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    Potential uses of fluidised bed boiler ash as a liming material, soil conditioner and sulphur fertiliser : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1996) Wang, Hailong; Wang, Hailong
    A fluidised bed boiler ash, produced by the New Zealand Dairy Corporation (NZDC FBA) as a by-product resulting from the combined combustion of high S coal and limestone, was chemically characterised and evaluated as a potential liming material, soil conditioner and S source in some representative New Zealand soils. Chemical analysis showed that slaked NZDC FBA had a pHwater of 12.4 and CaCO3 equivalent of 51.8%. The "lime" in FBA is mainly Ca(OH)2, making it a quicker acting, more caustic material than limestone. FBA contained 6.2% S, 25.4% Ca (dry weight basis) and negligible amounts of P, K and Mg. Mineralogical analysis indicated that approximately 50% of the S in the slaked FBA is gypsum (CaSO4.2H2O) with the remainder being water insoluble ettringite (Ca6Al2(SO4)3(OH)12.26H2O). A field trial was established on a permanent dairy pasture (predominantly ryegrass (Lolium perenne) and white clover (Trifolium repens)) on peat soil, in Moanatuatua peatland, Waikato, New Zealand, to examine the effectiveness of FBA as a soil conditioner to overcome soil water repellency, a liming material and a S source. The treatments included the untreated control and three rates of FBA (1000, 6616 and 26462 kg FBA ha-1, wet weight basis), which were surface dressed onto the pasture. Three rates of lime, which had the same CaCO3 equivalent as the corresponding rates of FBA, were included for comparison. Using the molarity of ethanol droplet (MED) test, the air dried peat soil sampled in summer was classified as severely water repellent (MED > 2.2). Fatty acids were identified as the fraction most responsible for the repellent character of the peat soil. Only the high rate (26462 kg ha-1) of FBA significantly reduced water repellency of surface peat soil and increased the rate of water infiltration into the dry peat. The hydrophobic nature of the peat soil was probably modified by the high alkalinity of applied FBA, which removed or saponified fatty acids from the soil particle surface. However, normal liming and fertiliser rates (6616 kg ha-1 or less) of FBA application, as well as all the lime treatments, had negligible effect on the water repellency of the peat soil. Therefore, it is not practical to use FBA as an amendment to minimise water repellency on peat soil. The FBA treatments significantly increased pasture yield, in the field trial during eight months of the experimental period, mainly by improving herbage S nutrition status. In spring, the S concentrations in herbage from the FBA treatments were raised from a deficient level of 0.20% S (the untreated control) to 0.27 - 0.40% S. The ettringite-sulphate in FBA acted as a slow-release S fertiliser and high rates of FBA application maintained the raised S concentrations in the herbage for the eight month period. The presence of ettringite implies that application of FBA-sulphate has the potential to reduce the leaching loss of sulphate, a common problem in many New Zealand soils. In a laboratory incubation and leaching study using repacked peat soil cores, the effect of surface applied FBA and lime on base and solute movement in soil was investigated. The results indicated that FBA was an effective alternative to agricultural lime to neutralise the acidity of peat soil. Although surface-applied FBA had no significant effect on decreasing subsurface soil acidity as measured by pH change in the peat soil, the Ca2+ ions released by FBA dissolution moved down to subsurface soil much faster than those released from lime. Increased Ca2+ ion concentration in subsurface soil can alleviate the acidity constraints on pasture root growth through the antagonistic relationship between Ca2+ and H+ ions. In contrast to the lime treatment, however, FBA caused significant leaching of native soil exchangeable K+. Therefore, K fertilisers should accompany FBA application to peat soils. In order to examine the effect of topsoil incorporated FBA on the subsurface acidity in mineral soils, six acidic topsoils (0 - 100 mm) were tested for their ability to "self-lime" through sulphate sorption from gypsum treatment. Two soils, from the yellow-brown loam, or Allophanic soil (the Patua soil) and the yellow-brown earth, or Ultic soil (the Kaawa soil) groups (orders), which contrasted strongly in their reaction to gypsum treatment, were chosen for further study. Lime, FBA and Flue gas desulphurisation gypsum (FGDG) were incorporated in the top 0 - 50 mm of repacked columns of the Patua and Kaawa soils, at rates containing Ca equivalent to 5000 kg ha-1 of CaCO3. Each column was leached with 400 mm of water. After leaching, one set of the columns were sliced into sections for chemical analysis, and another set was used for growing lucerne (Medicago sativa. L) as a root bioassay. In the columns of the variable charged, allophanic Patua soil, topsoil incorporated NZDC FBA ameliorated top and subsurface soil acidity through liming and the "self-liming effect" induced by sulphate sorption, respectively. The soil solution pH of the top and subsurface layers of the Patua soil were raised to pH 6.40 and 5.35 respectively, by the FBA treatment, compared with pH 4.80 and 4.65 in the control treatment. Consequently phytotoxic labile monomeric Al concentration in soil solution of the FBA treatment was reduced to less than 0.1 µmol Al dm-3, compared with that of 8 - 64 µmol Al dm-3 in the untreated control. These changes were associated with greatly improved lucerne root growth in the subsurface of the Patua soil after FBA treatment. FGDG had a similar "self-liming effect" on subsurface of the Patua soil, but not the topsoil. Whereas FBA raised the pH of the Kaawa topsoil, no "self-liming effect" of subsurface soil by sulphate sorption was observed on the Kaawa soil, which is dominated by permanently charged clay minerals. Application of FBA and FGDG to both soils, however, caused significant leaching of native soil Mg2+ and K+. These nutrients were displaced from the exchange sites by the relatively high concentration of Ca2+ released from dissolution of gypsum. In contrast, the topsoil incorporated lime had little effect on either the subsurface soil acidity or nutrient leaching. NZDC FBA is an ideal by-product for correcting topsoil and subsurface soil acidity in yellow-brown loam (allophanic) soils, but only topsoil acidity on yellow-brown earth (Ultic) soils, dominated by clays with permanent charge. Mg and K fertiliser application would be recommended when a soil is treated with FBA or other gypsiferous materials.
