Evaluation of Available Phosphorus and Cadmium Associated with Phosphate Rock for Direct Application

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Date
2002
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Abstract
Three greenhouse experiments were conducted to evaluate available P and Cd associated with the use of phosphate rock (PR) for direct application. These experiments were: (1) "Estimation of Phosphorus Availability to Maize and Cowpea From Phosphate Rock as Enhanced by Water-Soluble Phosphorus;" (2) "Modified Iron Oxide-Impregnated Paper Strip (Pi) Test for Soils Treated With Phosphate Fertilizers;" and (3) "Effect of Acidulation of High Cadmium Containing Phosphate Rocks on Cadmium Uptake by Upland Rice." In the first experiment, a medium-reactive Central Florida phosphate rock (PR) was used. The effectiveness of P sources in terms of increasing dry-matter yield and P uptake followed the order of TSP > (PR + TSP) > PR for maize and TSP = (TSP + PR) > PR for cowpea. P uptake from PR in the presence of TSP was higher than P uptake from PR applied alone. With respect to P uptake from PR applied alone, the corresponding relative increase in P uptake from PR due to TSP influence was 165% for maize and 72% for cowpea. In the second experiment, a highly reactive North Carolina PR was used. Both Bray I and the Pi test (with CaCl2) underestimated available P from PR with respect to TSP. Available P estimated by the Pi test with KC1 was more closely related to P uptake with both PR and TSP. More P was extracted from PR by the Pi test with KC1 than with CaCl2, whereas no effect was observed for TSP. In the third experiment, a low-reactive Togo PR and a highly reactive North Carolina PR were used. Both PRs were fully acidulated to SSP and Togo PR was also partially acidulated with H2SO4 at 50% level to PAPR. Cd uptake by rice grain followed the order of NC-SSP > NC-PR and Togo-SSP > Togo PAPR > Togo PR. The results also showed that most of the Cd uptake was retained in rice root and straw. Total uptake of Cd, Ca, and P by the rice plant was higher from NC-PR than from Togo-PR. Cd concentration in rice grain showed no significant difference between NC-PR and Togo-PR, whereas Cd concentrations in root and straw were higher with NC-PR than that with Togo-PR
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Phosphate
Citation
Chien, S.H. 2002. “Evaluation of Available Phosphorus and Cadmium Associated With Phosphate Rock for Direct Application,” Assessment of Soil Phosphorus Status and Management of Phosphatic Fertilisers to Optimise Crop Production, IAEA-TECDOC- 1272, pp. 54-72, International Atomic Energy Agency, Vienna, Austria.
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