Optimizing Phosphorus Fertilization Rates for Soybeans Grown on Oxisols and Associated Entisols
1985
Lins, I. D. G. | Cox, F. R. | Nicholaides, J. J.
Although soils vary considerably in their P sorption characteristics, this factor is often not considered in a soil test interpretation. One soil property closely related to P sorption is clay content. Residual P studies were conducted for 4 yr on three tropical soils of similar clay mineralogy, two Oxisols of 63 and 27% clay, and a Quartzipsamment of 12% clay. The Mehlich 1 (1:10) extractable P level was described as a function of time, initial soil P level, and P fertilization rate. One crop of soybeans [Glycine max (L.) Merr.] was grown each year and the yield related to extractable P, which, in turn, was related to the initial P soil level and P fertilization rate for a period of 1 yr. Based on a soybean price of $0.23/kg and a fertilizer P price of $1.23/kg, rates of P were calculated for each of the three soils that would maximize net returns for various initial levels of extractable P. As these rates differed markedly with clay content, a soil test interpretation was created by multiple regression based upon both Mehlich 1 extractable P concentration and clay percentage to predict a recommended rate of fertilizer phosphorus (R) as follows: R = 80 − 2.57(soil P) + 0.01386(clay)² − 0.003281(soil P)(clay²). This function should be applicable to many soils with similar clay characteristics.
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