What Is a Soil Amendment?
Soil amendments are any agents, whether chemical, biological, or physical, purposefully added to soil to improve plant growth and development. Commonly used soil amendments include elemental fertilizers, compost, manure, animal byproducts, peat moss, perlite, pre-consumer vegetative waste, sewage sludge biosolids, table waste, agricultural tea, and yard trimmings. Biological soil amendments refer to any amendments containing biological materials, and biological soil amendments of animal origin refer to any amendments consisting of, whether in whole or in part, of materials of animal origin. These terms are defined under the Food Safety Modernization Act § 112.3(c).
Treated soil amendments are defined as having been processed to reduce the presence of microorganisms, or consisting of biological materials which have been processed to reduce the presence of microorganisms. Untreated biological soil amendments of animal origin are any biological amendments which: have not been processed, have become contaminated after treatment, have been recombined with another untreated amendment, is/contains untreated waste, or is an agricultural tea that contains an agricultural tea additive. An additive is a nutrient source meant to increase microbial biomass. Compliance for these processes is defined under § 112.54 and § 112.54 of FSMA.
What Are the Risks of Soil Amendments?
The major risk posed by soil amendments is from those that contain manure or other untreated components. Chemical/synthetic fertilizers usually do not come with these risks because they either cannot sustain pathogens or are processed safely. Still, there have been scarce but dangerous outbreaks of Salmonella associated with unsafe chemical/synthetic fertilizers. Untreated human waste is not allowed as a soil amendment, unless it is a biosolid treated under the standards of 40 CFR part 503. Biosolids are still at a high risk of transmitting pathogens or containing high levels of heavy metals and pharmaceuticals. Pre-consumer vegetative waste, or solid waste that is completely vegetative in origin and not involved in other activities, such as commercial use, may contain chemical hazards, especially pesticides or physical hazards such as glass.
Given its prevalence on farms, manure is a useful resource as a soil amendment to improve many of its aspects. While there are food safety risks associated with its use, these risks may still be minimized through careful and appropriate utilization. Raw manures represent a major microbial risk because they tend to be filled with pathogens of all types, especially pathogens communicable to humans. Any product, including manure, used as a soil amendment, that is raw or incompletely treated, is a higher risk amendment. If treated and untreated amendments are mixed, both must be regarded as untreated.
How Can the Risks of Soil Amendments Be Reduced?
Good Agricultural Practices (GAPs) are beneficial in many ways for sanitary farms, and they also reduce the risk of soil amendments. These practices could include: selecting only treated soil amendments, extending the application to harvest intervals, ensuring that runoff does not take place, reducing cross-contamination to equipment, and recordkeeping to monitor soil amendment application and treatment.
Composting is one way to create well-treated soil amendments. Under § 112.3(c), it is a controlled process under which organic material decomposes for a designated time period and at a high temperature. Both factors will depend on many potential variables, but § 112.55 outlines that the static process should take place for at least 3 days and at 131 degrees Fahrenheit or more. There are other scientifically valid methods outlined within FSMA, so long as they meet microbial standards.
Another risk reduction strategy is to apply amendments in field rotations where no produce is growing. Since pathogens live for a long time, maximizing time between application of manure, or other amendment, is a good way to minimize risk. Application should always attempt to avoid the harvestable parts of produce as well as covered produce after application, and it is important to be aware of potential spread into adjacent fields that could be contaminated. To prevent this runoff, it is recommended not to spread in high winds or on frozen/saturated grounds. Buffer zones are also useful to prevent cross-contamination.
While the FDA currently has no standards for appropriate application intervals when it comes to untreated soil amendments, it is likely that they will create such a policy in the future. In the meantime, there is still risk in intervals that are too short. The National Organic Program recommends that raw animal manure needs to be composted unless it is used as an amendment not less than 120 days before harvest with produce where edible components have soil contact, and not less than 90 days otherwise.
Cross-contamination with equipment is an additional danger. Standard Operating Procedures are the primary method by which farms should create sanitary conditions. General farm traffic should be averted from areas related to soil amendments, and equipment/tools must be installed and maintained for proper cleaning. All contact surfaces must be cleaned to protect against contamination making its way to produce, and loading equipment should be used so that contamination is minimized. The latter three policies are under § 112.123 of FSMA.
Under § 112.52, biological soil amendments of animal origin must be handled so that they do not become a potential contamination source. Such amendments which are treated must be handled to minimize the risk of contamination with untreated amendments. Examples of ways to achieve this include covering compost piles, isolating them from raw manure piles, keeping animals away from compost piles, and storing soil amendments away from areas at a high risk of cross-contamination.
Additionally, workers should be well-trained in understanding the risks of soil amendments and how to minimize these risks. Employers need to provide appropriate resources, such as proper clothing, so that workers can do their jobs in sanitary conditions. To document that these policies are rigorously followed, record-keeping is critical. Under § 112.163, existing records for other compliance standards need not be duplicated if they contain necessary information, such as what types of amendments are applied, when they are applied, how much was applied, and the results of any analysis or testing done. Record-keeping also needs to entail process controls for composting or treating amendments. For all requirements related to biological soil amendments of animal origin, look to § 112.60. Corrective action plans to outline steps in case of misused amendments, even if simple, are recommended to get ahead of a food safety risk.