Evaluation of chemical amendments to control phosphorus losses from dairy slurry.

Abstract

The aim of this paper is to identify chemicals with the potential to reduce P losses from agricultural grassland arising from the land application of dairy cattle slurry. It also aims to identify optimal application rates and to estimate associated costs. The cost of chemical amendments was estimated based on cost of chemical, chemical delivery, addition of chemical to slurry, volume increases during slurry agitation, and slurry spreading costs. First, batch tests were carried out to identify appropriate chemical and phosphorus sorbing materials (PSMs) to be considered as potential amendments to control P in runoff from dairy cattle slurry. Then, the best seven treatments were examined in a novel agitator test. Optimum application rates were selected based on percentage removal of dissolved reactive phosphorus (DRP) in overlying water and the estimated cost of amendment. At optimum application rates, alum reduced the DRP in overlying water by 94%, aluminium chloride (AlCl2) by 92%, ferric chloride (FeCl2) by 88%, lime by 81%, aluminium water treatment residuals (Al-WTR; sieved to <2mm) by 77%, Al-WTR sludge by 71%, flyash by 72%, and flue gas desulphurisation by-product by 72%. Alum was the most cost-effective chemical amendment, and was capable of greater than 90% reduction in soluble P in overlying water. The optimum FeCl2 amendment was less expensive, but not quiet as effective. AlCl2 and lime are expensive, and despite the attractiveness of using PSM, those examined were not cost effective at P reductions of greater than 85%.