Soil or land leveling, a process of adequation of land surface, is being practiced in many rice-growing farms in the state of Rio Grande do Sul, Brazil. This process produces profound changes in the morphological, physical, chemical, and biological properties of the soil. To study these changes, test areas were selected with homogeneous surfaces where Planosols occur and on which land leveling was performed for eight years, one year, and one month and with original soil, at São João do Polêsine. Soil morphology was described and soil samples collected at horizons and/or soil layers of leveled (cut and filled-in) profiles and original (unleveled soil) areas. In the areas of removal of (cut) material, significant changes were observed, namely higher clay content, low soil organic carbon and phosphorus, as well as higher exchangeable aluminum, mainly in areas of one year after leveling. The leveling process increased soil bulk density and reduced total porosity in the subsurface, due to the intense machinery traffic. The compaction of the surface layer was reduced by soil tillage and incorporation of rice crop residues. Total and DCB extracted iron and total aluminum of the subsurface layers of cut profiles were similar to the original Btg horizon. Soil wetting and drying cycles, originated by rice irrigation, affected the types of iron oxide, increasing oxides with low crystalinity.
Land leveling; soil morphology; iron oxides