United States Department of Agriculture 484-CPS-1

NRCS, NHCP

January 2024

Notice of Proposed Changes to the National Handbook of Conservation Practices 

for the Natural Resources Conservation Service

[Docket No. NRCS-2023-0022]

PROPOSED FULL TEXT FOR PRACTICE STANDARD CODE 484

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 

MULCHING 

CODE 484 

(ac)

DEFINITION 

Applying plant residues or other suitable materials to the land surface. 

PURPOSE 

This practice is applied to achieve the following purpose(s): 

• Improve the efficiency of rain-fed moisture management. 

• Improve irrigation energy efficiency. 

• Improve the efficient use of irrigation water. 

• Prevent excessive bank erosion from streams, shorelines, or water conveyance channels. 

• Reduce ephemeral gully erosion. 

• Reduce sheet, rill erosion. 

• Reduce wind erosion. 

• Improve plant productivity and health. 

• Reduce particulate matter emissions. 

• Reduce plant pest pressure. 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies to all lands where mulches are needed. 

CRITERIA 

General Criteria Applicable to All Purposes 

The selection of mulching materials will depend primarily on the purpose(s) for the mulch application, site

conditions, and material availability. The mulch materials may consist of natural or synthetic materials of

sufficient dimension (depth or thickness) and durability to achieve the intended purpose for the required

time period. 

Prepare the soil surface to achieve the desired purpose. 

Apply the mulch material evenly. Use tackifiers, emulsions, pinning, netting, crimping, or other methods of

anchoring, if needed, to hold the mulch in place for specified periods. 

In cases where furrow erosion may occur due to concentrated flows from mulches (e.g., impervious plastic

mulches on beds), take appropriate measures to protect the furrows and the furrow outlets. 

Apply manufactured mulches according to the manufacturer’s specifications. 
Remove non-biodegradable synthetic mulches from the field prior to the next crop. Do not incorporate

(e.g., disk) non-biodegradable synthetic mulches into the soil. 

When mulching with wood products (e.g., wood chips, bark, or shavings), apply a minimum 2-inch

thickness of particles that remain in place during heavy rainfall or strong wind events, or both if applicable. 

The minimum size of mulching material consisting of gravel or other inorganic mulching is 0.75 inches and

applied to a minimum depth of 2 inches. 

When mulching with cereal grain straw or grass hay, apply at a rate to achieve a minimum 70 percent

ground cover. Determine the mulch rate using the current erosion prediction technology for the intended

purpose. 

Do not apply plant-based mulch materials with a carbon (C) to nitrogen (N) ratio of less than 20:1 to

watercourses. 

Additional Criteria to Improve the Efficiency of Rain-fed Moisture Management, to Improve Irrigation Energy Efficiency, or to Improve the Efficient Use of Irrigation Water 

Apply mulch materials to cover at least 90 percent of the soil surface to reduce potential evaporation. 

Fine textured mulches (e.g., rice hulls), which allow less oxygen penetration than coarser materials,

should be no thicker than 2 inches. 

Additional Criteria to Improve Plant Productivity and Health 

When establishing vegetative cover, apply mulch at a rate that achieves a minimum of 70 percent ground

cover to provide protection from erosion and runoff and yet allow adequate light and air penetration to the

seedbed to ensure proper germination and emergence. 

Materials selected and applied to moderate soil temperatures for optimal growth shall provide more than

90 percent coverage over the area treated and shall be of a sufficient thickness to persist for the period

required for the temperature modification. 

Additional Criteria to Reduce Plant Pest Pressure 

Apply mulch at a rate that achieves a minimum of 90 percent ground cover to minimize weed seed

germination and emergence. 

Select mulch materials to disrupt particular pests by color and/or reflective characteristics. 

CONSIDERATIONS 

Evaluate the effects of mulching on evaporation, infiltration, and runoff. Mulch material may affect

microbial activity in the soil surface, increase infiltration, and decrease runoff, erosion, and evaporation.

The temperature of the surface runoff water may also be lowered. 

