WATER, SOIL AND PHOSPHORUS LOSS AFTER CATTLE SLURRY APPLICATION TO OXISOL UNDER NO-TILLAGE AND SIMULATED RAINFALL

Campos Gerais in the State of Parana (Brazil) is an important region of milk production and consequently of cattle slurry. The purposes of this study were: (a) to evaluate losses of water, soil, total P, soluble P and particulate P under simulated rainfall performed immediately after the application of 0, 30, 60 and 90 m(3) ha(-1) cattle slurry on a Red-Yellow Latossol (Ferralsol) under no-tillage system, and (b) to discuss the possible impacts on water quality. Slurry application increased the surface runoff rate by more than 10 times in all 15 min intervals of the 2 h rainfall. The increase of total runoff was highest between 0 and 30 m(3) ha(-1), and tended to stabilize at over 60 m(3) ha(-1). The soil loss rate in the first 15 min of rainfall also increased with slurry application, and this tendency continued until the end of the 2 h rainfall, although not significantly. The highest increase of total soil loss was also observed between 0 and 30 m(3) ha(-1), tending to stabilization at the highest slurry dose. Part of the solid runoff was derived from the applied slurry. The application, even at only 30 m(3) ha(-1) slurry, increased the total, soluble and particulate P concentration in the runoff to over the limit values regarding eutrophication, especially in the first 15 min of rainfall. Besides the increased runoff rate and P concentration, the slurry application also caused higher absolute losses of the three P forms, which tended to stabilize from 60 m(3) ha(-1) onwards. The increase in runoff and soil and P loss rates were possibly due to soil surface sealing caused by slurry particles and is possibly related to the fact that rainfall was simulated immediately after slurry application.