Changes in composition and functional soil properties in long-term no-till integrated crop-livestock system

Abstract

Integrated Crop-Livestock Systems (ICLS) are an important alternative to winter fallow and increase the sustainability of production systems, by combining agricultural with livestock production. The hypothesis of this study was that load applied by animals in moderate grazing does not promote further soil structural degradation. The objective of this study was to demonstrate changes in soil structure, mechanical behavior, and water and air permeability caused by different intensities of grazing in ICLS. The experiment consisted of a 15-years old ICLS, managed with soybean Glycine max in the summer and black oat Avena strigosa + ryegrass Lolium multiflorum in winter with continuous grazing by beef cattle. The treatments consisted of different grazing intensities determined by sward height, namely 0.10 m (heavy grazing) and 0.30 m (moderate grazing), and a control (without grazing), in an experimental design of randomized blocks with three replications. Undisturbed soil samples were collected in core samplers in the 0–0.05, 0.05–0.10, and 0.10–0.20 m soil layers, in two evaluation times: (i) post soybean (immediately after soybean harvest, and before pasture sowing or animal grazing), and (ii) after grazing (immediately after withdrawing the animals from the area and before soybean sowing), respectively in April and November 2015. Soil bulk density, macroporosity, microporosity, air permeability, saturated hydraulic conductivity, precompression stress, compressibility coefficient, decompression coefficient, and cyclic compressibility index were determined. The results indicate grazing increases the compaction state of the soil surface mainly in the post grazing period by the direct effect of animal treading. However, there is a mitigation effect during the soybean cycle, evidencing the soil's regeneration capacity in ICLS, provided by intense biological activity, wetting-drying cycles, and decomposition of pasture roots that regenerate soil structure. Moderate grazing is a better option than intense grazing, but without soil improvements when compared to the non-grazed system.