Composts awaiting incorporation into crop land. Photo by F. Michel.

New program supports the use of composts as a conservation practice

By Frederick Michel, Jr.

Farmers have known for centuries, and research has demonstrated, that composts can provide multiple benefits to crop, pasture and forest soils. These include providing slow-release nutrients, increasing plant growth and health, enlivening soil microbial communities, increasing soil carbon content, aggregation and water holding capacity, and sequestering carbon to help reduce climate change. The composting process itself redirects valuable plant nutrients and carbon in organic wastes from landfilling, where they degrade anaerobically and emit powerful greenhouse gases like methane. These benefits fall well within the mission of the U.S. Natural Resources Conservation Service (NRCS), USDA’s primary conservation agency, to “deliver conservation solutions so agricultural producers can protect natural resources and feed a growing world.”

In 2018, the NRCS introduced a new Interim Conservation Practice Standard called the Soil Carbon Amendment, that proposed guidelines for the application of compost, biochar and other organic materials. The purpose of the program is to improve or maintain soil organic matter, sequester carbon and enhance soil carbon (C) stocks, improve soil aggregate stability and improve habitat for soil organisms, all properties that composts provide.

In 2022 this standard was adopted as a Conservation Practice for Soil Carbon Amendment, under Code 336. As part of this program, incentives to use compost and other organic amendments will be provided through programs such as the Environmental Quality Incentives Program (EQIP), Conservation Innovation Grants, and the Conservation Stewardship Program. The incentives would include support for purchasing, transporting, and applying composts and other carbon amendments.

To participate in the program, soil properties such as C:N ratio and Phosphorus availability must first be measured to determine whether a carbon amendment can provide the desired benefits. Once this has been established, composts must be sourced and tested using standard methods such as the US Composting Council’s Seal of Testing Assurance Program (STA) or State-approved certification programs so that properties and the availability of nutrients can be used in soil carbon amendment plans. Compost producers must document the origin of the compost, assure that it was made using a biological, aerobic process and has been tested for soil nutrients plus microbial pathogens before it can be used in the program.

Some issues need to be addressed before implementation. One is the variable nature of compost products and the extent to which they can provide these benefits. For example, different types of compost (yard trimmings, food scraps, manure or biosolids) provide different amounts of N, P and K and at different rates. Some composts are unbalanced fertility sources requiring nitrogen amendment to allow crops to reach full yield. Other organic sources like biochar provide no nutrients and are biologically inactive, but may introduce recalcitrant carbon that persists longer than the carbon provided by composts and improve cation exchange capacity. Other organics like liquid manure are already widely used and how they may fit into the program is unclear. To validate the benefits, soil testing after 1-3 years is needed.

Another issue is the availability of composts in the state. To help increase the supply of composts and reduce the negative impacts of landfilling food waste and other organic materials, the Ohio EPA and USDA have been supporting the development of composting infrastructure in Ohio. Information about sources of compost that could be used will be available from the Ohio Organics Council (OHOC), a non-profit membership organization of composting facilities, haulers, educators, researchers and consultants. Guidelines and training of Technical Service Providers to address these and other issues, understand how to use carbon amendments, and identify which will qualify for the program, are under development by NRCS.

Overall, Code 336 will allow farmers to reduce their reliance on expensive non-renewable fertility sources and help meet the growing desire to move toward regenerative agricultural practices that improve soil health, recycle nutrients and sequester carbon. For more information contact your NRCS agent or the Ohio Composting and Manure Management program at wicks.14@osu.edu.

Frederick Michel is a Professor of Biosystems Engineering in the Department of Food, Agricultural and Biological Engineering, Ohio State University-OARDC, michel.36@osu.edu.

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