Phosphorus losses in the drainage water of wet soils used as grassland

Nutrient losses from agricultural systems should be avoided for ecological and economical reasons. The leaching of phosphorus into the drainage water was investigated in a catchment area of about 10 ha used as grassland in the village of Reichenburg (SZ, Linthebene). The main factors that affect phosphorus leaching into the drainage water are precipitation, soil type, land use, fertilization and groundwater level. These investigations have shown that phosphorus leaching in the studied catchment area depended mainly on the extent and time of precipitation events (annual precipitations of 1550 mm to 2050 mm). The application of liquid manure immediately before rainfall had also an impact on phosphorus leaching. The total annual phosphorus losses trough drainage, which were based on periodically measured values, were 1.4 kg to 8.1 kg P/ha between 1998 and 2001 in this catchment area. The proportion of the dissolved phosphorus, mostly responsible for the eutrophication of surface water, was about 10 to 55 % of the total phosphorus. Adapted land use and optimal fertilization in agricultural systems may contribute to a reduction of phosphorus losses in a catchment area with a high risk of nutrient losses.