United States Department of Agriculture 336-CPS-1

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NRCS reviews and periodically updates conservation practice standards. To obtain the current 

version of this standard, contact your Natural Resources Conservation Service State office or 

visit the Field Office Technical Guide online by going to the NRCS website at 

https://www.nrcs.usda.gov/ and type FOTG in the search field. 

USDA is an equal opportunity provider, employer, and lender.

Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

SOIL CARBON AMENDMENT 

CODE 336 

(ac)

DEFINITION 

Application of carbon-based amendments derived from plant materials or treated animal byproducts. 

PURPOSE 

Use this practice to accomplish one or more of the following purposes: 

• Improve or maintain soil organic matter. 

• Sequester carbon and enhance soil carbon (C) stocks. 

• Improve soil aggregate stability. 

• Improve habitat for soil organisms. 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies to areas of Crop, Pasture, Range, Forest, Associated Agriculture Lands, Developed

Land, and Farmstead where organic carbon amendment applications will improve soil conditions. 

CRITERIA 

General Criteria Applicable to All Purposes 

Plan, design, and implement carbon amendment applications in compliance with all Federal, State, and

local laws and regulations. The owner or operator is responsible for securing all required permits or

approvals and for applying in amendment in accordance with such laws and regulations. 

Evaluate site using appropriate planning criteria, assessment tools, or evaluation activities for the intended

land use to determine where soil carbon amendments will achieve the intended purpose(s). 

Test the soil prior to amendment application. Use laboratories meeting current requirements and

performance standards of the North American Proficiency Testing Program under the auspices of the Soil

Science Society of America or use an alternative State-approved certification program that considers

laboratory performance and proficiency to ensure accuracy of soil test results. 

Follow Land Grant University (LGU) or industry guidance to collect, prepare, store and ship soil samples.

Ensure sampling protocol and laboratory soil test methods are the same as those required by the Stateadapted NRCS Conservation Practice Standard (CPS) Nutrient Management (Code 590). 

At a minimum, measure the following soil properties: 

• Soil pH. 

• Soil texture. 

• Soil organic matter or soil organic carbon. 
• Extractable phosphorus, potassium, calcium, sulfur, and magnesium. 

• Cation exchange capacity. 

Test for any of the following properties when applicable to local conditions or conservation objectives: 

• Aluminum, sodium, and soluble salts (electrical conductivity). 

• Bulk density. 

• Aggregate stability. 

• Available water capacity. 

• Iron, manganese, copper, zinc. 

Additional Criteria for All Amendments 

Prior to application, document the physical and chemical analysis (i.e., composition and properties) of

amendment per amendment category near the time of application. Current amendment analysis

documentation shall be provided by the party who produces the amendment. 

Apply carbon amendments with minimal disturbance at a rate and time that will achieve the intended

purpose. 

Evaluate the landscape, soil properties, amendment composition, plant nutrient needs, and application

rate to determine if NRCS CPS Nutrient Management (Code 590) is needed to address nutrient-related

resource concerns. 

Do not apply high-salt materials (>8 mmhos/cm) where salinity is a concern. 

Do not apply amendments: 

• Produced from crop residues that could otherwise provide soil protection and improve soil health

(e.g., stover or straw) or from woody residue that is necessary to sustain forest health and support

wildlife habitat as referenced in NRCS CPS Forest Stand Improvement (Code 666). 

• During high wind events. 

• Where soil, site, climate, or condition pose a significant risk of loss due to slope, runoff potential,

rainfall or irrigation intensity, or other factors. 

• To areas where negative impacts on air or water resources or nutrient cycling may occur. 

• That may contain undesirable plant propagules or seeds. 

• Where changes to the plant community could be undesirable or unknown (e.g., changing a native

or an established desired community etc.). 

• When nutrients in the amendment will not be directly used (e.g., nutrient-rich amendment

applications to fallow land or fields without existing or planned vegetative cover). 

• Such as raw manure or biosolids. When applying soil amendments such as raw manure and

biosolids refer to NRCS Conservation Practice Standard Nutrient Management (Code 590). 

For operations certified under USDA’s National Organic Program (NOP), apply and manage amendments

according to program regulations, including but not limited to compost temperature and carbon to nitrogen

ratio (C:N) requirements under 7 CFR §205.203. Operators should consult their certifying agent to ensure

compliance with NOP standards (or other certification programs or marketing agreements) prior to

application. 

