Characterisation of phosphate rock reactivity and implications on management practices in Malaysia
1997
Chan, K.S. | Goh, K.J.
The reactivity of four phosphate rocks (PR), finely ground to 100 mesh, were estimated by their solubilities in 2% citric acid, 2% formic acid and by incubation in two Malaysian soils. In the incubation experiment, the PR, at equivalent rates of 125, 250, 500 and 1000 mg P kg E-1 soil, were incubated in soil, thoroughly wetted, at ambient temperature for over eight weeks. The dissolution of PR was determined by measuring the difference in extractable calcium between treated and untreated soils using BaCl2 triethanolamine this being commonly called the delta calcium (Ca) technique. Results of the incubation experiment showed that dissolution of PR decreased exponentially with increasing application rates. Using logarithmic transformation of the PR rates, a linear relationship was obtained. PR dissolution was generally better in the more acidic Rengam series soil. However, when high rate of a reactive rock was used, the soil C.E.C became the dominant factor controlling the dissolution rate. The PR dissolution rate was also found to be better correlated to formic acid solubility than to citric solubility. Formic acid-P was found to provide a good index of the reactivity of PR. These experiments also indicated that the choice of PR for plantation crops depended on the soil properties and application rate. At high rate, the PR should be applied evenly and broadly to improve its dissolution rate.
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