The objective of this work was to evaluate the effect of soil winter covers and soil mechanical loosening on soybean and corn yield, in no-tillage system. Two experiments were carried out in Rio Grande do Sul state, Brazil, in a compacted Argissolo Vermelho (Haplic Acrisol), in the 2005/2006 and 2006/2007 crop seasons. The first experiment was carried out in a complete block design, with a split plot arrangement. The treatments were two theoretical working depths of a driller chisel-type furrow opener (0.06 and 0.12 m, split plot), and three soil winter covers (main plot): fallow, black oat ( Avena strigosa), and black oat+common vetch ( Vicia sativa). In 2006, the soil cover black oat+common vetch was replaced by oilseed radish ( Raphanus sativus). In the second experiment, in a complete block design, the soil was chiseled and treatments consisted of black oat or oilseed radish as winter cover crops. Cover crops reduced soil superficial (0-0,06 m) compaction compared to fallow and, in the 2005/2006-crop season, under low water availability, provided higher soybean and corn yields. In the 2006/2007-crop season, when water availability was higher, the same did not happen. Increasing working depths of the chisel-type furrow opener did not affect soybean or corn yields. Soil chiseling reduced soybean and corn yields in comparison to the continuous no-tillage system.
