Phosphorus sorption of some flooded rice soils in Laguna [Philippines]
1996
San Valentin, G.O. | Mosomos, K.S. | Bayot, R.G. (Philippines Univ. Los Banos, College, Laguna (Philippines). Dept. of Soil Science)
Effectiveness of the usual P fertilizer rate recommended for flooded rice is uncertain. Any soil information that may lead to improved fertilizer management practices for flooded rice is therefore important in improving rice yields in the Philippines. In this study, soil samples from flooded rice fields in Laguna were equilibrated with solutions of various P concentration to: determine their P sorption parameters and relationship with some soil properties, and estimate P requirement based on P sorption parameters. The soil samples showed varying pH, clay and organic matter content, 0.5 M NaHCO3 - extractable P content, and P sorption characteristics including P adsorption maximum (K sub max), P retention from a standard 1,000 ppm P solution (P sub ret), and P sorption at equilibrium solution P concentration of 0.02 ppm (P sub 0.02). K sub max and P sub 0.02 were strongly associated with pH. Both P sub 0.02 and K sub max could be predicted by P sub ret. Estimated P requirement generally did not agree with the usual recommendation of 13 kg P/ha. Only 25 percent of the samples showed similar rate of P fertilizer requirement based on P sub 0.02 and Olsen P extraction. For some of the soil samples requiring at least 13 kg P/ha based on Olsen P, the rate of P fertilizer requirement based on P sorption data were very small (4.4 kg P/ha) that perhaps may be ignored until soil P level has significantly decreased
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