Phosphorus Runoff Losses from Surface Applied Fertilizer and Different Types of Poultry Manure.

A field rainfall simulation study was conducted to assess runoff P loss shortly after applying P fertilizer and different types of poultry manure (from egg layers, broilers, and turkeys) without incorporation into the soil. The manures and diammonium-phosphate fertilizer were applied at 50 kg P ha^-1 with three replications at 16 fields after soybean harvest. Total P concentration in layer, broiler and turkey manures were 7-63, 9-40, 15-51 g P kg^-1 on a wet basis, respectively and water-soluble P was 1-5, 1-6 and 2-7 g P kg^-1 respectively. Simulated-rainfall (71 mm hr^-1) was applied to field plots until 30 minutes of runoff was collected. Runoff P concentrations were significantly larger for fertilizer, and on average they were 15, 16, and 21 mg L^-1 dissolved reactive P (DRP), bioavailable P (BAP), and total P (TP), respectively. Runoff P concentrations for poultry manure were much less, and differences among the three manure types were inconsistent across sites. On average across manure types runoff P concentrations were 1.9-2.9, 2.3-3.3, and 3.7-4.5 mg L^-1 DRP, BAP, and TP, respectively. There was large variation across sources within each manure type that was explained mainly by the physical characteristics of the manure. The ranking for runoff P loads was similar to concentrations. Water-extractable P in the manure was poorly correlated with runoff P loss across manure types and sites. Results indicate that risk assessment indices of short-term P loss should account for the P source but the water solubility of manure P is an unreliable estimator of risk of P loss across poultry manure types and fields.