This study had as objective to evaluate the effects of crops succession and rotation on physical properties and crops yield on an Oxisol (clayey Haplortox) under no tillage system, in Rio Grande do Sul State, Brazil. The treatments included four cropping sequences, used from 1998 to 2001: 1) succession wheat / soybean, 2) rotation corn / oat / corn+ Cajanus cajan L. Millsp / wheat / soybean / wheat, 3) rotation Cajanus cajan L. Millsp / wheat / soybean / wheat / soybean / oat, and 4) rotation Crotalaria juncea L. / wheat / soybean / oat / corn / wheat. In October of 2000 and 2001, soil samples were collected to determine physical properties. In all years, the crops yield was measured. The Oxisol cultivated under no-tillage had a high compaction degree, with soil bulk density greater and macroporosity smaller than the critical limit for clay texture. The largest limitations were observed below the layer of 0 to 0,03m, because in the uppermost layer soil mobilization by successive operations of fertilization and sowing increases soil porosity and reduces soil density. Thus, greater volume of pores is observed between soil saturation and field capacity, responsible for soil aeration, and between field capacity and wilting point, responsible for storage of plant available water. The use of cover crops once every three years was not efficient to reduce soil compaction. The yield of the subsequent crops was influenced positively in the rotation with Crotalaria juncea, while the other cropping systems did not differ from crop succession.
soil structure; compaction; water retention curve
