Title: Acidification delays the microbial mineralization of organic N forms in poultry litter Authors
Submitted to: CSA News
Publication Type: Popular Publication
Publication Acceptance Date: August 27, 2010
Publication Date: October 1, 2010
Citation: Rothrock Jr, M.J., Cook, K.L., Warren, J.G., Eiteman, M.A., Sistani, K.R. 2010. Acidification delays the microbial mineralization of organic N forms in poultry litter. CSA News. 55(10):11-13. Technical Abstract: Poultry litter is a valuable nutrient source for plants which contains high levels of protein, nitrogen and other minerals. While many agronomic benefits of poultry litter exist, one of the largest environmental concerns associated with confined poultry production is the creation and volatilization of ammonia gas from organic N (mainly uric acid and urea) in the litter. Acidification of the litter through the use of dry acids has been shown to both reduce ammonia emissions and increase nitrogen content in the litter. Despite the fact that ammonia production in litter occurs as a result of microbial activity, little is known about the microbiology of the process. Scientists at the USDA-Agricultural Research Service (ARS) in Bowling Green, KY and the University of Georgia, Athens are investigating the microbiology of ammonia production in poultry litter; with specific interest in the role acidification plays in controlling the microbial mineralization of organic N forms in the litter. The goal of this collaborative four month laboratory study was to compare the microbiological and physiochemical effects of the three most commonly used dry acid amendments (Al+Clear®, Poultry Litter Treatment®, Poultry Guard®) and to specifically correlate uric acid and urea contents of these litters to the microbes responsible for their mineralization. Results from the study were published in the September-October 2010 issue of the Journal of Environmental Quality. The research was also presented in Pittsburgh, PA at the 2009 Joint Annual Meeting of the ASA-CSSA-SSSA in November 2009. Acidification of the litter significantly affected both the organic N dynamics and the microbial groups responsible for the mineralization of uric acid and urea. Within 2 – 4 weeks after acidification, both uric acid- mineralizing and urea-mineralizing fungi increased by more than two orders of magnitude, whereas the bacterial groups responsible for these mineralization reactions were reduced by 70% to 90%. While uric acid and urea mineralization occurred within the first 2 weeks in the untreated control litter, acidification resulted in delayed mineralization of both uric acid and urea (2 and 4 week delay, respectively). The mineralization of both organic N forms were significantly correlated to these shifts in uric acid- and urea-mineralizing microbial communities from bacteria to fungi. In fact, organic N mineralization did not occur in the acidified litter until fungal cell concentrations exceeded a threshold level. All three dry acid amendments tested eventually produced similar results, but litter treated with Poultry Litter Treatment displayed a 2 week delay in microbial responses to acidification. Michael J. Rothrock, Jr., who conducted the study, stated “This study represents the first report of uric acid and urea data from dry acid treated litters, with their direct correlation to the microbial populations responsible for their mineralization. These results demonstrate the importance of fungi in the mineralization of organic N in low-pH, high-N environments, and the activity of uric acid- and urea-mineralizing fungi should be considered in best management practices to reduce ammonia volatilization from acidified poultry litter.” The results of this study can be used by both scientists and producers to develop more effective litter amendment strategies by directly targeting the microbial ammonia producers. For example, current research at the USDA-ARS in Bowling Green, KY is focusing on controlling both the bacterial (using dry acid amendments) and fungal (using fungicides) ammonia producers in poultry litter. The ultimate goal is to find ways to inhibit both bacterial and fungal ammonia producers so that farmers are able to retain the nitrogen value of the litter and reduce the negative effect of ammonia production on the birds and the environment.