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    Impacts of phosphate fertiliser application on soil acidity and aluminium phytotoxicity : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1997) Manoharan, Veeragathipillai
    New Zealand's agricultural production systems are based largely on legume-based pastures which require a high soil phosphorus (P) status to achieve optimum production. Although application of P fertilisers undoubtedly leads to increased agricultural production and a direct economic benefit to New Zealand, concerns are growing about possible harmful side effects of long-term application of high rates of P fertilisers. These side effects can arise through contaminants contained in the fertilisers and through the direct or indirect effects of the P fertilisers on soil acidity. The general objective of the present study was to investigate the effect of long-term application of P fertilisers on soil acidity and aluminium (Al) phytotoxicity. Particular emphasis was placed on the possible role of fluoride (F), contained in the fertilisers as a contaminant, on the chemistry and phytotoxicity of soil Al. A field study was carried out to investigate the effects of long-term annual applications of six types of P fertilisers on soil acidity under legume-based pastures. The results from this study indicated that in a marginally acidic soil (pH(H2O) 5.4-5.8), irrespective of the rate or form of P fertiliser used, the soil became increasingly acidic over a period of seven years. However, the rate of acidification varied with the type of P fertiliser used. By year 8, the application of North Carolina phosphate rock (NCPR) gave higher pH, exchangeable Ca and Ca saturation but significantly lowered exchangeable and soluble Al than the control plots. In contrast, diammonium phosphate (DAP) application gave significantly lower soil pH, exchangeable Ca and Ca saturation and increased soluble Al and exchange acidity. In comparison to the control plots, single superphosphate (SSP) in general had similar soil pH and exchangeable Al but increased exchangeable Ca and Ca saturation at higher rates of application. The results suggested that continuous use of certain reactive phosphate rocks such as NCPR can significantly slow down the rate of acidification of pastoral soils. Using the same field trial, changes in soil solution composition and Al speciation were investigated. Application of DAP and high rates of SSP increased total Al concentrations in the soil solution even though SSP had no effect on soil pH. The increased Al concentration in the SSP treatments could be due to high concentrations of F (added as a contaminant in the fertilisers) complexing Al, and hence bringing more Al into the soil solution. Application of NCPR decreased total Al concentrations, presumably by increasing pH. Application of DAP increased the predicted concentrations of toxic Al species- Al3+, Al(OH)2+, Al(OH)2 1+. In contrast application of SSP decreased the toxic Al concentration, despite higher solution Al concentration compared with control treatment. The concentration of toxic Al species in NCPR-treated soil was also lower than in the control treatment. A short-term bioassay was carried out using barley (Hordeum vulgare L.) to study the effects of long-term (20 years) inputs of Ca, F, and sulphate (SO4)from P fertilisers and changes in soil pH on Al phytotoxicity. Results of this glasshouse experiment showed that the relationships between soil Al indices and barley root growth were different for soils with different P fertiliser history. The inability of total monomeric Al, and 0.02 M CaCl2-extractable Al to explain the variation in root growth in the combined data for fertilised and unfertilised soils indicated that the relative proportions of the phytotoxic Al were different for fertilised and unfertilised soils. These differences were due to the higher proportions of the less-toxic Al-F complexes in the fertilised soil and also due to the high concentrations of Ca in the soil solution. The ability of the activity ratio of Al3+/Ca2+ to predict Al toxicity most consistently across soils with different P fertiliser histories indicated that soil solution Ca should be taken into account together with toxic Al species in the assessment of Al phytotoxicity. A short-term bioassay was carried out to develop a chemical test to predict the potential toxicity of Al for early root growth in widely different soil types. The results from this study showed that, in soils with similar physical properties, mineralogy and low organic matter content, short time pyrocatecol violet (PCV)-Al determination in soil solution can be used as a simple and reliable method to predict Al toxicity. However, the direct use of short-time colorimetric procedures to predict critical Al toxicity levels for different soil types could be limited by the variations in organic Al and other factors such as ionic strength, cation and anion types and concentrations. Among the Al toxicity indices studied, as observed in the trial with similar parent materials, the activity ratio of Al3+/Ca2+ is again the best predictor of Al toxicity but now in widely different soil types. The interactive effects of soil acidity and F were also studied using the short-term bioassay method. Increasing rates of F additions to soil significantly increased the soil solution concentrations of Al and F irrespective of the initial soil pH. However, the rate of increase was much higher at low pH than at high pH. There was a significant interaction between soil acidity and F on root growth of barley. High rates of F addition severely reduced root growth and the effect was more pronounced in the strongly acidic soil. Speciation calculations predicted that increasing rates of F additions increased Al-F complexes in the soil solution. Results also indicated that Al-F complexes are not toxic at lower concentrations but they are toxic at high concentrations and the relative toxicity depended on the type of Al-F complexes present. Results from this study suggest that it is unlikely that in a marginally acidic soil (pH (H2O) 5.4-5.8) long-term F inputs via P fertilisers will have any detrimental effects on plant growth. Rather it will reduce the free Al concentration while keeping the Al-F species concentration below the toxic threshold level in the soil solution, thereby reducing the occurrence of Al phototoxicity.
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    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, Shivaraj
    The 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.