Sam Marshall, Wes Wood, and Elizabeth Guertal

Nitrogen (N) applied in the form of broiler litter can both benefit crop production and adversely affect the environment. One area of environmental concern is the tendency for ammonia (NH₃) in the litter to volatilize, or turn into a gaseous form, and escape into the atmosphere. An AAES study examined the rate of volatilization of ammonia from field-applied broiler litter, and results suggest that NH₃ volatilization is not a major pathway for N loss from broiler litter applied to tall fescue in spring in Alabama.

Broiler litter, a mixture of manure and locally available bedding material (wood shavings, peanut hulls, rice hulls, etc.), is a byproduct of the Southeast's thriving broiler chicken industry. In an effort to solve waste disposal problems while providing farmers a low-cost, effective N source, broiler litter has been applied to both crop and forage systems. However, many uncertainties exist as to the efficiency of poultry litter as a N source as well as to several possible environmental hazards of using broiler litter as a fertilizer. Several of these uncertainties and hazards stem from the potential for NH₃ volatilization following land application. Ammonia lost to the atmosphere cannot benefit crops and also can cause environmental problems such as acid rain.

If NH₃ is not bonded to another particle, such as in decomposing manures or in a patch of dissolving urea fertilizer, then it will be volatilized. NH₃ typically volatilizes rapidly following application of animal manures and a significant portion of the applied N can be lost. Previous studies have shown that NH₃ losses from poultry litter may range from 3.6 to 60% of total N applied. AAES researchers conducted a study to determine the rate and amount of N loss through NH₃ volatilization from broiler litter applied to tall fescue pastures in Central Alabama.

Plots were established at the E.V. Smith Research Center in Shorter within established fescue pastures. In the spring of 1995 and 1996, broiler litter was applied to each plot at a rate to supply 62.5 pounds available nitrogen per acre. Ammonia volatilization was measured using a field scale technique each 24-hour period for 14 days following litter application.

Rate of NH3 volatilization

A sharp increase in NH3 volatilization in response to broiler litter application, especially in the first four days after application, was observed during both years (see figure). Peak volatilization rate was 0.8 pounds NH3-N per acre per day in 1995 and 1.9 pounds NH3-N per acre per day in 1996. However, NH3 volatilization rates decreased rapidly to normal levels within 10 days after application.

Total N lost due to NH₃ volatilization during 14 days after litter application ranged from 3.4 pounds NH₃-N per acre in 1995 and 3.9 pounds NH₃-N per acre in 1996. Expressed as a percentage of total N applied, the impact of NH₃ volatilization becomes more clear, with losses ranging from 2.7% in 1995 to 3.8% in 1996.

These losses are lower than those reported in other studies involving poultry litter. However, the majority of NH₃ volatilization studies with poultry litter have been laboratory incubations of litter/soil mixtures or litter only. An earlier field study of NH₃ volatilization from surface-applied turkey manure reported total losses of N of only 7% of total N applied, which is comparable to losses observed in the AAES study.

The relatively small losses of N due to NH₃ volatilization observed in this study may be explained by several factors. One possible explanation may be the dense and actively growing plant cover on these pastures at the time of litter application and during the sampling period. This could have caused a more rapid plant uptake of NH₃ and also absorption of volatilized NH₃ by plant leaves. A second possible explanation for the low NH₃ volatilization losses observed in this study centers around moisture. In general, dry soil conditions and low relative humidity enhance NH₃ volatilization. The sampling periods for this study were characterized by high humidity, heavy dews, and high soil moisture, all of which could have contributed to the relatively low amounts of N lost via NH₃ volatilization.

Temperature is another factor that may help explain why the rates of NH₃ volatilization in this study were less than that of previous studies. Ammonia volatilization generally increases with increasing temperature. The majority of previous studies involving poultry litter have been lab incubations at approximately 77^oF, while the AAES measurements were at field conditions that averaged 65^oF. This may have been a large enough difference to produce this study's lower NH₃ volatilization rates and reduced N losses compared to previous studies. Relatively low amounts of N lost via NH₃ volatilization in this study compared to other studies is likely a combination of these factors, and possibly others.

The data from this study indicate that NH₃ volatilization was not a major pathway for N loss from broiler litter applied to tall fescue in the spring at this site in Alabama. Amounts of N volatilized in this study would not significantly decrease yield of most forage crops. The increase in NH₃ volatilization due to broiler litter was essentially concluded six to 10 days after application. This time frame could be important in timing of future attempts to control NH₃ volatilization.

This study indicated that land application of broiler litter did not increase NH₃ volatilization to the point of significant contribution to environmental degradation based on established critical loads for total N deposition. In forage systems of the Southeast, other pathways (denitrification, leaching, soil accumulation, etc.) are more likely to contribute to environmental degradation and/or economic loss. Future studies should focus on these pathways.