Mixing Alum and Gypsum with Egg Layers Manure to Reduce Phosphorus Loss with Surface Runoff.

This study investigated the impact of mixing egg layer manure with alum or gypsum on P loss with surface runoff as affected by the time between manure application and a runoff event. Field rainfall simulation and snowmelt collection techniques were used after applying P to soybean residue at three sites (one trial per year). Diammonium phosphate fertilizer (DAP), egg layer manure untreated and treated with alum or gypsum were applied at 50 kg P ha^-1. Alum or gypsum were mixed with manure at 32% and 26% of as-is manure, respectively, one week before application in the fall with or without incorporation into the soil or in January to snow-covered ground. Simulated rainfall was applied 1 or 10 days after P application. Devices were installed to collect total natural snowmelt runoff in plots where no rainfall was applied, and simulated rainfall was applied to all plots in early spring. Soil samples were taken before applying P and from selected plots in spring after. Runoff total P (TP), bioavailable P (BIOP), and dissolved reactive P (DRP) were much less for manure than for DAP. Incorporation of P significantly reduced P loss only DAP and only for the runoff event immediately after application. Snowmelt P loss for the winter fertilizer application was two to three times higher than for the fall application, but there was little difference for manure. Manure treated with alum consistently reduced P loss more than gypsum, and the reduction was more pronounced for DRP without manure incorporation. Across all runoff events, alum and gypsum decreased DRP by 39 to 88% and 17 to 58%, respectively. All manure treatments, including manure treated with alum, increased soil pH, so potential soil acidification by alum would not be a problem for treated egg layer manure.