Soybean yield and quality as a function of lime and gypsum applications

Effects of lime and gypsum applications on the quality of soybeans grown under no-till (NT) are not well defined yet. A field trial established in 1998 on a dystrophic clayey Rhodic Hapludox, at Ponta Grossa, State of Parana, Brazil, evaluated grain yield and soybean quality based on oil, protein and nutrient content, after lime and gypsum applications under NT, in a randomized complete block design (n = 3), split-plot experiment. In the main plots, the treatments with dolomitic lime were: control (no lime), split application of lime on the surface (three yearly applications of 1.5 Mg ha(-1)), surface lime (4.5 Mg h(-1)), and incorporated lime (4.5 Mg ha(-1)). Subplots received four different rates of gypsum: 0, 3, 6, and 9 Mg ha(-1). The soybean crop was evaluated in the agricultural years of 2002-2003 and 2003-2004. After 58 months, the correction of acidity through surface liming, with full or split rates, was more pronounced in the top layer (0-0.05 m) and there was greater reaction at the depths of 0.05-0.10 and 0.10-0.20 m when lime was incorporated. Surface or incorporated liming had no effect on grain yield, soybean oil and protein content. Gypsum improved chemical subsoil conditions, raising pH (0.01 mol L-1 CaCl2) as well as Ca2+ and S-SO42- contents; it also caused exchangeable Mg2+ leaching in the soil profile. The application of gypsum did not affect grain yield, yet it improved soybean quality through an increase in protein and S contents, in 2003-2004, and in grain P, K and Ca, in the two cropping years. The use of gypsum in NT soybeans can be especially important for fields of seeds production.