Diffuse Losses of Phosphorus From Agricultural Soils - Status and Preventive Measures in a Nordic Perspective.

Diffuse losses of phosphorus from agricultural soils – status and preventive measures in a Nordic perspective

Lars Bergström^a, Helena Andersson^a, Helena Aronsson^a, Faruk Djodjic^b, Holger Kirchmann^a, Pia Kynkäänniemi^a, Jian Liu^a, Annika Svanbäck^a, Barbro Ulén^a, Ana Villa^b

^aDep. of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, 75007 Uppsala, Sweden

^bDep. of Water and Environment, Swedish University of Agricultural Sciences, P.O. Box 7050, 75007 Uppsala, Sweden

Transport of phosphorus (P) from agricultural fields to rivers, lakes and marine environments causes deteriorating water quality and eutrophication, often leading to severe algal blooms. Much attention during recent years in Sweden has been focused on eutrophication of the Baltic Sea for which the gross P load from agriculture is estimated to contribute about 45% of the total anthropogenic P load. Therefore, one of the most important actions for reducing P loadings to the Baltic Sea is to minimize non-point source emissions of P from agricultural land. Accordingly, several research projects have been started during the past five years, with the aim of testing best management practices (BMPs) to reduce P leaching losses via tile-drains which can constitute up to 60% of the total agricultural P losses or even more. Mitigation practices that have been tested include catch crops, constructed wetlands, liming of subsoil and various manure application strategies. Results from these studies showed that of the 8 catch crops tested, none was able to significantly reduce P leaching before they were exposed to freezing/thawing, whereas constructed wetlands reduced total-P loads by 36% and incorporation of pig slurry in a clay soil by 50% as compared with surface application. However, the losses were overall rather small. The average diffuse P leaching load in Sweden is only 0.4 kg P ha^-1 yr^-1 and detection of small changes in P-loadings over time due to implementation of BMP practices requires long monitoring periods. It is also important to keep in mind that other factors such as weather conditions, soil type etc. also have a profound effect on P losses, which can mask the effects of BMPs. We still believe that even small losses can be reduced substantially through development and implementation of proper BMPs.