Long-term residual value of North Carolina and Queensland rock phosphates compared with triple superphosphate |
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Authors: | M D A Bolland and R J Gilkes |
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Affiliation: | (1) Plant Industries, Western Australian Department of Agriculture, 3 Baron-Hay Court, 6151 South Perth, WA, USA;(2) Soil Science and Plant Nutrition, Faculty of Agriculture, University of Western Australia, 6009 Nedlands, WA, Australia |
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Abstract: | The effectiveness of large single applications of North Carolina reactive rock phosphate, Queensland non-reactive rock phosphate, and Calciphos, were compared to the effectiveness of superphosphate in field experiments in south-western Australia for up to 11 years after application. As measured using plant yield, superphosphate was the most effective fertilizer in the year of application, and relative to freshly-applied superphosphate, the effectiveness of the superphosphate residues declined to be about 15 to 65% as effective in the year after application, and 5 to 20% as effective 9 to 10 years after application. Relative to freshly-applied superphosphate, all the rock phosphates were 10 to 30% as effective in the year of application, and the residues remained 2 to 20% as effective in the 10 years after application. The bicarbonate soil test reagent predicted a more gradual decrease in effectiveness of superphosphate of up to 70% 10 years after application. For rock phosphate, the reagent predicted effectiveness to be always lower than for superphosphate, being initially 2 to 11% as effective in the year after application, and from 10% to equally as effective 10 years later. Therefore rock phosphates are unlikely to be economic alternatives to superphosphate in the short or long term on most lateritic soils in south-western Australia. |
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Keywords: | bicabonate-extractable-soil-phosphorus relative effectiveness residual value rock phosphate superphosphate Avena sativa Hordeum vulgare x Triticosecale Trifolium subterraneum |
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