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    Prediction of soil Olsen P through mixed pasture leaf tissue biochemical and biophysical properties, topography and farm management in New Zealand hill country : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agricultural Science at Massey University, Turitea, New Zealand
    (Massey University, 2019) McVeagh, Philippa
    In New Zealand hill country, soil Olsen Phosphorus (P) is a key piece of information used to decide rates, products and areas to which aerial applications of phosphate fertilisers are made. Laboratory based soil Olsen P measurements are made on bulked soil cores collected along transects, laid out across slope faces. On most hill country farms, aerial fertiliser applications are applied uniformly over large blocks or the whole property. Accurate, detailed soil maps are scarce, but essential for site specific nutrient management. Current soil sampling techniques provide spatially sparse information and attempts to interpolate point measurements of soil properties in hill country, have not been successful. The potential improvement in nutrient use efficiency would lead to increases in pasture production and quality, and an increase in production of meat and wool produced off the same land area. As sheep and beef production is forced from more productive land into more marginal areas by other land uses, managing hill country landscapes efficiently will become critical for the sheep and beef industry. Increases in global food demand, a growing interest in product origins and production practices by the consumer, and tightening of environmental regulations will further put pressure on these systems. Appropriate soil and fertiliser management has suffered from a lack of information to make sound decisions. Maps of soil Olsen P are a first step, with much potential in the applications of hyperspectral imaging yet to be discovered. The objective of this thesis was to develop a model that could be applied to readily available data layers, to make continuous predictions of phosphate availability in the soil (Olsen P) across New Zealand hill country farms. This research was one part of a larger project that firstly aimed to derive estimates of pasture parameters from hyperspectral imagery. This information could then be used in conjunction with ancillary data to determine soil nutrient status. Finally, this information would be used to inform variable rate fertiliser applications through a prescription map loaded into a computer controlled aerial top dressing system. A multi-site, multi-seasonal database from eight commercial hill country farms incorporating a range of leaf tissue nutrient concentrations, pasture biophysical properties, and topographic, soil and farm management information was built up alongside soil chemical properties. Model development was based on in-situ measurements and laboratory analysis of leaf tissue and soil samples collected on 0.5m x 0.5m plots. A total of 3,030 plots were sampled in the autumn and spring. Simple plant P indices are usually used on single species samples of actively growing tissue. Here they were used on mixed pasture samples at various stages of maturity with mixed success. Although overall correlations were weak, leaf tissue P concentration and PNI were more strongly correlated to soil Olsen P than the P:N ratio or PNIc. Soil Olsen P was more strongly correlated to leaf tissue P concentration and PNI in spring (R² = 0.21 and 0.24 respectively) than in autumn (R² = 0.12 and 0.12) and both seasons combined (R² = 0.13 and 0.13). For individual sampling events, all P indices were generally more strongly correlated to soil Olsen P in spring than in autumn. Of the individual sampling events, the strongest correlation was at the hill country farm Cleardale in the spring (R² = 0.56) using leaf tissue P concentration. The database was then used in exploratory analysis to identify important input variables across farms and seasons through stepwise multiple linear regression. Leaf tissue P and copper concentration, slope, fertiliser history, the proportion of green tissue in the sample and seasonal information were consistently selected. For all seasons and farms combined, 13 variables (slope, 30 day rainfall, soil moisture deficit, time since the last fertiliser application, rate of the last fertiliser application, leaf tissue P, Cu, Na, Mn and Zn concentrations, DM%, the dead vegetation fraction and legume content) were selected as predictors for soil Olsen P with an R² of 0.42 for the mean of the 5 plots at each site. For season specific models, different sets of predictors were selected and achieved higher levels of explanation, R² of 0.45 in autumn and R² of 0.50 in spring for the mean of the 5 plots at each site. The approach taken to predict soil Olsen P was to develop Bayesian hierarchical multiple linear regression models. Models were developed using different parameters and hierarchical structures. The pasture biochemical and biophysical parameters along with topographic and farm management factors all contributed significantly to the model. The model fit was significantly increased and the residual error greatly reduced in the combined model compared to models containing only plant biochemical and biophysical or only physical inputs. The posterior predictive distribution from a Bayesian hierarchical multiple linear regression model provided an estimate of soil Olsen P and the uncertainty of the prediction made. A leave-one-out-cross-validation showed an improvement compared to an average value used to inform the most basic and risk averse uniform fertiliser application as a benchmark. The Bayesian hierarchical model can be used for predictive soil mapping, which was demonstrated, however still needs to be validated. Predictive soil mapping exhibited the potential of using input data layers derived from hyperspectral imagery and digital elevation models, to provide continuous predictions of soil Olsen P across a hill country farm. Maps of soil Olsen P were produced, where methods attempting to use interpolation techniques in hill country have been unsuccessful. These maps provide vast amounts of data compared to traditional spatially sparse soil sampling. Soil phosphate availability has a significant effect on pasture productivity, and species composition which affects pasture quality. As considerable research and programmes have focused on genetics and breeding for animal performance, it is now thought that pasture productivity and management is restraining the potential performance of sheep and beef systems. Of the factors driving pasture productivity, fertiliser applications are one factor farmers have control over. The levels of P available in soils observed in this study suggest that much potential exists to increase pasture production and quality through increasing P availability in the soil. In summary, a Bayesian hierarchical linear regression model significantly improved the predictions of soil Olsen P made across hill country farms compared to a benchmark traditional uniform approach. From this Bayesian hierarchical model, estimates of soil Olsen P can be made on locations and time points outside of the dataset with a known level of uncertainty. This model can be used in predictive soil mapping to produce maps of soil Olsen P across hill country farms.
