LOSS OF WATER AND NUTRIENTS IN DIFFERENT SOIL TILLAGE SYSTEMS SUBJECTED TO NATURAL RAINFALL IN THE STATE OF MATO GROSSO, BRAZIL

The aim of this study was to evaluate the loss of water and nutrients by laminar runoff in different soil tillage systems subjected to natural rainfall. Five experimental plots were established for the cultivation of cotton in the city of Campo Verde - MT, with the following treatments: CTDP = conventional soil tillage and planting of the cotton in the direction of the slope; CTCP = conventional tillage and contour planting; CP = tillage of soil with a disk harrow and a leveling harrow, followed by contour planting; CoP = tillage by two passes of a leveling harrow followed by contour planting; MTCP = minimum tillage with contour planting. The losses of water by laminar runoff in were determined by the stored volume and samples were taken to quantify nutrient losses in water (nitrite, nitrate, phosphate and potassium). The losses of water by runoff were highest for the CTDP; intermediate for the treatments CTCP, CoP and MTCP, and lowest for the CP. Potassium (K) was the nutrient that had the highest concentrations and losses in water: the highest values were found in the CTDP and CTCP tillage systems, whereas the lowest were observed for the CP, CoP, and MTCP treatments. The concentrations and the losses by water erosion of phosphate (PO43-), nitrite (NO2-), and nitrate (NO3-) were low in all of the soil tillage systems compared to the losses of K in this study.