Modern High-Yielding Maize, Wheat and Soybean Cultivars in Response to Gypsum and Lime Application on No-Till Oxisol
ABSTRACT Modern maize, wheat, and soybean cultivars are usually characterized by a short cycle, high shoot-root ratio, and high responsiveness to nutrient input. Continuous no-tillage management (NTS) frequently leads to a steep gradient in soil chemical quality with depth, thus decreasing yield under conditions of acid subsoil and water stress. This study aimed to evaluate the effect of gypsum, applied separately or in combination with lime, on the yield of cultivars used in the state of Rio Grande do Sul, Brazil. The study consisted of four experiments conducted on a typic Hapludox under NTS. The experiment was arranged in a randomized block design with three replications. Experiments I and II were carried out on soils with a satisfactory chemical soil quality and tested treatments of gypsum applications ranging from 0.0 to 6.5 Mg ha-1. The other experiments were carried out on acid soil (experiment III) and a soil with an abrupt drop in chemical quality (experiment IV). Experiment III was arranged in a split plot design, where plots corresponded to gypsum rates between 0.0 and 5.0 Mg ha-1, and subplots to two lime rates (0.0 and 2.0 Mg ha-1). Experiment IV was conducted in a split plot design, with plots consisting of gypsum rates from 0.0 to 6.0 Mg ha-1 and subplots of lime rates from 0.0 to 4.8 Mg ha-1. Of a set of 17 harvests investigated during the experimental period, 82 % responded with yield increases to gypsum and lime inputs. The gypsum rate that induced the highest grain yield was high (4.7 Mg ha-1) and similarly, the maximum technical efficiency of lime was higher than the currently recommended. Furthermore, the combined application of lime and gypsum increased yield. There was a correlation between grain yield with the chemical quality of the soil layer 0.25-0.40 m in experiment I, 0.00-0.40 m in experiment II, and the 0.00-0.25 m in experiment IV. Only in experiment III, where the surface layer was acidic, the diagnostic layer usually sampled (0.00-0.10 m) was correlated with grain yield. Therefore, the use of the 0.00-0.25 m soil layer with critical base saturation values of 65 % and maximum Al saturation of 5 % could improve the current recommendations for soil correction. To exploit the yield potential of modern grain cultivars on dystrophic Oxisol, the formation of a thicker layer with high chemical quality is an efficient strategy.