Improvement in Chemical Attributes of Oxisol Subsoil and Crop Yields under No-Till

The natural chemical qualities of the subsoil of Oxisols often restrict root growth, water use efficiency, and crop yield. The practice of continuous no-till farming creates a fertile topsoil but generally does not affect the subsoil. This study aimed to evaluate the effectiveness of gypsum in improving the chemical attributes of the subsoil and increasing crop yields. To this end, the experiment was conducted at two sites in distrophic Red Oxisols located in southern Brazil. The experimental design was a randomized complete block with three replications. Treatments consisted of broadcast gypsum rates of 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.5 Mg ha(-1). Soil samples were collected from the root zone at the beginning of the experiment and after six and 22 mo to evaluate soil pH and extractable P, K+, Ca2+, Mg2+, Al3+, and SO4-S concentrations. After 6 mo of gypsum application, an increase in exchangeable bases associated with a decrease in Al3+ concentrations in the subsoil was noted, and this improvement was intensified further by 22 mo. An increase in crop yields was related to the increase in base saturation and Ca2+ saturation and a decrease in Al3+ saturation in the 25- to 40-cm soil depth. Surface application of gypsum was an effective method of improving the chemical quality of the rooting zone in Oxisols under continuous no-till farming and resulted in a higher impact on corn (Zea mays L.) grain yield than soybean [Glycine max (L.) Merr.] yield.