Changes in chemical soil characteristics and soybean response to lime and gypsum applications in a no-tillage system

There has been an increasing interest to search alternatives for the establishment of crops under no-tillage systems in the southern region of Brazil, opening up new areas without soil disturbance. A field trial was carried out, on a dystrophic Clay Rhodic Hapludox in Ponta Grossa, Parana State, Brazil, from 1998 to 2001, with the aim to evaluate changes in chemical soil characteristics, as well as the soybean response to lime and gypsum applications in a no-tillage system. A completely randomized block design with three replications in a split-plot experiment was used. The main plots received dolomitic limestone treatments (no lime, total rate of 4.5 t ha(-1) of lime, 113 of this dosage during three years, as surface application and incorporated into the soil) and the subplots, the gypsum rates (0, 3, 6, and 9 t ha(-1)). Liming, whether surface applied or incorporated into the soil, provided a more accentuated soil acidity correction in the superficial layer (0-5 cm), but there was a stronger reaction in the 5-10 and 10-20 cm layers when lime was incorporated into the soil. The beneficial effects of lime for subsoil acidity correction were not very pronounced and more evident where lime was incorporated. Gypsum improved the subsoil, increasing the pH (CaCl(2) 0.01 mol L(-1)), Ca, and S-SO(4)(2-) concentrations, P concentrations in the superficial soil layer (0-5 cm) and in soybean leaves, and decreased Mg concentrations in the soil and soybean leaves. Results showed no soybean response, in three years, to lime and gypsum treatments. It was concluded that gypsum, whether applied as superficial or incorporated liming, did not present an interesting strategy for the installation of soybean crop in a no-tillage system, since no improvement in grain yields could be observed.