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A major concern of the broiler industry is the volatilization of ammonia (NH3) from the mixture of bedding material and broiler excretion that covers the floor of broiler houses. Gypsum has been proposed as a litter amendment to reduce NH3 volatilization, but reports of NH3 abatement vary among studies and the mechanism responsible for decreasing NH3 volatilization is not well understood. The goal of this study was to evaluate the effect of adding 20 or 40% flue-gas desulfurization gypsum (FGDG) to broiler litter on pH, electrical conductivity (EC), water potential, urea-degrading bacteria abundance, NH3 and carbon dioxide (CO2) evolution, and nitrogen (N) mineralization in several 21-d experiments. The addition of FGDG to broiler litter increased EC by 24 to 33% (P < 0.0001), decreased urea-degrading bacteria by 48 to 57% (P = 0.0001) and increased N mineralization by 10 to 11% (P = 0.0001) as compared to litters not amended with FGDG. Furthermore, the addition of FGDG to broiler litter decreased NH3 volatilization by 18 to 28% (P < 0.0001), potentially resulting from the significantly lower litter pH values compared to un-amended litter (P < 0.0001). Findings of this study indicate that amending broiler litter with 20% FGDG can decrease NH3 volatilization and increase the fertlizer value of broiler litter. [ABSTRACT FROM AUTHOR]

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 con- tent (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 estimat- ing available N under field conditions. [ABSTRACT FROM AUTHOR]

Previous work showed that simulated rainfall applied immediately after urea application to a pine forest floor decreased NH3 losses to negligible levels. The same work also showed that unless rain occurs before urea is dissolved, it might not be effective at leaching urea into the forest floor and decreasing NH3 losses. This study evaluated the effects of diurnal humidity cycles and rainfall amounts on the proportion of urea leached from loblolly pine (Pinus taeds L.) forest floor fractions, and on subsequent ammonia volatilization. New and old pine needles, as well as the partially decomposed (Oe) horizon, were collected from a loblolly pine forest floor in Georgia, USA. Control samples and samples treated with urea at 200 kg N ha-1 were exposed to zero, two, four, or eight simulated humidity cycles, after which they were leached with nine 20-mm increments of simulated rain. Rainfall (180 mm) applied immediately after urea application (0 humidity cycles) leached >98% of the urea from the three forest fractions. Increasing the number of simulated humidity cycles from zero to eight decreased the percentage of urea leached from new pine needles from 98 to 49%, but did not have a major effect on the amount of urea leached from old needles or partially decomposed fraction. All of the urea not leached from new pine needles by 180 mm of simulated rainfall was extractable by water when the new needles were ground. When new needles treated with urea were leached with 180 mm of simulated rainfall and then incubated at 25°C and 95% relative humidity (RH) for 15 d, NH3 losses amounted to 8% of the urea applied. These results suggest that urea retained by recently dropped pine needles is found inside the needles, where it can be hydrolyzed and subsequently lost as NH3. [ABSTRACT FROM AUTHOR]