Soil Carbon Amendments

May 20, 2024

This blog summarizes USDA Natural Resources Conservation Service (NRCS) Code 336, which addresses Soil Carbon Amendments as a Conservation Practice Standard, part of the USDA Environmental Quality Incentives Program (EQIP), which provides monetary incentives to improve, among other things, soil quality. Soil carbon amendments include compost, biochar, and other carbon-based materials.

The program is potentially beneficial to compost and biochar facilities (public or private) as the USDA payments include an amount for purchasing finished compost or biochar, which would provide revenue to the facility owner. The payment schedules vary by state. For example, Delaware’s material purchase rates are $26.10 per CY for compost and $201.87 per CY for biochar.

Short History of the Amendments

Introduced in December 2019, Code 808 is an interim standard with the purposes of:

1. Maintain, increase, or improve soil organic matter quantity and quality
2. Maintain or improve soil aggregate stability
3. Maintain or improve habitat for soil organisms
4. Improve plant productivity and health
5. Improve the efficient use of irrigation water

It lists suitable criteria for applicable amendments and guidance for planning a carbon soil amendment. Twenty-nine states adopted code 808.

Code 336 was introduced in November 2022 as the final standard for soil carbon amendments, with minor changes from Code 808. Its purposes are to:

1. Improve or maintain soil organic matter.
2. Sequester carbon and enhance soil carbon (C) stocks.
3. Improve soil aggregate stability.
4. Improve habitat for soil organisms.

The main changes that Code 336 implements are quality standards for evaluating soil for amendment and the carbon amendments that need application to the soil.

Eligible Areas

Areas to which this practice applies, if organic carbon amendments will improve soil conditions:

1. Crop
2. Pasture
3. Range
4. Forest
5. Associated Agriculture Lands
6. Developed Land
7. Farmstead

Landowners or operators are responsible for planning, designing, and implementing carbon amendment applications, including acquiring all permits or approvals. The application and approval process varies by state and may be subject to local regulations.

Soil Criteria

Per Code 336, before carbon amendment application, evaluate all soil for:

1. Soil pH
2. Soil texture
3. Soil organic matter or soil organic carbon
4. Extractable phosphorous, potassium, calcium, sulfur, and magnesium
5. Cation exchange capacity

When conservation objectives are required, evaluate the soil for:

1. Aluminum, sodium, and soluble salts (electrical conductivity)
2. Bulk density
3. Aggregate stability
4. Available water capacity
5. Iron, manganese, copper, zinc

Soil Carbon Amendments Criteria

Code 808 Compost Requirements:

1. Carbon to Nitrogen ratio between 15:1 and 30:1 (target 20:1)
2. 40-60% moisture (60-40% solids)
3. Analysis of carbon and nitrogen content, phosphorus, potassium, pH, soluble salts (electroconductivity), organic matter, and bulk density

Code 336 Compost Requirements:

1. Document the origin of the compost
2. Report and meet conditions for All Carbon Amendments in Table 1
3. Report and meet conditions for Compost Amendments in Table 2

Code 336 Biochar Requirements:

1. Document the origin and production method
2. Report and meet conditions for All Carbon Amendments in Table 1
3. Report and meet conditions for Biochar Amendments in Table 3

Produced compost should be by controlled aerobic, biological decomposition of biodegradable feedstocks and should have the US Composting Council’s Seal of Testing Assurance Program (STA) or meet the Table 2 criteria.

Compost can be combined with other regionally appropriate soil carbon amendments, such as biochar, wood chips, sawdust, or pulverized paper, to meet the soil’s specific needs. Identify contaminants by testing any soil amendments. Remove contaminants such as glass, metal fragments, film plastic, hard plastic, and sharps before submitting the compost application.

Produce biochar by heating biomass to a temperature above 350 °C under controlled and limited oxygen concentrations to prevent combustion (i.e., pyrolysis or gasification). It should have the International Biochar Initiative (IBI) Certified biochar seal or meet the criteria in Table 3.

Payment Rate Tables (CT, DE, and FL Examples)

HU = “Historically Underserved” Farmers and Ranchers

Find additional state payment tables at https://www.nrcs.usda.gov/getting-assistance/payment-schedules.

Code 336 Implementation

Not all state offices have adopted NRCS Code 336, but the figure below by the US Biochar Initiative shows adoption at the close of 2023. (https://biochar-us.org/code336).

Discussion of the state-by-state adoption of NRCS Code 336 is in the BioCycle article States Should Adopt NRCS Soil Conservation Standard Code.

Code 336 pricing for compost appears to provide reasonable funding to offset material purchase, transport, application, and technical services. However, Code 336 pricing for biochar does not provide enough funds to subsidize the purchase of biochar in most markets fully. Further, additional costs remain for biochar transport, application, or technical services.

Table 1. Soil requirements under NRCS Code 336 (2022).

Table 2. Compost requirements under NRCS Code 336 (2022).

Table 3. Parameters for Biochar Amendments

Additional Resources:

• As always, contact the Organics Management team at SCS Engineers if you have questions pertaining to your specific facility.
• Meeting Evolving Air Quality Regulations and Permit Requirements for Composting Facilities
• Diversify Waste Management Revenue By Maximizing Carbon Credit Opportunities
• Organics Diversion – Find a Grant Program
• Organics Management