Cm. Borkert et al., RESIDUAL EFFECT OF POTASSIUM FERTILIZATIO N APPLIED TO SOYBEAN IN 3 DIFFERENT OXISOLS, Pesquisa agropecuaria brasileira, 32(12), 1997, pp. 1227-1234
Sunflower and corn are two new crop options to be considered in the so
ybean-wheat double-cropping system. However, there is little informati
on on mineral nutrition for these two crops. With the objective of stu
dying the residual effect of potassium fertilization applied for soybe
an, on the K-content of sunflower and corn leaves and their yield, thr
ee experiments were run on three Oxisols: Latossolo Roxo distrofico (L
Rd), Latossolo Roxo alico (LRa) and Latossolo Roxo eutrofico (LRe). Al
l these three soils had the exchangeable-K depleted by soybean-wheat d
ouble cropping for ten years. In the first five years they were K-fert
ilized 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 l
ess than 18.8 g kg(-1) of K. This will restrain sunflower yield in Oxi
sol soils with less than 0.12 cmol(c) dm(-3). For corn, K-leaf content
less than 15.5 g kg(-1) of K decreases yield. Thus, in order to obtai
n maximum corn yield, the available K (Mehlich-1) should be higher tha
n 0.15 cmol(c) dm(-3) and the K-leaf content higher than 15.5 g kg(-1)
.