CORRELATIONS BETWEEN CONCENTRATIONS OF PLANT NUTRIENTS IN RUNOFF FROMSMALL CATCHMENTS IN NORWAY

Factor analysis investigated the relationship between different compou nds of nitrogen, phosphorus, potassium and suspended dry matter in run off from catchments in agricultural areas in southern and central Norw ay. The plant nutrients were grouped in three factors: phosphorus fact or, nitrogen factor and erosion factor. In south-eastern Norway there was a significant correlation between runoff and concentration levels of phosphorus and suspended dry matter in winter and spring erosion pe riods. Climate, agricultural practices and soil conditions caused seas onal variation of the different factors. In the catchments in southwes tern Norway there was a decreasing trend in concentration level of nit rogen due to changed practice for slurry application. In the catchment s in eastern and central Norway there was a decreasing concentration l evel of phosphorus. The reduction in applied phosphorus was 15-50% but the decrease in concentration level of phosphorus in runoff accounted for 5 to 15% of the variation.