Soil Conservation Service s1

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NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD MULCHING (Ac.)

CODE 484

DEFINITION The mulch material shall be evenly applied and, if necessary, anchored to the soil. Tackifiers, Applying plant residues or other suitable emulsions, pinning, netting, crimping or other materials produced off site, to the land surface. acceptable methods of anchoring will be used if needed to hold the mulch in place for specified PURPOSE periods. . Conserve soil moisture The application of some mulch materials may . Moderate soil temperature not allow for good air and water penetration creating water logged soils or cool soil . Provide erosion control temperatures. Mulch installation may need to be . Suppress weed growth delayed if these conditions exist. . Facilitate the establishment of vegetative Mulch materials shall be air-dry, reasonably light cover in color, and not be musty, moldy, caked, or of low quality due to foreign materials such as . Improve soil condition weeds. . Reduce airborne particulates As a minimum, manufactured mulches shall be applied according to the manufacturer’s CONDITIONS WHERE PRACTICE APPLIES specifications. This practice applies to all lands where mulches Mulching operations shall comply with federal, are needed. This practice may be used alone or state and/or local laws and regulations during in combination with other practices. the installation, operation and maintenance of this practice. CRITERIA Mulch material shall be relatively free of disease, General Criteria Applicable To All Purposes pesticides, chemicals, noxious weed seeds, and other pests and pathogens. The selection of mulching materials will depend primarily on site conditions and the material’s Additional Criteria To Conserve Soil Moisture availability. Mulch materials shall consist of natural and/or artificial materials that are Mulch materials applied to the soil surface shall environmentally safe such as plant residue, provide at least 60 percent surface cover to wood bark or chips, gravel, plastic, fabric, rice reduce potential evaporation. hulls, or other equivalent materials of sufficient dimension (depth or thickness) and durability to Additional Criteria To Moderate Soil achieve the intended purpose for the required Temperature time period. Mulch materials shall be selected and applied to Prior to mulching, the soil surface shall be obtain 100 percent coverage over the area prepared in order to achieve the desired treated. The material shall be of a significant purpose. thickness to persist for the period required for the temperature modification.

NRCS, OK February 2009 472 - 2

Mulch material shall be applied prior to moisture adequate light and air penetration to the loss. Prior to mulching, ensure soil under seedbed to ensure proper germination and shallow rooted crops is moist, as these crops emergence. Mulching is generally performed require a constant supply of moisture. after grading, soil surface preparation and seeding or plantings are complete. Mulch See Table 1 for mulching characteristics. should be applied in a way that will not shade, or interfere with plant growth. Additional Criteria To Provide Erosion Control Hay mulches of native prairie grass, weeping love grass, yellow bluestems, tall fescue, and Mulch material should be distributed evenly over sorghum shall be used on sites where the area the site and protected from disturbance. Most of will not have a permanent cover of vegetation for the mulches listed in Table 1 will provide at least 6 months. Straw from small grains may adequate erosion protection on slopes less than be used on sites that need protection for 3 3%. They may require anchoring materials to months or less. hold in place on steeper slopes. Hay mulches on stronger sloping sites can be anchored to the Hay mulches shall be distributed evenly over the soil by disking or any other appropriate method. area needing protection at a minimum rate of 2.5 tons/ac (1 lb/sq. yd.). Mulch should be applied When mulching with cereal grain straw or grass after the seeding operation unless needed to hay, apply at a rate to achieve a minimum 70 protect the area prior to seeding. When hay percent ground cover. Mulch rate shall be mulch is used on areas with the potential to be determined using current erosion prediction removed from the site by wind or water, it should technology to reach the soil erosion objective. be anchored with the soil by disking (using When mulching with wood products such as straight coulters) or other appropriate methods. wood chips, bark, or shavings or other wood Protect mulched areas from disturbance. materials, apply a minimum 2-inch thickness. Additional Criteria To Improve Soil Condition When mulching with gravel or other inorganic Apply mulch materials with a carbon to nitrogen material, apply a minimum 2 inch thickness. ratio (C:N) less than 30 to 1 such as animal Materials shall consist of pieces 0.75 to 2 inches manure or legume forage hay, so that soil in diameter. nitrogen is not immobilized by soil biota. Do not See Table 1 for mulching characteristics. apply mulch with C:N less than 20:1 to an area of designed flow in watercourses. Additional Criteria To Suppress Weed Use the Soil Conditioning Index (SCI) to assess Growth soil quality impacts and to determine the type The thickness of mulch will be determined by the and rate of the mulching material. size of the plant being mulched. Small plants Saline or Alkali Soils must not be smothered. Mulches shall be kept clear of the stems of plants where disease is Soils with saline or alkali problems generally likely to occur. Mulches applied around growing have a very poor surface moisture infiltration. plants or prior to weed seedling development Large amounts of organic material incorporated shall have 100 percent ground cover. Thickness into the top 4 to 6 inches of soil creates pore of the mulch shall be adequate to prevent space for water to enter and reduces the wick- emergence of targeted weeds. Plastic mulches like capillary movement to the surface that may be used. occurs during dry periods. Soils with saline or alkali problems require additional management. See Table 1 for mulching characteristics. Follow the guidance in the Oklahoma NRCS Salinity and Sodic Soil Management (610) Additional Criteria To Establish Vegetative standard for total treatment of these soils Cover conditions. Mulch shall be applied at a rate that achieves a Hay from native prairie grass, weeping love minimum of 70 percent ground cover to provide grass, yellow bluestems, tall fescue, sorghum, protection from erosion and runoff and yet allow small grains, or barnyard manure applied at a NRCS, NHCP June, 1994

