Assessment of current practices of organic farmers regarding biological soil amendments of animal origin in a multi-regional US study

Authors: PIRES, ALDA - University Of California, Davis; Millner, Patricia; BARON, JEROME - University Of California, Davis; JAY-RUSSELL, MICHELE - University Of California, Davis

Submitted to: Food Protection Trends
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2018
Publication Date: 9/1/2018
Citation: Pires, A., Millner, P.D., Baron, J., Jay-Russell, M. 2018. Assessment of current practices of organic farmers regarding biological soil amendments of animal origin in a multi-regional US study. Food Protection Trends. 38:347-362.

Interpretive Summary: Many crop-based agricultural operations utilize biological soil amendments of animal origin (BSAAOs) to maintain soil health and provide crop nutrients. These amendments are particularly important to certified organic farmers because USDA’s National Organic Program (NOP) prohibits the use of synthetic chemical fertilizers. Application of partially, incompletely composted, uncomposted, and/or untreated animal manure (hereafter called “raw manure”), may introduce foodborne pathogens, including E. coli O157:H7, Salmonella spp., Campylobacter spp., Listeria and Cryptosporidium parvum, to fresh produce typically consumed raw (without cooking). Data are needed to conduct food safety risk assessments regarding current practices related to the use of soil amendments in organic farming and to assess use of current NOP practices requiring 90 or 120 day manure application to crop harvest wait times. This study was conducted to characterize the use of BSAAOs, including rotational grazing and composting, in organic and sustainable agriculture with a focus on produce (e.g., vegetables, nuts and fruits) commodities covered under the Produce Safety Rule. Results show that 89% of the 666 respondents produced fresh produce commodities, with 82% certified organic and operators of relatively small to medium size farms. Fifty-eight percent of the respondents reported using raw manure, and BSAAOs were used by 46.8% of producers growing produce typically consumed without cooking. Among respondents using raw manure in fresh produce fields, more than 90% responded that they wait either 90 or 120 days post-application of untreated manure before crop harvest. This study revealed multiple factors associated with on-farm manure management practices vary regionally and by state across the USA. These factors may affect survival and persistence of pathogens in manure-amended soils. Some farmers use the terms treatment, composting and aging as equivalent processes for aged, stacked animal manures. Important training and education needs were identified related to the specific methods required to produce manure compost compliant with the Produce Safety Rule. Mitigation practices to decrease the risk of potential microbial contamination from raw manure to fresh produce need to account for multiple factors across different regions in the US. Results of this study will aid extension specialists, farm certifiers, fresh produce farm operators in developing risk mitigation strategies and good agricultural practices to reduce microbial contamination of fresh produce in systems using BSAAOs, especially untreated manure.

Technical Abstract: Certified organic producers use biological soil amendments of animal origin (BSAAOs) to improve soil fertility and quality. The prevention of microbial contamination of crops has been based on time-interval criteria between the application and crop harvesting. The objective of this study was to assess current practices related to the use of BSAAOs and food safety risks in organic agriculture with a focus on produce commodities covered under the Produce Safety Rule. A total of 666 producers completed the survey (571 online and 95 hardcopy), and 89.2% (594/666) of the respondents produced fresh produce. Eighty-two percent of the producers were certified organic and represent relatively small-medium size farms. BSAAOs were applied by 46.8% of producers growing produce that is typically consumed fresh. Fifty-eight percent of the farmers reported the use of raw manure. This survey showed that multiple factors related to on-farm manure management practices, which may affect directly survival and persistence of pathogens in manure-amended soils, vary by region and by state in the USA. Thus, mitigation practices to decrease the risk of potential microbial contamination to fresh produce resulting from application of untreated manure must take into account multiple factors across different regions. This survey provides a framework for risk mitigation strategies to reduce microbial contamination of fresh produce in systems using BSAAOs, mainly untreated manure in organic agriculture.