Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Has files: YesSubject: search.filters.subject.Superphosphate

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    An evaluation of Chatham Rise phosphorite as a direct-application phosphatic fertilizer : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1982) Mackay, Alec Donald
    Chatham Rise phosphorite (CRP) occurs as nodules on the sea floor some 800 km to the east of the South Island of New Zealand. The phosphate component is a carbonate fluorapatite and the material contains approximately 9% phosphorus (P) and 25% CaCO3. Several lines of evidence suggest that CRP has potential as a direct-application phosphatic fertilizer for pasture. In an initial evaluation in the glasshouse, CRP was found to be an effective source of P for ryegrass when compared to superphosphate over six harvests with four soils. The form (powdered or pelletised) and method (surface applied or incorporated) of application of CRP were found to have a marked effect on the agronomic effectiveness of this P source in the glasshouse. The effectiveness of CRP, when compared at 90% of the yield maxima obtained with superphosphate, which was assigned a value of 100, decreased in the order of powdered and incorporated (100 to 106) > powdered and surface applied (96 to 100) > pelletised and surface applied (85 to 104) > pelletised and incorporated (83 to 90). Results from a comprehensive, long-term field evaluation of CRP at four contrasting sites under permanent pasture over 3 years confirmed and extended the findings of the preliminary glasshouse study with CRP. Apart from some initial differences, pelletised CRP was as effective as superphosphate at all four sites and at two of the hill-country sites (Ballantrae and Wanganui) it showed a marked residual effect in the third year. This was particularly pronounced in the clover component of the sward at these two sites. In fact at these two sites a single, initial application of 70 kgP ha-1 as CRP was agronomically as effective in the third year as three annual applications of 35 kgP ha-1 as superphosphate. This finding has implications to the strategy of fertilizer use. The origin of the marked residual effect shown by CRP at Ballantrae and Wanganui in the third year appears to result from the effect of CaCO3 on the rate of release of P from CRP. The findings that pelletised CRP was almost always as effective as both powdered CRP and superphosphate in the field contrasts with the results of the preliminary glasshouse study with four soils. This discrepancy probably results from the fact that in glasshouse studies a number of factors which can operate in the field and which may contribute to an increased effectiveness of a surface-applied, pelletised phosphate rock (PR) material are excluded (e.g. earthworms). In a glasshouse study, earthworms increased the effectiveness of CRP as a source of P to ryegrass by 15 to 30% over seven hervests. Subsequent studies showed that both the burrowing and casting activity of earthworms indirectly increased the availability to ryegrass of P in the PR by improving the physical distribution and degree of contact of the PR particles with the soil. Interestingly, good agreement was found between the agronomic effectiveness of pelletised CRP in the field and in the glasshouse when earthworms were included as a treatment in the glasshouse. Consequently, care must be taken in extrapolating to the field situation, the results obtained with pelletised PR materials in the glasshouse in the absence of biological mixing. In a comparison in the glasshouse, using six soils and both ryegrass and white clover as indicator species, CRP was as effective as North Carolina phosphate rock (NCPR) and Sechura phosphate rock (SPR), both of which are reactive PR materials. The agronomic data from this glasshouse study were used to evaluate a number of conventional, single chemical-extraction procedures used for assessing the likely agronomic effectiveness of PR materials. Of these, 2% formic acid appears to offer the most promise. However, sequential extraction appears to be necessary with PR materials which contain appreciable amounts of CaCO3. A procedure involving a single extraction with 0.5M NaOH was developed for measuring the extent of dissolution of a PR in soil. Because apatite minerals are largely insoluble in dilute NaOH and because this reagent extracts sorbed inorganic P, increases in 0.5M NaOH-extractable P in a soil to which a PR is added, provide a good estimate of the amount of P dissolved and retained on sorption sites. The extent of dissolution of SPR, measured by NaOH extraction, was found to vary from 22% of added P on the low P-sorbing Tokomaru soil to 48% on the high P-sorbing Egmont soil during incubation at 15°C for 90 days. A high correlation (r = 0.935**) was obtained for the relationship between the dissolution of SPR, measured by NaOH extraction, and the P-sorption capacity of the six soils used. Whereas increasing the P status of the Wainui soil, by the addition of KH2PO4, had no measurable effect on the extent of dissolution of SPR, increasing addition of Ca(OH)2 markedly decreased the dissolution of SPR in this soil. Of the decrease measured in the dissolution of SPR on liming the Wainui soil from pH 5.2 to 6.9, 75-79% of the decrease could be accounted for by the effect of Ca, which also increases on liming. Recults with the Egmont soil indicate that a PR can dissolve at pH 6.5. This suggests that the effect of a higher pH on dissolution is decreased in a soil of high P-sorption capacity. Although the extent of dissolution or SPR increased as the P-sorption capacity of the soils increased, the amounts of water-, Bray-, and bicarbonate-extractable P in the same soils decreased. Of these three estimates of plant-available P, both the Bray and bicarbonate procedures were found to be useful indicators of short-term, plant-available P when SPR and CRP were added to three contrasting soils. Of the two procedures, the Bray procedure accounted for more of the variability, possibly reflecting the difference in the mechanisms by which these two extractants remove P from soil. In contrast, a single water-extraction procedure grossly underestimated the amount of short-term, plant-available P in the soil to which a PR was added. A simple model, based on a modified Mitscherlich equation, was developed to describe and predict the dissolution of SPR in soil. The model, which was developed and evaluated using contrasting soils, appears to have good practical application and should prove useful in future studies of the reactions of PR materials in soils. Although not yet commercially available, CRP appears to have very good potential as a direct-application P fertilizer for pasture and, of particular relevance to hill country farming, it shows a good residual effect. A possible disadvantage is the relatively low P content.
