Quantitative evaluation of the availability of rock phosphate applied to acid sulphate soils using isotope technique I. effect of time of rock phosphate application on phosphorus A-value
1984
Chanthana Siriphaibun | Pathum Sanitwong na Ayutthaya (Department of Agriculture, Bangkok (Thailand). Agricultural and Chemistry) | Phonphimon Chaiwannakhup
Effect of time of Thai rock phosphate fertilizer application on the availability of phosphorus was studied on three typical acid sulphate soils of Central Plain, namely Rangsit very acid, Ongkarak and Sena in the greenhouse using the A-value method. Rock P fertilizer was applied into the soil at transplanting and into moist soils 3 months prior flooding and transplanting. The results showed no significant differences in availability of phosphorus derived from rock P as measured by the A-value with time, although the A-value of high grade rock P in Rangsit very acid soil was slightly greater. It was indicated that high grade rock P reacted more effective in acid sulphate soils, resulting in increased dry matter production of rice plant and its utilization of applied rock P when compared to triplesuperphosphate fertilizer (TSP). The A-values of applied TSP in Lopburi soil (pH 6.1, non acid sulphate) were found to be close to that of rock P, and the produced dry matter was markedly greater as expected. The utilization of rock P in acid soils observed at primordial initiation growth stage was 1.6 - 2 % whereas it was found 1 % in Lopburi soil. When TSP was applied in very acid soils, i.e., Rangsit very acid, Ongkarak, the utilization of applied P was found decreasing 2-3 folds of that applied in soil pH 4.
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