Residual Effects of Phosphorus Applications on a High Phosphorus Adsorbing Oxisol of Central Brazil

High crop yields on P‐deficient Oxisols are not possible without application of relatively high amounts of fertilizer P. Correction of P deficiency can be accomplished by an initial broadcast application of a high rate of P or by lower rates of P applied as a band treatment or combination broadcast and band treatment. The residual effect of such P applications is influenced by the rate and method of application. A field study was established on a Haplustox in the Cerrado of Contral Brazil to evaluate the residual value of applied P as measured by corn yields and soil P analyses. Comparisons were made of the residual‐P effectiveness where a total of 140, 280, and 560 kg P/ha were applied initially as one broadcast application or, in equal increments as banded applications, to the previous four crops. With a total application of 140 and 280 kg P/ha, the residual P from the banded applications gave greater corn yields and P uptake than the initial broadcast applications. At the 560 kg P/ha rate, where yields were nearly maximum, there were no differences in yield due to the application method. Soil test P levels indicated a considerable residual effect from the higher rates of broadcast P. Fractionation of soil P indicated a conversion with time of more soluble forms of P to less soluble forms. Estimates of P requirements from P. sorption curves suggested a residual efficiency of 40–60% of the previously broadcast fertilizer P. Although clayey Oxisols have a high P requirement for maximum yields, there is a considerable residual effect of fertilizer P which needs to be included in estimates of the efficiency of P fertilization.