The physical quality of a Typic Hapludalf in a no-tillage system was evaluated after the use of cover crops, and the critical limit of bulk density was measured. In autumn/winter of 1999/00 and 2000/01, the site was cultivated with black oats ( Avena strigosa) [ Avena nuda] with vetch ( Vicia sativa) and in 2001/02, with forage turnip ( Raphanus sativus). Corn ( Zea mays) was sown in summer and at the end of the cycle, four summer cover crops ( Crotalaria juncea, Cajanus cajan, Stilozobium cinereum and Canavalia ensiformis) were sown compared to fallow soil. Soil bulk density and penetration resistance were measured. The rooting system was evaluated by a root profile method during the cycle of forage turnip, corn and summer cover crops. The soil bulk density was increased by no-tillage to levels considered critical for plant growth. The root growth of all crops used in the rotations suffered some degree of restriction. There was no difference among the species in their root growth potential in the compacted soil. The root growth of the cover crop was normal up to a bulk density of 1.75 Mg/m 3, while values between 1.75 and 1.85 Mg/m 3 were restrictive, with visible deformation of the root morphology. These deformations were more pronounced when bulk density was greater than 1.85 Mg/m 3, with increased root thickening, deviations in the vertical root growth direction and concentration of roots in the topmost soil layer. The evaluated species can be used in compacted soils, but at soil bulk density >1.85 Mg/m 3, soil mobilization through mechanical methods may be necessary to alleviate the effects on root and plant growth.
