Compactação, cobertura do solo e produtividade de soja em terras baixas

Abstract

Soil cultivation in the lowlands has been gaining ground in the Western Frontier of Rio Grande do Sul. However, naturally these soils have high density, and consequently problems of surface compaction affecting plant growth. The study evaluated the effect of straw on the soil surface on physical properties, water retention and soybean yield in non - composting systems. The experimental design was completely randomized with seven treatments and four replications. The treatments were: 1) Winter fallow without compaction (PO); 2) Winter fallow + compaction (POC); 3) No-tillage oat planting (PD), with cut of plants at 0.03 m height and total removal of the surface straw at the end of the cycle + compaction (0PC); 4) Seeding of notillage oats with cut of plants at 0,03m height removal of half of the surface straw at the end of the cycle + compaction (0,5PC); 5) No-till oat planting, with cut of plants at 0.03m height and soil surface spreading at the end of cycle + compaction (1PC); 6) No-till oat planting, with cut of plants at 0,03 m of height and spreading on the soil surface at the end of the cycle + the straw withdrawn from the treatment 3, the treatment 6 being equivalent to twice the amount of straw on the surface of the soil + compaction (2PC); 7) No-till oat planting, with plant cut at 0.03m height and spreading on the soil surface at the end of cycle and without compaction (1P). In the R5 phenological stage, four samples were taken by insertion between the rows, with cylinders 3 cm high and 5 cm in diameter to evaluate soil density and total porosity, macro and microporosity, and water retention at potentials of -0.06; -0.1; -0.3; -0.6; -1,0 and -1.5 MPa, in the layers of 0.05-0.10 and 0.15-0.20 m depth. The physical properties of the soil were not altered by the different treatments in the depths of 0.05-0.10 and 0.15-0.20 m. The water retention was lower in the POC treatment at potentials -0.3, -1,0 and -1.5 MPa. Soil cover provides higher soybean yield in 1PC, 2PC and 1P treatments.