484 - 5 rate of 15 to 20 tons/ac. in the top 4 to 6 inches Mulching may also provide habitat for beneficial shall be used for organic material. insect and provide pest suppression. Land applications of sewage sludge (biosolids) Clear and infra-red transmissible (IRT) plastics may be used for organic material. Dry weight of have the greatest warming potential. They are the biosolids, pound for pound, will be transparent to incoming radiation and trap the comparable to the grass mulches. Land longer wavelengths radiating from the soil. application rates and locations for biosolids must Black mulches are limited to warming soils by be developed by the Oklahoma Department of conduction only and are less effective. Environmental Quality. A hay mulch of 2.5 Clear mulches allow profuse weed growth and tons/ac will be applied to the soil surface after may negate the benefits of soil warming. Black sewage sludge application and seeding or mulches provide effective weed control. planting of the area. Wavelength selective (IRT) plastic provides the Additional Criteria to Reduce Airborne soil warming characteristics of clear mulch with Particulate Matter from Wind Erosion the weed control ability of black mulch. Mulch rate shall be determined using current Low permeability mulches (e.g. Plastic) may wind erosion prediction technology to reach the increase concentrated flow and erosion on un- soil erosion (movement of particulates offsite) mulched areas. objective. Consider potential toxic alleleopathic effects that See Table 1 for mulching characteristics. mulch material may have on other organisms. Animal and plant pest species may be CONSIDERATIONS incompatible with the site. Evaluate the effects of mulching on evaporation, Consider the potential for increased pathogenic infiltration and runoff. Mulch material may affect activity within the applied mulch material. microbial activity in the soil surface, increase Keep mulches 3 to 6 inches away from plant infiltration, and decrease runoff, erosion and stems and crowns to prevent disease and pest evaporation. The temperature of the surface problems. Additional weed control may be runoff may also be lowered. needed around the plant base area. Mulch material used to conserve soil moisture Weed seed may be found in the mulch material. should be applied prior to moisture loss. Prior to Weed growth should not interfere with the mulching, ensure soil under shallow rooted intended purpose or escape through the mulch crops is moist, as these crops require a constant material. supply of moisture. Deep mulch provides nesting habitat for ground- Mulch materials with a high water holding burrowing rodents that can chew extensively on capacity and/or high impermeability to water tree trunks and/or tree roots. Light mulch droplets may adversely affect the water needs of applied after the first cold weather may prevent plants. rodents from nesting. Fine textured mulches (e.g. rice hulls) which Some mulch material may adversely affect allow less oxygen penetration than coarser aquatic environments through changes in water materials should be no thicker than 1 or 2 chemistry or as waterborne debris. Consider inches. placing mulch in locations that minimizes these Mechanically applied hay mulch shall not be risks. applied when wind velocities exceed 15 miles Consider federal and/or state listed Rare, per hour. When spread by hand, the bales of Threatened, or Endangered species when hay must be torn apart, “fluffed up”, and spread applying this practice. uniformly over the area. Organic materials with C:N ratios of less than 20:1 will release nitrate-nitrogen which could cause water quality impairments.

