Manejos do solo e uso de calcário para cultivo de soja em planossolo

Abstract

In Rio Grande do Sul State, flooded rice monoculture in lowland areas is being difficulted due to the increase of production costs, mainly by weeds control and yield stagnation. Crop rotation is a strategy to be adopted in this environment. Soybean is a crop that can be managed in rotation with irrigated rice. However, these areas are characterized by poor drainage, low hydraulic conductivity and compacted layer near to the soil subsurface, factors considered limiting to the development of rainfed plants, with direct repercussions on yield reduction. These stresses can significantly reduce the growth and development of soybean plants, limited by important physiological processes, such as, photosynthesis and biological nitrogen fixation. In view of the above, the objective of this work was to evaluate the influence of different soil management and liming on soil physical attributes, agronomic and physiological characteristics and soybean grain yield in lowland areas. The experiment was conducted in the 2017/18 and 2018/19 growing seasons, at the experimental field of the Irrigated Rice Research Group (GPai) of the Federal University of Santa Maria (UFSM), in Santa Maria-RS. The experimental design was randomized complete block in a 4 × 2 factorial with four replications. Factor A consisted of tillage systems: (A1) no-tillage; (A2) spring disc harrowing with 0.08 m depth (2017/18 harvest) and harrow plow with 0.15 m depth (2018/19 harvest); (A3) deep tillage with 0.30 m depth and (A4) double deep tillage with 0.30 m depth; and factor D, limestone use or not. According with the main results obtained, can be observed that the benefits of limestone use in lowland areas, with presence of subsurface compacted layer, remain restricted to the depth of 0-0.10 m, regardless of spring disc harrowing, harrow plow or deep tillage use, 120 days after the application of the concealer. Deep tillage management increased macroporosity and reduced soil density and mechanical penetration resistance in the 0-0.30 m depth layer. Deep tillage and double deep tillage, together with the plow harrow, resulted in higher root system development, nodule dry mass, shoot dry mass, plant height and macronutrient content in leaf tissue and higher grain yield in lowland areas, due to the smaller restriction of photosynthetic rate.