Eutrophication from Agricultural Sources - Phosphorus and Nitrogen

Eutrophication from Agricultural Sources - Phosphorus and Nitrogen

This document is a summary of the conclusions and recommendations that have been compiled from those listed in final reports submitted under LS-2.1 and LS-2.2 to date. Scientific conclusions have been compiled and integrated into recommendations that have implications for agriculture and water quality managers are based on scientific findings from the above research projects. Conclusions: The conclusions (to date) from the research conducted in LS2.1 and LS2.2 fell broadly into the following categories; i) land use ii) soil type iii) management iv) climate v) catchment size and vi) modeling tools. Land Use: The general conclusion from the catchment studies confirmed that managed grasslands are a significant source of nutrient loss to water (1.6-2.8 kgP/ha/yr). Other land use categories such as tillage and forestry were identified from a literature review. Soil Type :Soil type was shown to affect the drainage patterns and P chemistry of grassland soils and drainage class and chemical parameters such as %OM and pH influenced the quantity and quality of P exported in catchments. Saturation excess overland flow was identified as the dominant form of overland flow and the expanding variable source area (VSA) hydrology with freely desorbable P was responsible for the increase in P concentration with flow in overland flow.Management: Management factors affecting P loss to water identified in the research included the presence of grazing animals, timing of slurry spreading, fertilizer use and soil P levels. Grazing affected the quantity and quality of overland flow due to compaction and the presence of the grazing animal. Grazing animals and dung deposition affected cycling in grazed pastures and dung pats significantly increased soil test P levels and total inorganic P in soil. Fertiliser inputs and soil P levels in grazed pastures affected herbage P which in turn affected total P in dung and the distribution of soil P fractions such as water soluble P total inorganic and organic P. Fertiliser use on grassland farms matched advice given with fertilizer use on tillage systems greater than that advised. In general the higher the fertilizer P application rate the higher the potential for P loss to water. Fertiliser applications affected the complex interactions of soil nutrient that lead to a release of nutrients in overland flow.

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Environmental Protection Agency 2000-LS-2-M2
Owen Carton

Keywords: Eutropication; Agriculture; Phosphorus; Nitrogen

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