To reduce environmental impact of synthetic mulches, use biodegradable synthetic mulch if appropriate to

address resource concern(s). Note that some biodegradable mulches will degrade in place (i.e., can be

disked into the soil) while others are better broken down by removal from the field and composted in an

appropriate facility. It is important to know the nature and behavior of the biodegradable material to know

the best disposal procedure. 

Mulch materials with low permeability may adversely affect the water needs of plants. 

When treating areas prone to fire provide fire breaks or use other appropriate methods to mitigate fire

hazards. 

Avoid the use of mulches that are likely to contain invasive pests. Fire scars are particularly vulnerable to

the establishment of invasive plants. 

-CPS-2

NRCS, NHCP

484

January 2024
Avoid excessively thick or tightly packed mulches that can result in soggy anaerobic conditions at the soil

surface during wet weather or prevent rainfall or overhead irrigation from reaching the soil during times of

moisture deficit. 

Use plant-based mulching materials of suitable quantity and quality to add organic matter, provide food

and shelter for soil biota, and protect the soil surface from raindrop impact and crusting, while allowing for

adequate soil aeration. 

Organic materials with C:N ratios of less than 20:1 will release nitrate-nitrogen that can cause water

quality impairments. 

Finely divided plant residues (e.g., sawdust) and those rich in soluble carbohydrates (e.g., fresh greenchopped sorghum-sudangrass, corn, or other grasses) that have a C:N ratio greater than 30 can tie up

soil N and necessitate supplemental N applications on crops. Coarser materials such as grain straw and

chipped brush usually do not reduce crop-available soil N levels unless and until they are incorporated

into the soil by tillage or cultivation. 

Mulching may also provide habitat for beneficial organisms. 

To provide habitat for ground beetles, spiders, and other predators of weed seeds and crop pests, use

mulch of sufficient ground cover and suitable thickness and texture for the target species. Avoid

excessively thick or tightly packed mulches, which can interfere with the movement of ground beetles and

other beneficial organisms, prevent ground nesting of solitary bees and wasps, and may increase the

incidence of crop pests and diseases. Consider mulching crops only if the selected mulching materials,

and rates of application do not contribute to pest problems. 

During the period when weed seed predation is desired and predators are most active, avoid pesticide

applications or pesticide exposures that could adversely affect weed seed consumers. 

Low permeability mulches (e.g., plastic) may increase runoff and erosion on unmulched areas. 

There are potential beneficial or detrimental effects of mulching materials on the biotic community

surrounding the crop, including beneficial soil micro- and macro-organisms, as well as plant pathogens

and plant pests. These effects are specific to site, mulch, and crop, and may include enhanced soil

microbial activity, increased or reduced levels of crop diseases, and toxic (allelopathic) activity against the

crop, weeds, or other beneficial or pest organisms. 

Keep mulch 3 to 6 inches away from plant stems and crowns to prevent disease and pest problems.

Additional weed control may be needed around the plant base area. 

Deep mulch provides nesting habitat for ground-burrowing rodents that can chew extensively on tree

trunks and tree roots. Light mulch applied after the first cold weather may prevent rodents from nesting. 

Some mulch material may adversely affect aquatic environments through changes in water chemistry or

as waterborne debris. Consider placing mulch in locations that minimizes these risks. 

Refer to soil survey data as a preliminary planning tool for assessment of areas. Consult a resource soil

scientist or the Web Soil Survey at: http://websoilsurvey.nrcs.usda.gov/app/ to obtain soil properties and

qualities information. 

For organic or transitioning to organic operations, follow all National Organic Program (NOP) rules. 

PLANS AND SPECIFICATIONS 

Develop plans and specifications for each field or treatment unit according to the Criteria section

requirements above, and operation and maintenance section requirements below. Specifications must

-CPS-3

NRCS, NHCP

484

January 2024
describe the requirements to apply this practice to achieve the intended purpose. Record the following

specification components in an approved Mulching (Code 484) implementation requirements document. 

• Purpose of the mulch. 

