Crop livestock integration systems (CLIS) involving pastures of Brachiaria brizantha in autumn/winter and soybeans in summer have been considered an option to increase and diversify crop production and improve no-tillage system. This work aimed to evaluate the effect of grass desiccation timings or cattle grazing pressures on soil physical attributes and soybean yields in a crop-livestock integration system. The experiment was carried out on a dark red Latosol (Rhodic Eutrudox, US Soil Taxonomy) in southern Brazil. In the major plots, grazing pressures of 6.9, 9.4, and 16.5 animal unities per hectare were applied during 19 days to a pasture of Brachiaria brizantha cv. 'Xaraes', which phytomass was desiccated 30 days before soybean sowing (DBS). Ungrazed plots were desiccated 30, 44 and 52 DBS. Remaining phytomass of the pasture; soil bulk density, porosity and soil resistance to penetration; and yield of soybean cultivars 'BRS 294RR' and 'BRS 255RR' (sowed in subplots), were determined. Changes in soil physical attributes by animal trampling were concentrated on topsoil layer (0.0-0.05m), and soil compaction level was increased by the highest grazing pressure down the 0.2-0.3 layer. The yield of soybean cv. 'BRS 294RR' was increased with rising grazing pressures, whereas the yield of soybean cv. 'BRS 255RR' was not affected, showing that soybean genotypes had different responses to soil compaction level and, mainly, to remaining phytomass of pasture. In CLIS with high production of B. brizantha dry mass, soybean yields are closely associated to time interval between grass desiccation and soybean planting.
Glycine max; Brachiaria brizantha; grazing management; soil compaction; no-tillage system