Evaluate the cumulative impacts of critical amendment components such as nutrients, nutrient

interactions, toxicants, or contaminants when planning repeat applications. Include a monitoring plan as

appropriate based on risk. 

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When feedstocks have higher risk of synthetic organic or heavy metal contaminants, evaluate amendment

as appropriate for contaminant and amendment type (e.g., processed municipal waste feedstocks that

may contain pesticide residues, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl’s

(PCBs), and polyfluoroalkyl substances (PFAS), etc.). 

Report values for all parameters listed in table 1. Identify any parameter that may limit the application of

amendments. Do not apply amendments if the maximum allowable levels listed are exceeded. 

 

Table 1. Parameters for All Carbon Amendments 

Compost 

Use compost that is produced by the controlled aerobic, biological decomposition of biodegradable

feedstocks. Use compost with the US Composting Council’s Seal of Testing Assurance Program (STA) or

that meets the following criteria in Table 2 below as determined by the Test Methods for the Examination

of Composting and Compost (TMECC) or by LGU recognized methods. 

Document: 

• Origin of compost. 

• Parameters for All Carbon Amendments in table 1. 

Parameter Range Unit

Feedstock Report1 Type by %

pH Report pH units

Electrical Conductivity (EC) Report dS/m

Moisture Report %

Organic Matter/Carbon Report % DW2

Total Nitrogen Report % DW

Particle Size Report % per size class

Phosphorus Report mg/kg4 DW

Potassium Report mg/kg DW

Calcium Report mg/kg DW

Magnesium Report mg/kg DW

Arsenic3 <41 mg/kg DW

Cadmium <39 mg/kg DW

Copper <1500 mg/kg DW

Lead <300 mg/kg DW

Mercury <17 mg/kg DW

Nickel <420 mg/kg DW

Selenium <100 mg/kg DW

Zinc <2800 mg/kg DW

1Report results, also see criteria under amendment type. 

2DW = Dry weight. 

3Pollutant concentration limit values from US EPA Title 40 Part 503 STANDARDS FOR THE USE OR

DISPOSAL OF SEWAGE SLUDGE. Follow State and local laws and regulations. 

4milligrams per kilogram (mg/kg) = parts per million (ppm) = grams per ton (g t-1)

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• Parameters for Compost Amendments in table 2. 

Table 2. Parameters for Compost Amendments 

Use laboratories successfully meeting the current requirements and performance standards of the STA or

use an alternative State-approved certification program that considers laboratory performance and

proficiency to ensure accuracy of laboratory analyses. 

Ensure compost is screened as necessary to remove contaminants such as glass, metal fragments, film

plastic, hard plastic, and sharps. 

Do not apply compost when a phosphorus risk assessment indicates a high or very high risk for

phosphorus transport. Consider manufactured compost products that are low in soluble phosphorous. 

Ensure mitigating conservation practices to prevent runoff are in place at the time of application if compost

is spread on slopes greater than 8% and within 100 feet of a surface water body. Do not apply soil

carbon amendments on slopes greater than 15%. 

Do not apply soil carbon amendments to rangelands except where it is facilitating CPS Range Planting

(Code 550) or CPS Critical Area Planting (Code 342). 

Biochar 

Use biochar that is produced by heating biomass to a temperature in excess of 350 °C under conditions of

controlled and limited oxygen concentrations to prevent combustion (i.e., pyrolysis or gasification). Use

biochar with the International Biochar Initiative (IBI) Certified biochar seal or that meets the criteria in table

3 as determined by the methods in IBI Standards (version 2.1), or by LGU recognized methods. 

Document: 

• Origin of biochar and production method (e.g., verification of temperature and limited oxygen

conditions). 

• Parameters for All Carbon Amendments in table 1. 

• Parameters for Biochar Amendments in table 3. 

 

Table 3. Parameters for Biochar Amendments 

Parameter Range Unit

C:N Report1 unitless

Organic matter Report % DW

Fecal coliform <1000 MPN2 per g dry compost

Salmonella spp. <3 MPN per 4 g dry compost

1Report = Required results only, no threshold or range needs to be met. 

2MPN = Most Probable Number.

