Phosphorus Reductions in Runoff and Soils from Land-Applied Dairy Effluent Using Chemical Amendments: An Observation

Abstract

Field application of dairy effluent at nitrogen (N) agronomic rates generally leads to an over-application of phosphorus (P).  A build up of soil P then occurs that can increase the soluble P in rainfall-runoff.  Increases in runoff soluble P can cause surface water quality problems, because P is generally the limiting nutrient to algal growth in freshwater systems.  Chemical amendments may reduce P solubility from effluent application fields by binding P into less soluble forms.  This demonstration was conducted to display the impacts of two amendments, alum and gypsum, to soils and runoff using simulated rainfall conditions on a field historically used for dairy effluent application.  Large decreases in soluble P in runoff and soil extractable P were seen on the alum-amended plot compared to the control.  On the gypsum-amended plot, changes in soluble P concentrations in runoff were not observed, although small but notable decreases in soil P were indicated.  These results indicate that alum may be a suitable chemical amendment for reducing soluble P from dairy effluent application fields.  Long-term, replicated studies under natural rainfall conditions are needed to evaluate the impact of alum not only on runoff and soil P concentrations but also on forage quality and yield.