  • Thumbnail Image
    Item
    Investigations into the influence of fertiliser history and climate regime on the soil fertility, soil quality, and pasture production of Wairarapa hill soils :|ba thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1994) Moir, James Laing
    The effects of long-term application of single superphosphate (SSP) on soil plant-available nutrient supply and indicators of soil biological quality was investigated on Wairarapa hill soils ranging widely in previous fertiliser history (from 0 to 250 kg SSP ha-1 yr-1) and climate regime (annual and seasonal rainfall distribution). At 12 field sites spring pasture response to strategic N fertiliser application was measured, while the plant-available nutrient (P, N and S) supplying capacity of the soils was assessed in glasshouse studies. Based on the pasture growth patterns in field and glasshouse studies, a new climate-driven, soil fertility dependent pasture growth model was developed and tested. In addition, the suitability of the Biolog™ GN microtitre plating system was assessed as an indicator of soil 'quality', using these Wairarapa hill country soils. Results of soil analyses indicated that small increases in mineralisable N, in the order of 280 kg mineralisable Nha-1, with increased rates of fertiliser (P and S) may represent inefficient use of P and S fertiliser. Soil mineralisable N increased by approximately 8.6 kg mineralisable Nha-1 for every 1 unit increase in Olsen P. The ratio of accumulated plant-available N:P:S of these soils, resulting from long-term SSP applications, is approximately 17:2:1. Olsen P status was shown to be strongly correlated with measures of plant-available N and S. Pasture growth response in the field to strategic N fertiliser (30 kgNha-1) applied in spring was highly variable across sites, and within the range of 0:1 to 31:1 kgDM kgN-1. Simple single factors representing soil fertility indices, or climatic regime, could not explain the variation in site-to-site pasture growth response to applied N. Factors constraining N response are discussed. In glasshouse studies, on samples of the same soils, ryegrass and white clover showed large yield differences (clover, 0.27-2.29 gDM pot-1; ryegrass, 0.22-2.25 gDM pot-1) on low P status and high P status soils respectively. Glasshouse DM yields did not correlate with those measured in the field, confirming that at field sites yield responses to nutrient availability are strongly modified by (site-specific) climate. The relationship between Olsen P and clover yield in the glasshouse (curvilinear, R2 = 0.80) was similar to that previously seen in (spring) field conditions. The S:P and N:P ratios of clover in the glasshouse trials confirm that P availability in these soils is the major growth-limiting factor, probably followed by S or N, which becomes limiting when P availability is adequate to high. A modified Stanford and DeMent bioassay technique was used to estimate the amount of plant available N, P and S in each soil. Using an exhaustive cropping regime, these soils exhibited a large variation (range) in ryegrass yields when soils were the sole source of P and N. Yields for each soil were strongly correlated with various soil tests for N, S and P availability. S availability to plants was less variable across soils, but the smaller variation in S limited yield was still strongly correlated with the variation in a newly developed soil hydrogen peroxide-extractable S test. Results from both glasshouse experiments provide strong evidence that the Olsen P soil test is a valuable soil fertility indicator of plant-available P, N and S on legume-based pasture soils with a history of superphosphate use. The amount of dry matter production, when considered with the quantity of soil used for each treatment (-N, 100g; -P, 50g; -S, 25g), suggest that these soils have large pools of plant-available or mineralisable P and S, and, relative to plant demand, small pools of soil mineralisable N. A four-fold increase in field DM production resulted from a 3-fold increase in soil mineralisable N at these sites. This suggests that the rate of N cycling probably also increases with yield increase, and that the size of the soil mineralisable N pool is not directly related to pasture N supply. A new climate-driven, soil fertility dependent pasture production model has been developed and tested using actual DM yields from the field trial sites. The model assumes that pasture growth is proportional to evapotranspiration, and that the proportionality constant (k) depends on soil fertility Pasture growth per mm of evapotranspiration was strongly related to soil available P status at these sites. From results of the glasshouse study, it was concluded that Olsen P was a strong indicator of 'general' (plant-available P, N and S) across these sites, and therefore suitable for use as the soil fertility proportionality constant in the pasture production model. Soil-limited evapotranspiration is calculated from a simple daily soil water balance model. Values for k varied from 11 to 19 kg DM ha-1 mm-1 of evaporation. With the exception of growth after severe drought conditions, the model shows potential to closely predict actual pasture yield. It is hoped that discrepancies between the modelled and measured production may lead to useful speculation and further research on the interacting effects of weather and fertility on pasture growth. The Biolog™ GN microtitre plate system, for comparing substrate use patterns of 95 single C compounds was assessed as an indicator of soil microbial functional diversity across the 12 test hill soils. Preliminary studies showed that saline extracts of different fertility status pasture soils used for Biolog™ microtitre plate assay inoculation contain significant amounts of readily available C. It was concluded that in order to interpret the substrate use patterns correctly, this effect must be corrected for. The Biolog™ microtitre plate system, for use as an indicator of soil quality and health, was shown to have limited application to this range of pasture soils with differing pasture histories. Adaptive factors, such as constitutive and inducible enzyme activities, were shown to complicate the interpretation of microbial growth on the C substrates. Substrate use patterns also changed when soils were rewetted and incubated. Possible 'indicator' substrates were identified, but it was concluded that these were low-energy decomposition products, and as such, are not useful as indicators of microbial functional diversity across these soils. Further research would be required to establish how stable the substrate use patterns are, or the relevance of these indicators to field soil processes. However, as a research tool, the Biolog™ assay showed potential to separate these soils on the basis of microbial functional diversity. The direction of future research, and limitations of current techniques used in this field are discussed.