Abstract
Biological soil amendments of animal origin (BSAAOs), including untreated (e.g., raw or aged manure, or incompletely composted manure) and treated animal products (e.g., compost), are used for crop production and as part of soil health management. Application of BSAAO's must be done cautiously, as raw manure commonly contains enteric foodborne pathogens that can potentially contaminate edible produce that may be consumed without cooking. USDA National Organic Program (NOP) certified production systems follow the 90-or 120-day interval standards between applications of untreated BSAAOs and crop harvest, depending on whether the edible portions of the crops are in indirect or direct contact with the soil, respectively. This study was conducted to evaluate the survival of four foodborne pathogens in soils amended with BSAAOs and to examine the potential for bacterial transfer to fresh produce harvested from USDA NOP certified organic farms (19) from four states. Only 0.4% (2/527) of produce samples were positive for L. monocytogenes. Among the untreated manure and compost samples, 18.0% (42/233) were positive for at least one of the tested and culturable bacterial foodborne pathogens. The prevalence of non-O157 STEC and Salmonella in untreated manure was substantially > that of E. coli O157:H7 and L. monocytogenes. Of the 2,461 soil samples analyzed in this study, 12.9% (318) were positive for at least one pathogen. In soil amended with untreated manure, the prevalence of non-O157 STEC [7.7% (190) and L. monocytogenes (5.0% (122), was > that of Salmonella (1.1% (26)] or E. coli O157 [0.04% (1)]. Foodborne pathogen prevalence in the soil peaked after manure application and decreased significantly 30 days post-application (dpa). However, non-O157 STEC and L. monocytogenes were recovered from soil samples after 90 and 120 dpa. Results indicate that produce contamination by tested foodborne pathogens was infrequent, but these data should not be generalized outside of the specific wait-time regulations for organic crop production and the farms studied. Moreover, other sources of contamination, e.g., irrigation, wildlife, environmental conditions, cropping and management practices, should be considered. This study also provides multi-regional baseline data relating to current NOP application intervals and development of potential risk mitigation strategies to reduce pathogen persistence in soils amended with BSAAOs. These findings contribute to filling critical data gaps concerning occurrence of fecal pathogens in NOP-certified farming systems used for production of fresh produce in different US regions.
Highlights
Healthy fertile soils are essential for resilient crop production and supporting the global ecosystem
Few studies have reported the survival of Salmonella spp. and non-O157 STEC in soil amended with untreated manure under natural conditions, and most of those were in conventionally managed fields (Gu et al, 2018, 2019; Sheng et al, 2019)
Non-O157 STEC and L. monocytogenes positive soil samples were identified after 90-and 120-days post-manure application and incorporation
Summary
Healthy fertile soils are essential for resilient crop production and supporting the global ecosystem They positively contribute to soil water retention, support a diversity of organisms vital to decomposition and nutrient cycling, provide crops with essential nutrients, and can maintain carbon stores, contributing to global climate change mitigation. Biological soil amendments of animal origin (BSAAOs) are especially popular because of their high nutrient content and low cost. They can improve several soil characteristics, including available nutrients, water retention, permeability, water infiltration, drainage, aeration, and structure (Rosen and Bierman, 2005; Rosen and Allan, 2007; Sharma and Reynnells, 2016), and are a valuable component of sustainable farming. The use of BSAAOs in organic production provides a means of beneficial use manure from livestock premises (Rosen and Allan, 2007; Sharma and Reynnells, 2016)
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