João de Andrade Bonetti
Abstract:
Modern agriculture requires adoption of cropping systems that maintain soil quality. Thus, studies on soil science are directed to the identification of these systems. The crop-livestock integration in no-till is in this context and its study, regarding the effects on the soil, has indicated high potential as a conservation system. The system can be inserted in several regions, using adapted animals and fodder. Its sustainability is obtained due to benefits such as extensive pasture recovery and low production capacity, as well as physical and chemical recovery in areas of grain production. This is due to greater aggregate stability, increased porosity, macro and microporosity, reduced erosion and soil loss by runoff, maintenance of soil moisture, increased water infiltration and large straw input over the soil. These benefits are important, especially in Cerrado soils where low clay activity and low cation exchange capacity are observed. This makes these soils dependent on the addition of organic matter, a fact provided by brachiaria both on surface and subsurface. However, to obtain these benefits of crop-livestock integration, studies are still needed to identify appropriate management, especially regarding the replacement of organic matter for the maintenance of no-tillage, effects on soil structure and yields of grain and forage crops. The aim of this study was to evaluate the physical attributes of the soil in post-soybean and post-grazing areas under different grazing intensities, the effect of animal trampling in depth, soybean and brachiaria yield and to analyze the evolution of the attributes. soil physics after four years of cultivation, by comparing sampling times and grazing intensity in a Cerrado ditroferric Red Latosol. The experiment was installed in the 2008/09 crop and extended until the 2011/12 crop. The system consists of soybean in summer (October to February) and second crop with brachiaria (March to September) and subsequent grazing. The xv treatments were composed by pasture height management at 25, 35 and 45 cm and no grazing area, arranged in a randomized block design. Animal trampling provided changes only at depth from 0 to 5 for the total post-grazing porosity, not altering soil density, macro and microporosity. It was verified increased of the weighted average diameter in the 0 to 5 cm layer after four years of cultivation and with greater aggregation in the grazed areas. The higher grazing intensity provided greater mechanical resistance to penetration in the 0 to 5 cm layer, but with values below those considered critical to plant development. However, there were no significant changes between the studied periods. It can also be observed that after four years of installation of the experiment the soil structure returned to values close to the initial state of extensive pasture for 20 years, with no reduction in soybean yield in 2011/2012, the last crop analyzed.
