To evaluate soyabean productivity on natural pasture fields, grown once with oats to produce grain and straw for soil cover, an experiment was conducted on a Typic Paleudult Soil in Eldorado do Sul, Rio Grande do Sul, Brazil. After mechanically harvesting oats, the straw was returned to plots in amounts of 0, 2, 3, 4, 5 and 6 mg/ha and were divided according to the furrow opening depth (0.06 and 0.12 m). The area was divided in 2, with and without irrigation. The volume of soil mobilized by the fertilizer furrow openers was 53% higher when the working depth reached 0.12 m compared to 0.06 m, but no difference due to the amount of cover crop residues was attained. Grain yield, crop biomass and root mass up to 0.15 cm depth did not differ with both soil working depth and crop residue cover. Irrigation increased grain yield and total biomass of soyabeans. Even without irrigation, soyabean productivity was higher than the Rio Grande do Sul State average, showing its suitability to be grown on native pastures under the no-till system.