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    A comparison of two phosphorus soil tests as inputs to a pasture growth model : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Soil Science at Massey University
    (Massey University, 1979) Smith, Robert Grey
    Glasshouse and field studies were carried out to investigate relationships between plant growth and extractable soil phosphorus and between fertilizer phosphorus and extractable soil phosphorus respectively. The purpose of the studies was to provide information with which to quantify the parameters of a simple model designed to predict relative pasture yield as a function of soil and fertilizer phosphorus. The relationship between yield and water-extractable soil P differed markedly between two soils of different P retention properties in glasshouse studies using both intact cores and conventional pots. To illustrate this difference, the levels of water-extractable P (0-8 cm depth) in intact cores required for 90% of maximum yield were 12.7 and 2.6 μg/g soil in the soils of lower and higher P retention respectively. In contrast, the relationship between yield and Olsen (bicarbonate-extractable) P was much less soil type dependent. The corresponding levels of Olsen P in intact soil cores required for 90% of maximum yield were 17.7 and 17.8 ug/g soil respectively. For modelling purposes, the Olsen procedure was therefore considered to provide a more suitable index of plant available soil P from which to predict pasture production on soils differing in P retention. The proportion of yield variation accounted for by differences in extractable soil P was 25% or less in initial harvests from the intact cores, 50-75% in later harvests from the intact cores and 89-97% in the pot experiments. The results of the intact core experiments, however, were considered to be more directly applicable to the field situation than were the results of the pot experiments. Seasonal changes in extractable soil P in Tokomaru silt loam included an increase during the dry season to reach a peak in late autumn followed by a decline in winter. The magnitude of these changes with respect to Olsen P was approximately 2.5 and 5 μg/g soil in the 0-8 cm and 0-4 cm depths respectively. A subsequent decline in extractable soil P during the spring and second summer was attributed largely to plant uptake of soil P and its loss in discarded clippings. The application of superphosphate increased extractable soil P in proportion to the rate applied. The increases per unit of applied fertilizer P, in both absolute terms and relative to an initial (time-zero) increase, were greater in a soil of low P retention (Tokomaru) than in a soil of high P retention (Ramiha). Water-extractable P (0-8 cm depth) was increased on average by 2.3 and 0.2 μg/g in the Tokomaru and Ramiha soils respectively six months after the application of 40 kg P/ha as super-phosphate. The corresponding average increases in Olsen P (2.7 and 1.1 μg/g) were greater, and differed less between the soils, than the increases in water-extractable P. Thus, neither soil P extraction procedure was independent of soil type in terms of the effects of applied fertilizer P. For modelling purposes the effects of applied fertilizer would need to be assessed in a wider range of soils. The level of water-extractable P in stored, air-dry soils was found to undergo short-term fluctuations, apparently due to changes in the conditions of extraction such as variations in the pH of distilled water. Longer-term increases of 25-100% in the level of water-extractable P of stored soils also occurred. No reason for the latter changes was apparent.
