Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 6, 2008
Publication Date: January 1, 2009
Citation: Brooks, J.P., Adeli, A., Read, J.J., McLaughlin, M.R. 2009. Rainfall simulation in greenhouse microcosms to assess bacterial-associated runoff from land-applied poultry litter. Journal of Environmental Quality. 38:218-229. Interpretive Summary: Poultry litter land application is an environmentally-sound method of disposing and utilizing this waste product. The farmer who used poultry litter can find organic forms of N and P which can be readily used by crops. However, some concerns exist, due to the fecal nature of the product. Since poultry litter is a fecal product it can be potentially contaminated with harmful bacteria (disease causing and drug resistant) which can contaminate and pollute crops and surface water. In this study, poultry litter was applied to greenhouse soil trays and rained on using a rain simulator. The rain simulator and greenhouse allow the study of microbial runoff associated with poultry litter land application using controlled conditions. Various bacteria were measured including pathogenic (disease causing) and fecal indicator (used as an alternative to measuring pathogens) bacteria. Following 5 rain events, it was determined that alternative indicators would prove to be more suitable for poultry litter as typical fecal indicators, such as general Escherichia coli (E. coli), and did not perform well. The most suitable bacterial indicators proved to be Clostridium perfringens and enterococci. These two bacterial fecal indicators can be used in determining potential runoff contamination associated with poultry litter. Overall, this study determined that runoff can occur after land application of poultry litter; however no “frank” pathogens (disease causing in both healthy and non-healthy individuals) were detected in applied litter after a hold step of 7 days and hence none were detected in runoff.
Technical Abstract: Land application of poultry litter is an economically and environmentally viable use of this poultry-rearing byproduct. However the recent concern associated with food and surface water contamination with pathogenic and fecal indicator bacteria, nutrients, and colloidal particles has led to increased scrutiny regarding land applied manures and wastes. Runoff following a rain event is one possible source of environmental contamination resulting from manure application. In this study a series of treatments involving a high and low litter rate, a lime-treated litter rate, inorganic fertilizer, and no fertilizer controls were added to bermudagrass troughs and held in a greenhouse to determine the potential for runoff and to select for runoff fecal indicators. A rainfall simulator was used to simulate precipitation events and following each rain event, runoff samples were collected for microbial analyses. Total Heterotrophic Plate Count (HPC) bacteria, total and thermal-tolerant coliforms, enterococci, staphylococci, Clostridium perfringens, Salmonella, and Campylobacter were investigated. In addition, antibiotic resistance was also investigated for staphylococci and enterococci isolates. No Salmonella or Campylobacter were detected in the applied litter following a hold period of 7 days. Over a period of 26 days, 5 rain events were simulated and results indicated that staphylococci, enterococci, and clostridia correlated directly with manure application. Runoff release of staphylococci, enterococci, and C. perfringens were approximately 3 to 6 log10 greater in litter applied versus control plots. Traditional indicators such as thermal-tolerant and total coliforms performed poorly as fecal indicators, as their presence was not indicative of litter application. Antibiotic resistance for enterococci demonstrated increased resistance to polymixin b and select aminoglyocosides; however, the majority of isolates were not resistant to more than two antibiotic classes. The majority of staphylococci, which make up the majority of culturable litter-borne bacteria (>108 g-1), were susceptible to most drugs tested. This study demonstrated that poultry litter application can lead to microbial runoff following simulated rain events, and that future studies should focus on the use of staphylococci, enterococci, and C. perfringens as indicators of this phenomenon.