Effect of tillage on sediment and phosphorus losses from a field and a catchment in south eastern Norway

Erosion and loss of soil is a large problem for water quality all over the world. Mitigation measures need to target the main sources of erosion at the right scale. For many areas there is still great uncertainty at the catchment level as to what are the main sources of erosion and how they can be managed. The objective of this article was to investigate the effect of tillage on soil losses at the field and catchment scale. Long-term monitoring data (20 years) from a catchment and a nested field site in the south eastern Norway were used. Results from the Vandsemb field showed that soil losses were on average 940 kg ha(-1)yr(-1) for years (n = 5) when the field was autumn ploughed and 174 kg ha(-1)yr(-1) for years (n = 8) when the field was not tilled in autumn. For the total monitoring period, surface soil losses were 330 kg ha(-1)yr(-1), whereas subsurface soil losses were 130 kg ha(-1)yr(-1). Total phosphorus and dissolved reactive phosphorus (DRP) losses in surface runoff were 460 g ha(-1)yr(-1) and 150 g ha(-1)yr(-1), respectively and in sub-surface runoff they were 530 g ha(-1)yr(-1) and 270 g ha(-1)yr(-1), respectively. At the catchment scale, no relationship was found between the soil tillage on agricultural fields and the variation in losses of suspended sediments (SS) at the catchment scale. The average losses at Mordre were for suspended sediments 2140 kg ha(-1)yr(-1), for total phosphorus 2320 g ha(-1)yr(-1), and for DRP 240 g ha(-1)yr(-1). Weather conditions, especially during winter, were important for the temporal variation in losses of SS at both sites. Soil losses from the Mordre catchment were approximately five times higher than from the Vandsemb field. The study findings suggest that changes in soil tillage were not the dominating cause of variations in loss of SS from the catchment, although these changes were important at the field scale.