Factors Affecting Ammonia Loss from Pastures Fertilized with Broiler Litter

Broiler litter is commonly surface-applied to pasture in the southeastern United States as a method of waste management and to provide an inexpensive source of plant nutrients, such as N. However, predicting plant available N derived from litter can be difficult due to losses through NH3 volatilization. We conducted 11 field studies to determine overall NH3 loss as affected by environmental variables and litter characteristics. Ammonia loss as a percentage of the applied total N (TN) ranged from 0.9 to 10.5% in eleven 28-d studies conducted from April to November in 2011 and 2012. In two studies, a series of small rain events (2-5 mm) combined with elevated soil water content (WC) (>0.2 g H2O g soil(-1)) decreased overall NH3 losses, potentially due to N movement into the soil. In the remaining nine studies, average vapor pressure (VP) and initial NH4-N plus uric acid-N (ANUA) explained 79% of the variability in cumulative NH3 loss over 28 d. Our data suggest that elevated concentrations of initial uric acid-N and NH4-N, as well as, elevated VP increase NH3 losses. The effect of elevated VP on NH3 losses was attributed to the rewetting of the litter, which likely leads to increased N mineralization and NH4-N in solution. The statistical model developed may help estimate NH3 losses from surface-applied litter and increase the accuracy of estimating available N under field conditions.