Evaluation of Amendments to Control Phosphorus Losses in Runoff from Dairy-Soiled Water

Amendments with the potential to reduce phosphorus (P) losses from agricultural grassland arising from the land application of dairy-soiled water (DSW) were investigated. Optimal application rates were studied, and associated costs and feasibility were estimated. First, batch tests were carried out to identify appropriate chemicals or phosphorus sorbing materials to control P in runoff from DSW. Then, the best four treatments were examined in an agitator test. In this test, soil??placed in a beaker??was loaded with DSW or amended DSW at a rate equivalent to 5 mm ha^?1 (the maximum permissible application rate of DSW allowable in a 42-day period in Ireland). The soil was overlain with continuously stirred water to simulate runoff on land-applied DSW. Optimum application rates were selected based on percentage removal of dissolved reactive phosphorus in overlying water and the estimated cost of amendment. The costs of the amendments, per cubic metre of DSW, increased in the order: bottom ash (1.55 ?), alum (1.67 to 1.92 ?), FeCl₂·4H₂O (3.55 to 8.15 ?), and lime (20.31 to 88.65 ?). The feasibility of the amendments, taking into account their cost, potential adverse effects, public perception, and their performance, decreased in the order: alum?>?FeCl₂·4H₂O?>?bottom ash?>?lime. Amendments to DSW could be introduced in critical source areas??areas where high soil test P and direct migration pathways to a receptor overlap.