Residualidade do calcário e seus efeitos na produtividade de grãos em áreas sob sistema de plantio direto

Abstract

Surface liming in no-tillage systems (NTS), without mechanical incorporation, can effectively ameliorate soil acidity and increase the availability of exchangeable calcium (Ca²⁺) and magnesium (Mg²⁺). However, lime reaction and the downward movement of its reaction products are generally slower under surface application than under incorporation, particularly in soils with high buffering capacity. Uncertainty regarding appropriate lime rates and the frequency of reapplication may limit crop productivity. In addition, the need to reincorporate lime in soils managed under NTS remains uncertain, particularly in areas where soil fertility was not adequately built before the adoption of the system. Therefore, this study aimed to evaluate the effects of surface-applied lime rates, compared with an incorporated rate to a depth of 0.25 m, on soil chemical attributes and annual crop productivity under NTS, as well as to assess the efficiency and persistence of the residual effects of lime four years after application. The experiments were conducted independently from 2019 to 2024 in a randomized complete block design, with four replications, at four sites located in the municipalities of Carrancas (Site I), São João del-Rei (Site II), Ingaí (Site III), and Uberlândia (Site IV), representing soils with contrasting textures. The treatments consisted of five lime rates (0, 2, 4, 6, and 8 Mg ha⁻¹) applied to the soil surface, plus an additional treatment consisting of 8 Mg ha⁻¹ incorporated into the soil, resulting in a total of 24 plots of 200 m². Surface liming increased exchangeable and residual Ca²⁺ and Mg²⁺ contents, soil pH, and base saturation (V%), while decreasing H+Al contents. Four years after lime application, the residual effect of the amendment remained evident. Increases in soil pH and reductions in potential acidity in the 0.10–0.20 and 0.20–0.40 m layers indicated the downward movement of lime reaction products into the subsurface layers, accompanied by increases in exchangeable and residual Ca²⁺ and Mg²⁺ contents. The highest surface-applied lime rates produced greater corrective effects across the three evaluated soil depths, except at Site IV, which had the lowest clay content, highlighting the role of soil buffering capacity in determining liming efficiency. The incorporated rate was more effective than the lower surface-applied rates, particularly at Site IV, where incorporation resulted in marked increases in all evaluated soil chemical attributes. These results demonstrate that liming efficiency is strongly influenced by soil texture and buffering capacity and that the effects of liming can persist for several years, with residual lime remaining in the soil. Although incorporation promotes faster and more uniform amelioration throughout the soil profile, surface application can also provide substantial improvements when an adequate lime rate is applied. During the final two years of cultivation, beginning three years after lime application, increases in crop productivity in response to surface-applied lime rates were observed at Sites II and IV, particularly during the 2024/24 growing season, which was characterized by lower water availability. Except at Site I, cumulative productivity over the final two growing seasons increased with increasing surface-applied lime rates, whereas lime incorporation did not result in significant increases in crop productivity.