Critical Source Areas of Nutrient Losses from Agriculture in Norway

Nutrient losses from agriculture have caused impaired water quality for decades in Norway. Therefore, long-term monitoring of soil and nutrient losses has been carried out in agriculturally dominated catchments differing in soils, climate and agricultural production. Total phosphorus (TP) losses varied from 0.4 kg ha(-1) to 9.6 kg ha(-1). A catchment dominated by potato and vegetable production, Vasshaglona, had the highest loss of TP. Runoff in the Vasshaglona catchment was relatively high (1250 mm y(-1)) compared to the other catchments, and partly responsible for the high loss of TP. Further, the concentration of TP in the Vasshaglona stream was higher (490 mu g L-1) compared to the other agricultural streams (60-390 mu g L-1). Long-term history of P application above P uptake was reflected in a high soil P status. The mean P application rate in the Vasshaglona catchment was 52 kg ha(-1) for the monitoring period. The concentration of TP in the stream was closely related to transport of suspended sediments. Open, uncovered soil, plant residues and high nutrient surplus contributed to the high nutrient loss. These results confirm that areas of vegetable/potato production are often hot spots regarding nutrient loss from agriculture. Focus on improved management of soils and nutrient sources (fertiliser and manure) in vegetable and potato production, is a prerequisite for a successful mitigation strategy for reduced nutrient losses from agriculture.