Residual effect of potassium fertilization applied to soybean in three different Oxisols

Abstract

Sunflower and corn are two new crop options to be considered in the soybean-wheat double-cropping system. However, there is little information on mineral nutrition for these two crops. With the objective of studying the residual effect of potassium fertilization applied for soybean, on the K-content of sunflower and corn leaves and their yield, three experiments were run on three Oxisols: Latossolo Roxo distrófico (LRd), Latossolo Roxo álico (LRa) and Latossolo Roxo eutrófico (LRe). All these three soils had the exchangeable-K depleted by soybean-wheat double cropping for ten years. In the first five years they were K-fertilized by zero, 40, 80, 120, 160 and 200 kg/ha/year of K₂O, and in the next five years no K fertilizer was applied. It was concluded that K absorption by plants will be restricted and the leaf content will be less than 18.8 g kg^-1 of K. This will restrain sunflower yield in Oxisol soils with less than 0.12 cmol_cdm^-3. For corn, K-leaf content less than 15.5 g kg^-1 of K decreases yield. Thus, in order to obtain maximum corn yield, the avaliable K (Mehlich-1) should be higher than 0.15 cmol_c dm^-3 and the K-leaf content higher than 15.5 g kg^-1