites, revealed a considerable range in the ability of the soils to supply K. Cation and anion concentrations were measured in the leachates of "stove pipe" soil cores collected from the ridge-tops and steep slopes. K concentration in the leachates of soil from the steep slopes were relatively low and reasonably consistent over time, compared to the Ca and Mg concentrations that were more sensitive to changes in the ionic strength. K concentration in the leachate of soils from different ridge-top locations varied markedly between the different locations. The increased leaching of K under animal campsites was identified as a significant loss mechanism for the K that is transferred to these areas. However, it was thought that an exact quantification of this process would be difficult, because the spatial variability of the concentration of K leaching from the topsoil into the subsoil under campsites was expected to be even higher than the spatial variability of exchangeable K in these soils. In conclusion, animal transfer losses of K from the steep slopes to the flatter areas at these sites appeared to be in the low range for New Zealand steepland pastures. No significant depletion of the K fertility appeared to have developed on the steep slopes, although the measurements were confounded by the very high degree of spatial variability found in all aspects of the K fertility patterns. The current conventional practice of not applying K fertiliser to these and similar sites was thought to be sustainable.Item Studies on the dynamics of organic sulphur and carbon in pastoral and cropping 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, 2000) Singh, Bhupinder-PalSoil organic matter (SOM) can be depleted or regenerated by altering land management practices. Soil tests capable of reporting the size of dynamic SOM fractions may be useful for indicating the environmental cost of landuse and management practices. Information on the effect of land management practices on soil organic S content and turnover is scarce. This study evaluated the ability of a sequential chemical fractionation procedure to characterise changes in soil S and C organic fractions on a range of pasture and cropping soils with different management histories. The fractionation involved an initial extraction with ion exchange resins followed by dilute (0.1 M NaOH) and concentrated (1 M NaOH) alkali. In addition, recently rhizodeposited 14C (root+exudate derived) produced during a short-term (one week) 14CO2 pulse-labelling study of intact soil cores growing ryegrass/clover pastures, was used to trace the fate of root-derived C in both chemical and density fractionation procedures. In pasture and cropped topsoils, the major amounts of soil S and C were either extracted in 0.1 M NaOH (49-69% S and 38-48% C) or remained in the alkali-insoluble residual fraction (17-38% S and 46-53% C). These two fractions were more sensitive to change caused by different landuse and management practices than the resin and 1 M NaOH fractions. With a large amount of dynamic soil C remaining in the residual fraction it was concluded that increasing strengths of alkali were not capable of sequentially fractionating S and C in SOM into decreasingly labile fractions. The chemical fractionation allocated recent root and root-released 14C amongst all the fractions. Again, most root 14C appeared in the 0.1 M NaOH and residual fractions. Although small in amount, C of higher specific activity (more recently synthesised root C) was preferentially extracted by resin and 1 M NaOH extracts. Density separation was not capable of recovering recent root and root-released 14C in a single fraction. Root-derived 14C was distributed between light (mostly fibrous root debris) (42%) and heavy (organics attached to clay and silt) (45%) fractions. The dispersing reagent soluble fraction recovered <13% of the 14C. An anaerobic incubation and various acids and oxidising agents were tried, in order to recover a greater proportion of root and root-released 14C as a single identity. These were not very successful in either extracting or increasing the alkali solubility of the root C fraction. A 30% H2O2 pretreatment of soil plus roots, or hot 1 M HNO3 treatment of the residual fraction, were more efficient extractants of the root C fraction and should be investigated further to check their ability to better characterise soil organic S and C fractions with a change in management practices. The 14CO2 pulse labelling study of pasture swards showed a greater allocation of recently photo-assimilated 14C to the topsoil layer with a greater proportion of 14C recovered in roots than in the soil. An in situ soil solution sampling technique with mini Rhizon Soil Moisture samplersTM effectively monitored the rapid appearance of a 14CO2 pulse in soil water at various depths. A comparison of the 14CO2 pulse labelling study under light and dark conditions indicated that, in the light lysimeters, 14CO2 photo-assimilation/translocation/rhizosphere respiration was the main pathway for CO2 generation at various soil depths. In the dark lysimeters, 14CO2 diffusion was the main mechanism and 14C assimilation (either photo-assimilation or assimilation by chemolithotrophs in rhizosphere soil) was small. The 14CO2 activity in soil water from four soil depths of dark and light soil cores, and a CO2 diffusion model, were used to identify the 14CO2 contribution from rhizosphere respiration in the light lysimeters. A model was developed, but the unknown geometry of the air-filled pore space in the undisturbed soil cores made it impossible to precisely calculate the contribution made by root respiration to soil water 14CO2 activity.