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 NH 3 volatilization. We conducted 11 field studies to determine overall NH 3 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 H 2 O g soil −1 ) decreased overall NH 3 losses, potentially due to N movement into the soil. In the remaining nine studies, average vapor pressure (VP) and initial NH 4 –N plus uric acid‐N (ANUA) explained 79% of the variability in cumulative NH 3 loss over 28 d. Our data suggest that elevated concentrations of initial uric acid‐N and NH 4 –N, as well as, elevated VP increase NH 3 losses. The effect of elevated VP on NH 3 losses was attributed to the rewetting of the litter, which likely leads to increased N mineralization and NH 4 –N in solution. The statistical model developed may help estimate NH 3 losses from surface‐applied litter and increase the accuracy of estimating available N under field conditions.