Parameter Range Unit

Total Ash Report1 % of total mass, dry basis

Liming equivalent Report % CaCO3

Organic Carbon (Corg) >10 % DW

H:Corg <0.7 Molar ratio

Chromium <1200 mg per kg DW

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Use laboratories successfully meeting the current requirements and performance standards of the IBI

Seal or use an alternative State-approved certification program that considers laboratory performance and

proficiency to ensure accuracy of laboratory analyses. 

Apply biochar under weather conditions using application methods that reduce risk of off-site movement

and follow worker safety precautions, including use of appropriate Personal Protective Equipment (PPE). 

Other carbon amendments 

Use regionally-appropriate carbon-based materials to fulfill the purpose(s). Other carbon amendments

may include but are not limited to waste plant materials that would otherwise not provide a conservation

benefit (e.g., harvested invasive aquatic species), wood chips, pulverized paper, bagasse, or distillation

residue. 

Follow State specific criteria for regionally appropriate carbon-based materials. 

CONSIDERATIONS 

General Considerations 

Add mature, stable compost (i.e., based on maturity index, respirometry, or documented time and

temperature of composting process) that will increase soil biological activity and diversity to enhance root

health and promote resistance to pathogenic organisms. 

Apply low H:Corg biochar (<0.7) to maximize soil carbon sequestration. 

Inoculate biochar with compost, compost tea, or manure to balance nutrients and nutrient interactions,

stabilize pH, and improve amendment moisture content to aid application. Determine if NRCS CPS

Nutrient Management (Code 590) is needed to address nutrient-related resource concerns. 

Adjust nutrient management and pest management plans as needed for the specific amendment type and

purpose. 

• Compost or other amendments with C:N greater than 30:1 can immobilize nutrients, especially

nitrogen, and may necessitate supplemental nitrogen applications for plant growth. 

• The targeted C:N ratio for compost or other amendments is 20:1. C:N ratios below 15:1 are likely to

mineralize N and should be used at a time when plant N demand will prevent N loss. 

• Biochar with high adsorptive capacity can reduce the effectiveness of some pesticides. 

Time operations to minimize potential soil compaction and evaluate traffic routes to prevent erosion.

Consider coordinating amendment applications with other operations to minimize traffic (e.g., seed and

apply compost at the same time). Disturbed areas should be appropriately treated to minimize potential

erosion. 

Consider potential contamination pathways to crops typically consumed raw, water distribution systems,

etc. when applying amendments that may contain pathogens (e.g., biological soil amendments of animal

origin including composted manure, composted carcasses; reference the Food and Drug Administration’s

Food Safety Modernization Act at www.fda.gov/FSMA). 

Reduce risk of off-site movement or spontaneous ignition by properly storing and handling amendments.

When staging materials for application, locate piles where they will not increase risk of material or

leachate loss to sensitive areas. 

1Report = Required results only, no threshold or range needs to be met

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Considerations to Maintain or Improve Soil Organic Matter and Sequester Carbon 

When applying soil carbon amendment with diesel-powered equipment and vehicles, consider using Tier 3

or Tier 4 emissions certified diesel engines to minimize nitrous oxides and particulate matter emissions

from diesel exhaust and to maximize climate benefits. 

Consider life cycle analysis of the amendment that evaluates the feedstock source, processing and

transportation impacts on carbon and greenhouse gas accounting. 

Consider using COMET-Farm or COMET-Planner to estimate changes in carbon and greenhouse gas

emissions of planned practices. 

On cropland, soil organic carbon is related to the volume of soil disturbed, intensity of the disturbance, soil

moisture content, and soil temperature at the time the disturbance occurs. Make this practice most

effective at increasing soil organic carbon stocks, improving soil health and reducing carbon loss: 

• Perform any deep soil disturbance, such as ripping, subsoiling, or fertilizer injection, so the vertical

slot created by the implements is closed at the surface. 

• Perform soil disturbance at a time when exposed soil carbon is less likely to be oxidized and lost as

CO2 (e.g., when soil temperatures are below 50o F or when soil is not excessively wet or

excessively dry). 

PLANS AND SPECIFICATIONS 

In the soil carbon amendment plan, include: 

• Purpose of practice. 

• Assessment of soil health resource concerns using State-approved tools for the appropriate land

use. 

• Results of laboratory soil health tests that include, at a minimum soil organic matter or soil organic

carbon and include other soil health properties based on the purpose(s) and resource concern(s) to

be addressed. 

