Traffic-induced compaction of an Oxisol and its relation with growth and yield of common bean and wheat

Soil compaction is a limiting factor to increase yields and to develop long-term no-till, especially in clayey soils. The objective of this study was to evaluate the effect of compaction levels on soil bulk density, porosity and penetration resistance, as well as the consequences on root growth, leaf area index and yield of common bean and wheat in crop succession. The treatments were: NT-continuous no-till for six years; NTc-NT with additional compaction; Chi - chisel plow on NT. The experimental design was completely randomized with three replications. The highest bulk density was found in the in the 0.05-0.15 m layer of the soil under NTc, with values over 1.5 Mg m(-3). Soil resistance to penetration exceeded 2 MPa in the driest periods, with moisture (theta) < 0.28 m(3) m(-3), and highest values were observed at the soil surface (0.05 to 0. 15 m) for NTc and NT Root growth was most affected at 0,1 m depth under NTc, which resulted in a restricted development of the leaf area and shorter bean plants. Root growth was less restricted and the leaf area and plant height were greater under NT and Chi. Common bean yield in NTc was 17% lower than under NT. Chisel plow did not affect the common bean yield significantly. In wheat, yields tended to be lower in NTc and Chi than in NT. Chisel plow was therefore not necessary to alleviate soil compaction in this Oxisol under no-tillage for six years.