Tuesday, November 3, 2009
Convention Center, Exhibit Hall BC, Second Floor
Effluent from swine manure treatment lagoons is a valuable byproduct of confined feeding operations. In the Mid-South US, effluent is used as fertilizer for grass hay in spray-irrigated fields. Recent work documented levels of nutrients and fecal bacteria, including human pathogens, in lagoons in the region, but little is known of bacterial survival in soil. Objectives of the present study were to determine and compare the presence and levels of selected fecal and pathogenic bacteria in soils inside and outside spray fields and to measure concurrent nutrient levels. Fields that had received effluent for >10 yr were studied. Soil cores were collected from a contiguous soil type inside and outside a spray field. Twenty soil types were sampled (four each at five locations, representing 17 sow farm lagoons) in February and March 2009 before the April to September irrigation season. Soil cores 0-5 cm and 5-10 cm deep were analyzed for bacteria and adjacent (<10 cm) cores 0-15 cm deep were analyzed for nutrients. Five core samples collected at 10 to 20-m intervals were composited to comprise each bacterial and nutrient 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. Analyses showed higher bacterial levels inside than outside spray fields for heterotrophic plate counts, thermotolerant coliforms, Staphylococcus aureus and Clostridium perfringens. Levels of Escherichia coli and Enterococcus spp. did not differ inside and outside. Tests for the presence of Listeria spp. showed no significant difference in incidence of positive samples (23% inside and 28% outside). Tests for Campylobacter spp. and Salmonella spp. were negative, suggesting that these enteric pathogens either do not survive in spray field soils or survive at low levels below detection limits.