Primary and residual Effects of Rock Phosphates and Their Correlation with P-Test Value of Rice Soil

Abstract

Two consecutive pot experiments were conducted to study the primary and residual effects of rock phosphate fertilizer from 6 different origins on lowland rice. Four commonly used methods for determining “ available” phosphors in soil were also used to evaluate their effectiveness in phosphorus in soil were also used to evaluate their effectiveness in predicting the response of rice to the phosphate fertilizers. The rice plant responded markedly and significantly in terms of straw yield, phosphorus concentration of straw and total phosphorus uptake in straw to the rock phosphate fertilizers in both plantings. Highest responses were obtained with the Horth Carolina rock phosphate while lowest responses were obtained with the Missouri rock phosphate. Straw yield, phosphorus content of straw and total phophorus content of the soil as determined by the Bray I and Olsen method. The Bray II and Truog methods also gave P-test values that show significant correlation with the responses of the rice plant but the correlations were not as pronounced as those obtained with the Bray I and Olsen methods. The correlation coefficients obtained with the four methods of phosphorus determination rank as folows – Bray I >Olsen>Bray II>Truog.