• Type of mulch material used. 

• Percent cover or thickness of mulch material, as applicable. 

• Timing of application. 

• Site preparation. 

• Listing of netting, tackifiers, or method of anchoring. 

• Removal and recycling/disposal procedures, as applicable. 

OPERATION AND MAINTENANCE 

Periodically inspect the mulched areas and reinstall mulch or repair as needed to accomplish the intended

purpose. 

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

the management or type of mulch to better meet the intended purpose(s). 

Remove or incorporate mulch materials consistent with the intended purpose and site conditions. 

Do not operate equipment near the mulched site that would compromise the intended purpose of the

mulch. 

Properly collect and dispose of synthetic mulch material after intended use. Note that some biodegradable

mulches can be disked into the soil while others should be removed and composted in an appropriate

facility. 

Monitor and control undesirable weeds in mulched areas. 

REFERENCES 

Agriculture and Agri-Food Canada. 2000. Plastic mulches for commercial vegetable production. CanadaSaskatchewan Irrigation Diversification Centre. Outlook, Saskatchewan. 

Bandopadhyay S, Martin-Closas L, Pelacho AM and DeBruyn JM. 2018. Biodegradable Plastic Mulch

Films: Impacts on Soil Microbial Communities and Ecosystem Functions. Front. Microbiol. 9:819. doi:

10.3389/fmicb.2018.00819. Retrieved Nov 2, 2020 from

https://www.frontiersin.org/article/10.3389/fmicb.2018.00819 

Cowan, J. S.; Inglis, D. A.; and Miles, C. A. 2013. Deterioration of Three Potentially Biodegradable Plastic

Mulches Before and After Soil Incorporation in a Broccoli Field Production System in Northwestern

Washington, HortTechnology hortte, 23(6), 849-858. Retrieved Nov 2, 2020, from

https://journals.ashs.org/horttech/view/journals/horttech/23/6/article-p849.xml

Reberg-Horton, S.C., Grossman, J.M.;, Kornecki, T.S.; Meijer, A.D.; Price, A.J.; Place, G.T.; and Webster,

T.M. 2010. Utilizing cover crop mulches to reduce tillage in organic systems in the southeastern USA.

Renewable Agriculture and Food Systems: 27(1); 41–48. Retrieved Oct 20, 2022,

fromhttps://doi.org/10.1017/S1742170511000469 

Renard, K.G.;, G.R. Foster;, G.A. Weesies;, D.K. McCool and D.C. Yoder, Coordinators. 1997. Predicting

soil erosion by water: A guide to conservation planning with the Revised Universal Soil Loss Equation

(RUSLE). U.S. Department of Agriculture, Agriculture Handbook No. 703. 

Shaffer, M.J. and W.E. Larson (ed.). 1987. NTRM, a soil-crop simulation model for nitrogen, tillage and

crop residue management. USDA Conserv. Res. Rep. 34-1. USDA-ARS. 

-CPS-4

NRCS, NHCP

484

January 2024
Sintim, H.Y. and M. Flury. 2017. Is Biodegradable Plastic Mulch the Solution to Agriculture’s Plastic

Problem? Environmental Science & Technology, 51, 1068−1069. Retrieved Nov 2, 2020 from

https://pubs.acs.org/doi/pdfplus/10.1021/acs.est.6b06042 

Toy, T.J. and G.R. Foster. (Ed.) 1998. Guidelines for the use of the Revised Universal Soil Loss Equation

(RUSLE) Version 1.06 on mined lands, construction sites, and reclaimed lands. USDI, OSMR. 

USDA, ARS. 2016.“The Wind Erosion Prediction System WEPS 1.5 User Manual”, USDA-ARS

Agricultural Systems Research Unit, Fort Collins, Colorado. June. URL:

https://infosys.ars.usda.gov/WindErosion 

USDA, NRCS. 2011. National Agronomy Manual. 190-V, 4th Ed. Washington, D.C. 

-CPS-5

NRCS, NHCP

484

January 2024