Nitrogen Surface Runoff from Poultry Manure with Simulated Rainfall.

Runoff N lost during a rainfall event can be important. Once in surface water, reduced N forms such as NH₄–N and organic N can be oxidized resulting in oxygen depletion. This study was conducted to estimate N loss via surface runoff after recent amendment with poultry manure and to assess the effect of manure application rate and incorporation on potential losses. The study was conducted on nine production fields across Iowa during three years on soybean [Glycine max (L.) Merr.] residue and using dry poultry manure. Two poultry manure rates were applied in field–length strips based on total–N, in addition to a control with no manure. Manure incorporation effect on runoff of N was also evaluated. A portable rainfall simulator was used to provide a single rainfall event on small plots within the manure strips. Runoff concentration and load of total Kjeldahl N (TKN) and NH₄–N was significantly decreased by incorporation, approximately 50% for TKN and 90% for NH₄–N. Total Kjeldahl N and NH₄–N concentration and load in runoff increased proportionally to manure rate. The average NO₃–N concentration was below 2.5 mg L^–1 for all treatments and there was no significant effect from manure application. The results of this study show that in a single runoff event shortly after poultry manure application the TKN and NH₄–N losses increase with manure rate, but can be decreased significantly with tillage.