Phosphorus and potassium losses by water erosion in an inceptisol under natural rainfall

Inadequate soil management systems can lead to water erosion, nutrient losses and superficial water pollution, accelerating environmental degradation. The P and K losses caused by water erosion were evaluated from November 1999 to October 2001 in an Inceptisol with 0.102 m m(-1) slope, in Lages, Santa Catarina State, Brazil, under natural rainfall conditions. The evaluated soil management systems were: no-tillage for six years (NT6), no-tillage for nine years (NT9), chiseling plus one disking for nine years (C + D-9), and plowing plus disking twice for nine years (P + D-9). All of these treatments were carried out in duplicate. One experimental plot was cultivated with bean, vetch, corn, and oat in rotation, and the other with soybean, wheat, soybean, and wheat in succession. An additional treatment consisted of bare soil (control), which was periodically tilled with plowing plus disking twice for nine years (BS9). The P and K contents were determined in runoff water and sediments. Both P and K concentrations were higher in runoff water and sediments under the conservation soil tillage than under conventional soil tillage. Total K losses were higher in the runoff water than in the sediment, except in the BS9 treatment. Regarding P losses, they were higher in water than sediment only in the NT6 and NT9 tillage. In the runoff water, the total P losses were higher in NT6 and NT9 tillage, while the K losses varied with conservational tillage and conventional tillage, with no clear trend. Potassium losses in the runoff sediment were smaller in conservational tillage, but those of P were only smaller in NT6 and NT9 treatments.