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    A comparative study of the phosphorus characteristics of oil palm volcanic soils in Papua New Guinea and New Zealand volcanic soils : a thesis presented in partial fulfillment of the requirements for the Degree of Master of Applied Science in Soil Science at Massey University
    (Massey University, 1998) Banabas, Murom
    Oil Palm (Elaeis guineensis Jacq.) grown on volcanic ash soils in Papua New Guinea (PNG) generally respond well to N fertilisers but shows a lack of consistent response to inorganic phosphorus (P) fertilisers. This is true even on soils with high phosphate retention (PR) and where Olsen P values highlighted in the preliminary survey of PNGOPRA field trial data are very low (<10 mg/kg). A notable exception occurs at Bialla (Trial 201) where significant responses (yield and growth parameters) to P fertilisers have been found on soils with very low Olsen P (<4 mg/kg) and very high PR values (>90% to at least 60 cm depth). This study was done to characterise the PNG oil palm growing volcanic soils in relation to P responsiveness, to identify P fractions and their relative amounts, to determine the fate of applied P fertilisers and to compare chemical and mineralogical characteristics of PNG soils with some New Zealand (NZ) equivalent soils. Mineralogical analysis indicates that the PNG soils used in this study are relatively young as evidenced by the presence of very high amounts of readily-weatherable volcanic glass in the sand, silt and clay fractions. Soils at Hoskins, Kapiura and Bialla, all in West New Britain (WNB) Province, contain similar amounts and types of primary and secondary minerals. Soils at Bialla are probably older than those at Hoskins and Kapiura and contain large amounts of secondary amorphous minerals (allophane and ferrihydrite) in the clay fraction. Soils at Popondetta are different from those in WNB with high amounts of hornblende and no augite or hypersthene in the heavy mineral fraction. Allophane levels in the clay fraction are high to very high in soil surface layers at Hoskins and Kapiura and at all depths in Bialla soils. At Popondetta, allophane content is very low at all depths PR in all soils and at all depths was highly correlated with acid oxalate extractable Al (Alo) (r = 0.84*) and iron (Feo) (r = 0.89*). The sources of these 2 extracts (allophane and ferrihydrite) are largely responsible for the high PR in the soils studied. High allophane and ferrihydrite levels at all depths in Bialla soils correspond well with very high PR values ( >90%) to at least 2 m depth. Low levels of these 2 minerals in Popondetta soils correspond well with low PR values (30%). Intermediate PR values (60 - 70%) for Hoskins and Kapiura surface soils correlates well with the occurrence of intermediate levels of allophane and ferrihydrite. In all PNG soils, a P fractionation scheme showed that the major P fractions are organic. At Hoskins, NaOH-Po accounts for 38 to 48% of total P. For Kapiura NaOH-Po accounts for approximately 50% of total P, and Bicarb.-Po accounts for 59% of total bicarbonate-extractable P. For Bialla soils, NaOH-Po and Bicarb.-Po comprise between 74 and 76%, on average, of their respective total extracted P for all depths. At Popondetta, NaOH-Po comprises 62% and Bicarb.-Po 63% of their respective total extractable P contents. P fertiliser accumulation in Hoskins and Kapiura soils occurs mostly in organic forms and within the top 10 cm of soil. At Hoskins, 83% of total added P accumulated in the top 10 cm (53% being NaOH-Po) while 17% was found in the next 10 cm depth (31% being NaOH-Po). At Kapiura, 74% of total accumulated P was found in the top 10 cm of soil (61% being NaOH-Po) and 26% within the 20 - 30 cm layer (81% being NaOH-Po). The presence of amorphous minerals explains much of the behaviour of P in trial soils, with the major P source/sink in PNG soils being as organic forms. In relation to soil mineralogical and chemical characteristics, PNG soils were classified into one of the major 3 groups in terms of responsiveness to P fertilisers; (a) soils with very high PR (>90%) and Olsen P values of less than 4 mg/kg which are considered most likely to respond to inorganic P fertilisers e.g. Bialla soil, (b) soils with medium to high PR (60 - 70%) will likely show inconsistent responses to P fertilisers and P responses are most likely to be secondary to N e.g. Hoskins and Kapiura soils and (c) soils with low PR (30 - 40%) which are unlikely to respond to P fertilisers at least in the foreseeable future e.g. Popondetta soils. This study highlights a future need for further study of the dynamics of P nutrient cycling, specifically the mineralisation rates of organic matter and the release of Pi for plant uptake in PNG oil palm growing soils. Also there is a need to re-establish the leaf critical concentration because in PNG soils though leaf levels are generally less than 0.150% DM, palms do not always respond to P fertilisers. This suggests that the "critical" P concentrations under PNG conditions is probably less than the international standard at 0.150% DM. Mineralogical and P sorption characteristics of young volcanic ash soils in NZ are sufficiently similar to those in PNG to provide useful information about the general behaviour of P fertilisers and P reaction products in oil palm production systems.