FORURENS: Critical level of P in soil and sediments related to risk of eutrophication, and optimising supply and utilization of P in agricul

Water quality in lakes, streams and rivers in districts with considerable agricultural activity, is largely classified as poor to very poor, due to large inputs of nutrients, in particular phosphorus. The negative development in water quality in spite of considerable abatement erosion strategies to reduce P runoff show that it is necessary also to reduce the P sources, i.e. the level of plant available P in the soil. High PAL level may also influence the lake sediment properties to adsorb and release P an d may therefore both directly and indirectly influence on the water eutrophication processes. P is a limited resource world wide. A better utilization of P in the soil and an optimisation of applied P in agriculture are needed both with regard to agricult ure and the environment. The focus in the project is: · To study the effect of high PAL levels in soil on water soluble P and on the equilibrium P concentration in particle effected water, and how it effects lake sediment sorption chemistry and the poten tial for biological growth in water. In that respect information on plant available P in soil is used to evaluate both risk of eutrophication and the need for fertilization. · To calibrate the Norwegian P Index for implementation into the environmental a nd fertilization plans on farm field level as a new strategy to reduce the agricultural P load to water. · Evaluation of the fertilization norms and improving the calculation for P in the fertilization programs by use of field experiment results to obtai n a more balanced use of fertilizers to minimize the risk of eutrophication.