Modeling Ammonia Volatilization From Surface-Applied Broiler Litter.

Broiler litter is a valuable source of plant available nitrogen for pastures and crops. However, large losses of N (nitrogen) to the atmosphere through ammonia volatilization can lead to low crop yields and environmental contamination. Ammonia volatilization is dependent on many factors: manure management, soil characteristics, and environmental conditions. Environmental conditions may be most influential for surface application of broiler litter to pastures.  The objective of this study was to model ammonia volatilization from surface applied litter dependent on environmental variables.  Ammonia loss was measured with an integrated horizontal flux method during 11 28-day studies between the months of April and November in 2011 and 2012.  Litter was applied at a rate of 120 kg total N ha^-1 for each study (four replications per study).  Ammonia was trapped and measured biweekly. Relative humidity, temperature, rainfall, vapor pressure, dew point, leaf wetness, air temperature and soil water content were measured onsite at 5 minute intervals.  Ammonia loss ranged from 1.1 to 9.9% of the N applied.  Cumulative ammonia loss was related to both average vapor pressure and the initial ammonium concentrations of the litter applied.  Increased vapor pressure may lead to increased litter water content and increased mineralization on the pasture surface, subsequently, increasing ammonia loss.