A decrease in soil pH causes the concentration of exchangeable aluminium (Al) in soil to increase which is toxic to plants and binds to the essential plant nutrient phosphorus (P), making it less available. Oxidised acid sulfate soils have pH values <4 and based on observations in the field it was hypothesised that decreased exchangeable Al and increased available P following compost application could be attributed to: the functional group profiles of organic acids from composting different materials; the increase in pH from the neutralisation of acidity by compost and/or addition of P from compost application. Further, it was hypothesised that these changes to ASS chemistry will result in increased yield following compost application in the field. In the laboratory, no correlations were found between any measured, compost derived functional group and a decrease in Al and/or maintenance of P concentration in a solution akin to ASS. A very strong relationship was found, however, between the decrease in Al and maintenance of P in the solution and the total P concentration of the compost. Four laboratory incubation experiments in actual ASS determined the influence of functional groups, pH and P addition resulting from compost application to ASS. Lime without compost had the greatest influence on the exchangeable Al concentration and no additive benefit of co-application of lime with compost was found. Filtercake compost had the greatest effect on available P concentration, regardless of the co-addition of lime or P. In the presence of compost and lime, adding P did not have a benefit to exchangeable Al, pH or available P. Field experiments confirmed that filtercake compost was effective in increasing soil pH and plant available P, decreasing exchangeable Al. Saleable yield, dry matter yield and leaf P of baby corn also increased. The results indicate that compost is a conceptually viable ameliorant of ASS. It is thought that calcium phosphates in filtercake compost are dissolved at low pH resulting in a binding of Al by P and further P being made available for plants.
|Qualification||Master of Philosophy|
|Place of Publication||Australia|
|Publication status||Published - 2018|