Nutrient losses over time via surface runoff and subsurface drainage from an agricultural field in northern Sweden.

Nitrogen (N) and phosphorus (P) losses, via both surface runoff and subsurface drainage water, were monitored in an agricultural field in northern Sweden for 32 yr. The objective was to determine losses of N and P in a long-term perspective in relation to meteorological factors and impacts of agricultural land use, with a focus on relative contributions of surface runoff and subsurface drainage water to N and P losses. In order to collect surface runoff water, an embankment was installed on three sides of the field, and the fourth side had an open ditch that drove runoff water to a measuring station. Subsurface water draining from the field was collected in a fishbone-shaped drainage system that terminated at the measuring station. In 50% of years (16/32), mean annual concentration of total N (TN) was significantly higher in subsurface drainage water than in surface runoff water. An opposing trend was seen for total P (TP), with mean annual concentration being significantly higher in surface runoff water than in subsurface drainage water in all but 3 of the 32 yr monitored. Years with a barley crop had higher TN concentration in subsurface drainage water but no difference in surface runoff compared with years with ley. In contrast, years with barley had lower TN concentration in surface runoff than years with ley, with no difference in TP in subsurface drainage water.

Reducing agricultural nutrient surpluses in a large catchment - Links to livestock density.

The separation between crop- and livestock production is an important driver of agricultural nutrient surpluses in many parts of the world. Nutrient surpluses can be symptomatic of poor resource use efficiency and contribute to environmental problems. Thus, it is important not only to identify where surpluses can be reduced, but also the potential policy tools that could facilitate reductions. Here, we explored linkages between livestock production and nutrient flows for the Baltic Sea catchment and discuss management practices and policies that influence the magnitude of nutrient surpluses. We found that the majority of nutrients cycled through the livestock sector and that large nitrogen and phosphorus surpluses often occurred in regions with high livestock density. Imports of mineral fertilizers and feed to the catchment increased overall surpluses, which in turn increased the risk of nutrient losses from agriculture to the aquatic environment. Many things can be done to reduce agricultural nutrient surpluses; an important example is using manure nutrients more efficiently in crop production, thereby reducing the need to import mineral fertilizers. Also, existing soil P reserves could be used to a greater extent, which further emphasizes the need to improve nutrient management practices. The countries around the Baltic Sea used different approaches to manage agricultural nutrient surpluses, and because eight of the coastal countries are members in the European Union (EU), common EU policies play an important role in management. We observed reductions in surpluses between 2000 and 2010 in some countries, which suggested the influence of different approaches to management and policy and that there are opportunities for further improvement. However, the separation between crop and livestock production in agriculture appears to be an underlying cause of nutrient surpluses; thus, further research is needed to understand how policy can address these structural issues and increase sustainability in food production.