Estratégias de manejo físico e químico para melhoria dos atributos da camada de enraizamento profunda em sistema plantio direto de qualidade

Abstract

The no-till system brought any benefits to crop systems, as the reduction of the soil erosion and of costs of the production, increase of the water retention, higher accumulation of soil organic matter, increase of the microbial population in the soil, among others. However, soils managed under long-term no-till, mainly the clay soils, tend to present physical and chemical limitations in function of the absence of soil tillage, of the superficial application of the correctives and fertilizers and of the intensive traffic of machines and implements increasingly higher and with more height. The chemical and physical conditions of the soil profile affects the growth, development and distribution of the root system of the plants in the soil and, consequently, the yield of the crops. Thus, the aim of this study was to evaluate the effects of the chemical and physical improvements in the soil properties, the rooting and seed yield of the soybean in the absence and in the presence of the water deficit. The experiment was realized in in the municipality of Dois Irmãos das Missões in the Rio Grande do Sul, in two crop seasons (2016/17 and 2017/18) and you experimental design was a randomized block design with three replications. The treatments were constituted by the Test. (control), T1 (subsoiling with 70 cm spacing), T2 (chiseling with 50 cm spacing), T3 (subsoiling with 70 cm spacing + deep application of Ca and Mg oxide with 70 cm spacing), T4 (chiseling with 50 cm spacing + surface application of Ca and Mg oxide), T5 (surface application of Ca and Mg oxide), T6 (surface application of limestone + gypsum), T7 (surface application of Ca and Mg oxide + limestone + gypsum) and T8 (subsoiling with 35 cm spacing + deep application of Ca and Mg oxide with 70 cm spacing). The soil samplings was realized 6 and 18 months after the application of the treatments and were stratified in the soil layers of 0.00-0.10, 0.10-0.20, 0.20- 0.40, 0.40-0.60, 0.60-0.80 and 0.80-1.00 m. Were determined the pH, aluminum saturation, calcium, magnesium and sulfur contents, the cation exchange capacity and the basis saturation. The physical attribute evaluated was the mechanical penetration resistance of the soil, that was performed from 0 untill 60 cm depth. The root sampling was performed in the soybean full flowering. The simulation of water deficit was realized with the installation of restriction chambers during the soybean reproductive stage for approximately 30 days, and restricted 100% of the incident precipitation. The physical improvement of the line and the interline (subsoiling with spacing of 35 cm) associated to deep application of Ca and Mg oxide (with spacing of 70 cm) increase the pH values and reduced the aluminum saturation of the soil profile, beyond improve the root distribution in the soil profile and increase the volume and length of the soybean roots. This association was efficient to mitigate the yield losses in water deficit situations, after 18 months the application