The transport of pollutants via runoff in agricultural areas, mainly in soluble forms, is an environmental problem, even in conservation tillage systems. The objective of this study was to evaluate losses of nitrogen and organic carbon in runoff, after applications of 0, 60, 120, and 180 m³ ha-1 yr-1 of cattle slurry to a clayey Oxisol, with 10 % slope under no-tillage and natural rainfall, in the region of Castro - PR. The application of cattle slurry did not affect total organic carbon in runoff but ammonium and nitrate losses were reduced by the fertilization with 120 m³ ha-1 yr-1 of slurry, indicating this as the maximum dose recommended for soils with a high clay content, moderate slope and low rainfall, with at least one week interval between manure application and rainfall. The weighted average concentrations of ammonium and nitrate increased with manure application. The ammonium concentrations exceeded the threshold established by the Brazilian law by far, even in the treatment without slurry application, indicating the need for practices that prevent runoff from entering watercourses, even in conservation tillage systems.
runoff; water quality; nutrient; nitrate; ammonium; organic fertilizer
