Magasin för lagring av vatten och växtnäring

Abstract: Structural rationalizations and regionalization of the agricultural sector in Sweden has lead to unevenness in thedistribution of plant nutrients. Nutrients are lost from crop producing farms as harvest products are sold, whilefarms with animal production often have manure in excess of their needs. In addition to this the retention ofwater and nutrients in naturally occurring wetlands has decreased due to a reduction of wetlands in number andsize in the agricultural landscape. This increases nutrient levels in agricultural run-off and causes eutrophicationas well as nutrient losses from arable soils. One potential solution to both problems would be to store nutrientrichsurface water from agricultural areas and use it for irrigation of agricultural crops. This thesis is a study onthe water and nutrient flows between four irrigation ponds, the irrigated fields and the streams from which wateris pumped into storage. It was found that the amount of nitrogen (N) and phosphorus (P) that had been gatheredin the different ponds varied a lot between ponds, due to differences in nutrient levels in the streams and todifferences in when ponds were filled. A maximum of 98 kg of N and 0.4 kg of P were collected in one of theponds. Only small amounts of nutrients were brought back to the fields with irrigation, at the most 5 kg of N and0.07 kg of P. It was concluded that the practice of irrigating agricultural crops with nutrient-rich surface waterdid not contribute much to nutrient demand, but it decreased nutrient transport further downstream as effectivelyas an average wetland.