Cm. Borkert et al., FERTILIZATION RESPONSE AND POTASSIUM AVAI LABILITY FOR SOYBEAN IN OXISOL, Pesquisa agropecuaria brasileira, 32(10), 1997, pp. 1009-1022
The soil, when intensively cultivated with soybean-wheat double-croppi
ng system during several growing seasons, has the available K (fixed a
nd specifically adsorbed K) reserves depleted after some years of crop
ping. This causes soil K deficiency for crops and yield reduction. The
objective of this work was to study the soybean response to K fertili
zation, and the residual effect on soybean yields, on leaf and soil K
content. The experiment was run with soybean during the growing season
s 1983/84 through 1992/93 in a 'Latossolo Roxo eutrofico' (Eutrorthox)
in Londrina, Parana State, Brazil. In the first five years rates of z
ero, 40, 80, 120, 160 and 200 kg/ha/year of K2O were applied. After te
n years of experimentation it was concluded that in the 'Latossolos Ro
xos eutroficos' of high fertility, even with high K availability the s
oybean cannot be cultivated for more than two years without K fertiliz
ation, with high probability to have limitations to obtain maximum yie
lds. The K maintenance of 80 kg/ha/year of K2O is not enough and in fi
ve years of double-cropping almost depleted the soil-K. The fertilizat
ion should be at least 120 kg/ha of K2O for soybean and 160 kg/ha/year
of K2O for the soybean-wheat double-cropping system to keep top yield
s of 3,000 to 3,500 kg/ha. Soybean high yields, over 3,000 kg/ha, were
associated with K in the leaf tissue higher than 17.1 g/kg.