• Map and site description of conservation management units receiving amendments (e.g., crop

rotation, native vegetation, etc.). 

• Aerial photos that include locations of sensitive areas and setbacks, as applicable. 

• Soil survey map of the site. 

• Soil information including but not limited to soil type, surface texture, slope, runoff class, drainage

class, flooding and ponding frequency and duration, or soil interpretations designed for general land

use planning which provide dynamic soil property information and/or soil health response to carbon

amendments (i.e., Dynamic Soil Properties Response to Biochar found in Web Soil Survey under

Suitabilities and Limitations tab). 

• Plant information including but not limited to existing, invasive, noxious, rare, or wetland plant

species as noted in the PLANTS database, as applicable. 

• Complete amendment analysis (See General Criteria for each amendment type). 

• Application rate, method, timing, and when applicable, method of incorporation. 

• Monitoring plan for amendment effectiveness for the planned purpose(s) using appropriate

monitoring activities. Include a soil organic matter or soil organic carbon test to determine the

effectiveness of the application for improving soil health and soil organic carbon 1 to 3 years after

application. Soil testing at least 3 years or more after application may monitor longer-term impacts. 

OPERATION AND MAINTENANCE 

Calibrate application equipment to ensure accurate distribution of material at planned rates. 

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Inspect and evaluate surface applied amendments after the first heavy precipitation event to ensure the

material is stable and does not impact non-target areas. 

Evaluate the effectiveness of the amendment (application, amount of cover provided, durability, etc.) and

adjust future management or type of amendment to better meet the intended purpose(s). 

REFERENCES 

Association of American Plant Food Control Officials. 2019. AAPFCO Product Label Guide.

http://www.aapfco.org/pdf/product_label_guide.pdf

European Biochar Certifications 2022. Guidelines of the European Biochar Certificate version 10.1E 2022.

https://www.european-biochar.org/media/doc/2/version_en_10_1.pdf 

Gelardi, D.L. and S.J. Parikh. 2021. Soils and beyond: Optimizing sustainability opportunities for biochar.

Sustainability 13, 10079. 

International Biochar Initiative. nd. IBI Biochar Standards version 2.1. https://biocharinternational.org/characterizationstandard/

Joseph, S., A.L. Cowie, L. VanZwieten, N. Bolan, A. Budai, W. Buss, M.L. Cayuela, E.R. Graber, J.A.

Ippolito, Y. Kuzyakov, Y. Luo, Y.S. Ok, K.N. Palasooriya, J. Shepherd, S. Stephens, Z. Weng, and J.

Lehmann. 2021. How Biochar Works, and When It Doesn’t: A Review of Mechanisms Controlling Soil and

Plant Responses to Biochar. Global Change Biology-Bioenergy 13:1731-1764.

https://dio.org/10.1111/gcbb.12885

U.S. Composting Council. n.d. “STA Certified Compost Testing Limits.”

https://www.compostingcouncil.org/page/TestResultLimits

US EPA Pollutant Limits https://www.ecfr.gov/current/title-40/chapter-I/subchapter-O/part-503/subpartB/section-503.13. 

USDA NRCS. 2007. Nutrient Management Technical Note 7 (Title 190). Reducing the Risk of E. coli

0157:H7. Washington, D.C. https://directives.sc.egov.usda.gov/

USDA NRCS. 2010. National Engineering Handbook (Title 210), Part 637, Chapter 2, Composting.

Washington, D.C. https://directives.sc.egov.usda.gov/

USDA, NRCS 2011. National Agronomy Manual. 190-V. 4th Ed. https://go.usa.gov/xVdWq 

USDA, NRCS 2022. National Range and Pasture Handbook (Title 190), Part 645, Subpart G, Rangeland

Ecohydrology. Washington, D.C. https://directives.sc.egov.usda.gov/

USDA, NRCS 2022. The PLANTS Database National Plant Data Team, Greensboro, NC USA.

https://plants.usda.gov/home

USDA National Organic Program Regulations (7 CFR Part 205). http://www.ecfr.gov/cgi-bin/textidx?c=ecfr&sid=3f34f4c22f9aa8e6d9864cc2683cea02&tpl=/ecfrbrowse/ Title07/7cfr205_main_02.tpl.

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