Abstract

Long-term no-till with shallow fertilizer input results in a chemical enriched topsoil but has minor effect of subsoil. The sub-optimal use of water and mobile nutrients stored in the subsoil layers is a frequent limiting factor to crop grain yield in tropical acid soils. This study aim assesses the corn and soybean grain yield response to gypsum combined with lime surface input as a tool for subsoil chemical quality improving. A Brazilian distrophic Oxisol located in Carazinho (RS State, BR) managed under continuous no-till with characteristics of good chemical soil quality in the topsoil and with a poor condition in the subsoil was select for this study. The experiment design was a randomized block with three replications. The following chemical treatments were broadcast on soil surface as followS: (a) control; (b) 2.5 Mg ha^-1 of gypsum + 2.0 Mg ha^-1 of dolomitic lime; and (c) 5.0 Mg ha^-1 of gypsum + 2.0 Mg ha^-1 of lime. Both chemical inputs were applied simultaneously, the rates were determined based on lime requirement according to South state fertilizer recommendation and gypsum according to Midwest (Savanna) recommendation. The soil samples were stratified in the 0.00 to 0.60 m soil layer with four sampling times at 0, 6, 22 and 34 months after experiment establishment. An increase in the calcium and magnesium soil contents, as well as soil base saturation, and a decrease in aluminum content, was verified in subsoil layers (0.15 to 0.25 m and 0.25 to 0.40 m) just after six months of chemicals application. These subsoil ameliorate effect was intensified with the conducting time of the experiment notedly at 22 months after chemical application. Moreover, it was found crop grain yield increments statistically significant ranging of 9 to 16%. The gypsum combined with lime was an effective alternative for improving vertically nutrient content of the Oxisol’s decreasing the abrupt transition in chemical quality of topsoil and subsoil helping to the maintenance of competitive grain yield under non-disturbed long-term no-till.

Key words: Gypsum, subsoil acidity, soil fertility, calcium, sulfate.