Runoff Nitrogen Loss with Simulated Rainfall Immediately Following Poultry Manure Application for Corn Production

Abstract

Nitrogen loss from a soybean [Glycine max (L.) Merr.]–corn (Zea mays L.) rotation by runoff to surface water can be significant. This study was conducted to determine short‐term N loss in runoff immediately after poultry manure application and assess the effects of manure rate and incorporation on losses. The study was conducted for 3 yr at nine Iowa fields previously cropped to soybean. Poultry manure sources were applied in the fall or spring to untilled soybean stubble at intended rates of 0, 84, and 168 kg total N ha−1with three replications. Within 2 d of application, simulated rainfall was applied to 3‐m2 areas to provide a single 30‐min runoff event. The total Kjeldahl N (TKN) and NH4+–N concentration and load in runoff increased with higher manure rates, with the associated manure TKN and NH4+–N correlated with runoff losses. With the high manure rate, runoff TKN and NH4+–N concentration averaged 33 and 15 mg L−1 and the TKN and NH4+–N load 2.6 and 1.1 kg ha−1, respectively. Runoff concentration and load of TKN and NH4+–N was significantly decreased with incorporation, approximately 50% and 90%, respectively. Tillage increased TKN in runoff when no manure was applied, but loses were lower than the treatment with manure and incorporation. The NO3−–N load in runoff was low and not affected by manure application. The results show that rainfall shortly after surface application of poultry manure can result in increased runoff TKN and NH4+–N, with loss related to manure rate, specific N fraction, and incorporation, which significantly reduced manure N in surface runoff.