Tillage is one of the most important components of soil management in the process of crop production, normally used to create a favorable environment for sowing, seed germination and plant development. In addition, it is mainly determinant for the or surface soil physical conditions that will ultimately determine the erosion and the effectiveness of runoff reduction of the various soil management systems used to establish a given crop, in a given place. Considering these aspects, a field study under natural rainfall erosion was conducted in Lages, in the Southern upland region of the State of Santa Catarina, Brazil, between November, 2002, and October, 2005. The main objective of the study was to quantify soil and water losses caused by water-rainfall erosion through wheat (Triticum aestivum, L.) and soybean (Glycine max, L) crop cycles, using conventional (one plowing and two diskings), reduced (one chiseling and one disking), and no tillage (direct seeding), to determine the erosion and effectiveness of runoff reduction of these forms of soil use and management. The experiment was planted on a silt clay loam Inceptisol, with 0.102 m m-1 mean slope steepness. Plant and water-rainfall erosion parameters were evaluated in five crop stages, defined on the basis of percent of soil cover per plant canopy. The total rainfall amount was about the same (approximately 650 mm) in both crop cycles, with some variation in distribution, but with a greater concentration in the period from the middle to the end of the wheat cycle and the initial period of soybean. The rain erosivity pattern was similar, but with clearly different absolute values in each crop cycle (1,545 MJ mm ha-1 h-1 in wheat and 2,573 MJ mm ha-1 h-1 in soybean). The determined mean annual value of the soil erodibility index (factor K in the USLE or RUSLE erosion prediction model) was equal to 0.018 Mg ha h ha-1 MJ-1 mm-1. The mean annual losses of soil and water were generally relatively small in all situations studied, although soil losses were greater in wheat and water losses higher in soybean. Both loss types decreased in the order conventional-, reduced-, and no-tillage. The soil loss was proportionally much more reduced by tillage than by water loss. The provisionally determined mean annual values of the C factor - soil cover and management in USLE or in RUSLE erosion prediction model for the wheat-soybean crop sequence in the experimental climatic conditions were 0.23 when using conventional tillage, 0.06 for reduced tillage, and 0.023 for no-tillage or direct seeding.
rain erosivity; soil erodibility; soil tillage; wheat crop; soybean crop; factor C - soil cover and management; USLE; RUSLE
