Browsing by Author "Officer, Sally Jane"

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    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 Jane
    The 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.
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    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 Jane
    The 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.