Effect of soil compaction in root development and in soybean yield

In compacted soils, changes in the distribution of plant root system occur in depth. The objective of this study was to evaluate the compaction effect in soybean root development and yield in an Oxisol. The treatments were 0, 1, 2, 4 and 6 passed of a 11 Mg tractor, side, by side, on soil surface. The experimental design was a completely randomized, with four replications. In December, 2002, soybean (Glycine max cv. Embrapa 48) was sown, and after that, the samples were collected in layers of 0.02-0.05, 0.07-0.10 and 0.15-0.18 m, for physical determinations. In R6 stadium, samples of 0.10 m in line x 0.20 m between lines, in layers of 0.0-0.05, 0.05-0.10,0.10-0.15 and 0.15-0.20 in were collected. Soybean yield was evaluated in plots of 3.6 m(2). The increase in compaction increased the root density and the root dry matter in layer of 0.0-0.05 m and caused linear decrease in the most compacted layers of 0.05-0.10 and 0.10-0.15 m. From the decrease of 18% of root density, in resistance to penetration of 0.85 MPa, in the depth of 0.05-0.15 m, there was reduction in soybean yield. Soil compaction promoted modifications in the distribution of the soybean root system.