Nutrient transfer by runoff under no tillage in a soil treated with successive applications of pig slurry

High rates and successive applications of pig slurry can cause nutrient transfer by surface runoff. The aim of this study was to evaluate the importance of surface runoff in transferring nitrogen (N), phosphorus (P) and potassium (K) under a no tillage system and for successive applications of pig slurry. The research was carried out in the Agricultural Engineering Department of the Federal University of Santa Maria, Brazil, from 2002 to 2007 in a Typic Hapludalf soil. Pig slurry rates of 0, 20, 40 and 80 m3 ha−1 were applied, scattered on the surface, before the sowing of each species in a cultivation sequence. On average 119, 238 and 475 kg ha−1 yr−1 of N; 102, 203 and 406 kg ha−1 yr−1 of P and 43, 87 and 173 kg ha−1 yr−1 of K were added, for rates of 20, 40 and 80 m3 ha−1 of pig slurry, respectively. Samples of water runoff from the soil surface were collected during the entire period and the minerals, N, P and K were determined. Successive applications of pig slurry decreased surface runoff. In relative terms, the K losses were higher than N and P. As regards total nutrients applied through pig slurry, losses through surface runoff were of 2.74, 1.61 and 1.37% of mineral N; 6.29, 5.01 and 3.51% of available P and 17.16, 9.01 and 11.14% of available K, for the three rates of applied pig slurry, respectively. Repeated applications of pig slurry on a no tillage managed soil caused losses of N, P and K from the soil through surface runoff, in the sequence: K > P > N. The losses of N and K are positively related to the volume of surface runoff, whereas the losses of P are positively related to the quantities of P added through pig slurry. Applications of pig slurry along the years decrease the surface runoff.