ATRIBUTOS QUÍMICOS DE UM LATOSSOLO E OMPORTAMENTO DO TRIGO E DA SOJA NO SISTEMA PLANTIO DIRETO INFLUENCIADOS PELA APLICAÇÃO E REAPLICAÇÃO DE GESSO AGRÍCOLA PONTA GROSSA – PR

Abstract

Gypsum application provides chemical changes on soil that can improve crop yield. This study was carried out to investigate the gypsum application and reapplication effects on soil chemical attributes, mineral nutrition and wheat and soybean grain yields under a no-till system. A field experiment was established in 1998 on a dystrophic clayey Rhodic Hapludox, in Ponta Grossa, Parana State, Brazil. A randomized complet block design was used, with three replications, in a split plot experiment. Gypsum was surface-applied at rates of 0, 3, 6, and 9 t ha-1 in 1998 (main plots) and two rates of gypsum at 0 and 6 t ha-1 were reapplied on the soil surface in 2004 (subplots). Mineral nutrition and graind yields of wheat (cv. OR 1), conventional soybean (cv. BRS 154) and tansgenic soybean (cv. CD 214 RR) were evalueted in the period of 2005-2007. Gypsum rates applied in 1998 presented long-term effects, mainly increasing the S-SO4 2- content and raising wheat dry mass. Grain yields of wheat, conventional soybean and transgenic soybean were not influenced by gypsum applied in 1998. Gypsum reaplication in 2004 increased the exchangeable Ca2+ and S-SO4 2- contents in all soil profile (0-60 cm), increased Ca2+/Mg2+ ratio, mainly on topsoil (0-5 and 5-10 cm), decreased Al3+ saturation on subsoil (20-40 and 40-60 cm) and provided leaching of exchangeable Mg2+ from topsoil (0-5 cm). Gypsum reapplication increased the concentrations of K, Ca, and S in wheat leaves and the Ca concentration in conventional soybean (cv. BRS 154) leaves. Grain yields of wheat and transgenic soybean (cv. CD 214 RR) were increased by gypsum reapplication. The increment in wheat yield with gypsum reapplication was related to increase in exchangeable Ca2+, Ca2+/Mg2+ ratio, and S-SO4 2- content, and also to decrease in exchangeable Al3+ and Al3+ saturation in the subsoil layers. Transgenic soybean yield (CD 214 RR) was higher with gypsum reapplication due to increase in the S-SO4 2- level in the soil, showing that the transgenic genotype (CD 214 RR) has probably demand higher in sulfur than the conventional genotype (cv. BRS 154). Gypsum reapplication at 6 t ha-1 in 2004 increased the cumulative grain yield of wheat and soybean in 7% in the period from 2005 through 2007, indicating technical viability on soil with low acidity in the subsurface layers.