ARS | Publication request: Comparison of selected nutrients and bacteria from common contiguous soils inside and outside swine lagoon effluent spray fields after long-term use

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 18, 2010
Publication Date: August 1, 2010
Repository URL: http://doi:10.2134/jeq2009.0447
Citation: McLaughlin, M.R., Brooks, J.P., Adeli, A., Read, J.J. 2010. Comparison of selected nutrients and bacteria from common contiguous soils inside and outside swine lagoon effluent spray fields after long-term use. Journal of Environmental Quality. 39:1829-1840.

Interpretive Summary: This study documented the amounts of selected nutrients, fecal bacteria and bacterial pathogens in soils after more than 15 years of swine lagoon effluent applications. This is the first report to document levels of fecal and pathogenic bacteria in soils of long-term spray fields in the Mid-South region of the US. The findings suggest that swine manure management plans in the region have been effective and appropriate. Levels of the bacterial pathogens Campylobacter spp., Listeria spp. and Salmonella spp. found in spray field soils were relatively low and did not differ from background levels found outside the spray fields. In fact, Campylobacter spp. and Salmonella spp. could not be cultured from any soil samples, although molecular tests confirmed the presence of DNA for both, indicating that both were or had been present, as was expected based on an earlier and separate study of lagoon effluents. We conclude from the present and earlier work that the bacterial pathogen load transported to spray field soils during the 2008 irrigation season was relatively low, declined by natural die off during the winter and reached background levels before the 2009 irrigation season. Results of the present study showed no evidence of cumulative buildup of bacterial pathogens in spray field soils. Risk assessment models for bacterial pathogen contamination from land application of swine lagoon effluents have not been developed, and although low pathogen levels found in the present study are encouraging, more research on temporal distribution of pathogens and new models are needed to fully assess potential risks.

Technical Abstract: Swine (Sus scrofa domestica) lagoon effluent is a valuable fertilizer. In the Mid-South US it is applied to grass hay in spray-irrigated fields from April to September. Lagoon levels of nutrients and bacteria, and soil levels of nutrients, were known, but little was known of effluent bacterial levels in soil. The present study determined and compared the presence and levels of effluent bacteria, including human pathogens, and nutrients in soils inside and outside spray fields after >15 yr of effluent fertilization. Four soils were sampled at each of five locations in February and March 2009. Cores (0 to 5 cm and 5 to 10 cm deep) were tested for bacteria. Adjacent (<10 cm) cores (0 to15 cm deep) were tested for nutrients. Five cores collected at 15 m intervals were combined to comprise each sample. Analyses showed higher pH and Mehlich-3-extracable (M3-) P, Mg, K, Na, Cu and Zn inside than outside spray fields, while total N, total C, M3-Ca and M3-Mn did not differ. Levels for heterotrophic plate counts, thermotolerant coliforms, Staphylococcus spp. and Clostridium perfringens (Veillon and Zuber) Hauduroy et al. were higher inside than outside spray fields, but Escherichia coli (Migula) Castellani and Chalmers and Enterococcus spp. were not. Cultural presence/absence tests for Listeria spp., Campylobacter spp. and Salmonella spp. detected only Listeria spp. (23% of samples inside and 28% outside), while molecular tests detected all three at low levels that were not different inside and outside spray fields. The pathogens occur naturally outside the spray field, while those from effluent do not survive or survive at low levels inside spray fields.