SEDIMENTS TRANSPORTED FROM AN HAPLUDOX THROUGH WATER EROSION EVENTS

Quantity and size distribution of sediments transported by runoff are influenced by soil management, cover and crop systems, and by rainfall, among other factors, representing an important aspect in soil conservation planning. The objective of this study was to quantify runoff sediments and relate them with runoff velocity, during soybean growth, in a simulated rainfall experiment initiated in 1998 on a typical Hapludox, under the following soil management systems: conventional tillage with one plowing plus two diskings (CT) and no-tillage on a never tilled soil with burned residues (NT). In these treatments, the rotation crop systems consisted of oat, soybean, vetch, corn, oats, bean, fodder radish, soybean, vetch, corn, and soybean. An additional treatment with bare soil with one plowing plus two diskings (BS) was also studied. Five simulated rainfall tests were applied to the treatments in the last soybean crop cycle, with an intensity of 63-67 mm h(-1) for one hour, 24 h after a pre-wetting rainfall, with an intensity of 65 mm h(-1) and long enough to initiate runoff. The sediments were quantified in runoff samples collected 10 minutes before the end of each simulated rainfall test, and were related with the runoff velocity. The sediment size in the runoff was influenced by soil management systems and the rainfall quantity. In the treatment without soil cover (BS), the quantity of coarse sediments was higher than in the treatments with cultivated soil, whereas in CT and NT treatments the quantity of fine-sized sediments was higher than in the BS treatment. More sediments tended to be transported in the runoff with the application of more rainfall events. The sediment quantity transported by runoff was related with the sediment size, fitting to a positive exponential model, while runoff velocity decreased exponentially with increased soil cover. The D(50) index was related with other variables, fitting to the potential model and increasing with runoff velocity.