Despite the efficiency of no-tillage in improving soil and water conservation, the machinery traffic and absence of soil tillage can lead to surface compaction in clayey soils. The Least Limiting Water Range (LLWR) expresses the effects of management systems on the improvement or degradation of soil physical quality. The objective of this study was to quantify LLWR to discriminate the effects of management systems under no-tillage on soil physical quality. The treatments were crop succession under no-tillage, crop rotation under no-tillage and crop rotation under no-tillage plus chiseling. In two different seasons, October 2002, after the winter crop (wheat) and April 2003, after the summer crop (soybean), 44 undisturbed samples were collected in each treatment. The samples were used to determine the soil water retention and soil resistance curve, bulk density, LLWR and critical bulk density. The soil penetration resistance determined the lower limit of LLWR for all treatments and the LLWR declined as the soil bulk density increased. The critical soil bulk density was not influenced by management systems. The temporal variation of LLWR was dependent on soil bulk density variation. The greater soil water retention values at high potentials in the no-tillage with crop rotation treatment led to temporary higher LLWR values.
soil penetration resistance; soil management; soil bulk density; crop rotation; soil structure