NRCS, NHCP June, 1994 472 - 4

PLANS AND SPECIFICATIONS Properly collect and dispose of artificial mulch material after intended use. Specifications shall be prepared for each site and purpose and recorded using approved Monitor and control undesirable weeds in specification sheets, job sheets, technical notes, mulched areas. narrative statements in the conservation plan, or other acceptable documentation. REFERENCES Documentation shall include: Agriculture and Agri-Food Canada. 2000. Plastic Mulches for Commercial Vegetable  Purpose of the Mulch Production. Canada-Saskatchewan Irrigation  Type of mulch material used Diversification Centre. Outlook, Saskatchewan.  The percent cover and/or thickness of mulch Natural Resources Conservation Service. 2002. material National Agronomy Manual, Part 506 190-V. USDA-NRCS. Washington, D.C.  Timing of application Renard, K.G., G.R. Foster, G.A. Weesies, D.K.  Site preparation McCool, and D.C. Yoder. 1997. Predicting Soil  Listing of netting, tackifiers, or method of Erosion by Water: A Guide to Conservation anchoring, and Planning With the Revised Universal Soil Loss Equation (RUSLE). U.S. Department of  Operation and maintenance. Agriculture, Agriculture Handbook No. 703. Pp. 175,177-179. OPERATION AND MAINTENANCE Shaffer, M.J., and W.D. Larson. 1987. NTQM, A Mulched areas will be periodically inspected, Soil-Crop Simulation Model for Nitrogen, Tillage, and mulch shall be reinstalled or repaired as and Crop Residue Management. U.S. needed to accomplish the intended purpose. Department of Agriculture, Agricultural Research Service. Conservation Research Report 34-1. Removal or incorporation of mulch materials Pp. 83. shall be consistent with the intended purpose and site conditions. Toy, Terence J., and George R. Foster, Co- editors. 1998. Guidelines for the Use of the Operation of equipment near and on the site Revised Universal Soil Loss Equation (RUSLE) shall not compromise the intended purpose of Version 1.06 on Mined Lands, Construction the mulch. Sites, and Reclaimed Lands. U.S. Department Prevent or repair any fire damage to the mulch of the Interior, Office of Surface Mining and material. Reclamation.

NRCS, NHCP June, 1994 TABLE 1 484 - 5

Mulch Uses Reduce Mulch Thickness Conserves Moderates Erosion Suppress Est. Veg. Improves Soil Comments airborne Material of Soil Moisture Soil Control Weeds Cover Fertility particulates Application Temperature

Peat Moss 1 inch Poor Fair – Poor Poor Fair - Good Fair Poor Poor Expensive, value is in Forms crust, Dries out Forms Decomposes Subject to conditioning the soil. Most repels water, easily, must crust, can slowly, adds wind effective as mulch around draws be kept be washed very little blowing ornamentals. moisture damp and blown nutrients to from soil away the soil Sawdust* 1 – 2 inches Fair Good Poor – Fair Good Poor Poor F Fair air Best used for garden (partially Can crust When kept Can wash Very High paths and around rotted or 3 – 4 inches preventing moist away C:N ratio ornamentals and trees decomposed) (Trees) water plantings. Fresh saw dust penetration can crust. Cotton Hulls* 1 - 2 inches Good Good Fair Good Poor Po Good Fair Wind and Subject to water can wind remove blowing

Compost 1 - 4 inches Good Good Poor - Fair Good Fair G Good Good May be expensive. Can be When Excellent for enriching the washed applied in soil away thick layer Lawn 2 – 3 inches Fair - Good Good Poor – Fair Fair - Good Poor Fair - Good Fair Green grass clippings will Clippings (dry Can Can be Subject to produce heat and odors, clippings) compact and removed by wind may contain viable seed seal water blowing preventing water from penetrating

NRCS, NHCP June, 1994 472 - 6 TABLE 1 (continued)

Mulch Uses Mulch Thickness Reduce Comments Conserves Moderates Erosion Suppress Est. Veg. Improves Material of airborne Soil Soil Control Weeds Cover Soil Fertility Application particulates Moisture Temperature Pine Needles 4 – 8 inches Fair - Good Fair - Good Fair - Good Fair - Good Poor Fair - Good Fair Good for acid-soil plants, (shred before Subject to long lasting incorporating) wind blowing

Straw, Hay* 4 – 8 inches Good Good Good Good Good Fair – Good Good Decomposes and must be (not chopped) (2.5 T/ac) May need to Must be Must be replenished periodically to be mixed anchored anchored control weeds, may with soil to contain many weed seed anchor Leaves* 3 – 8 inches Good Good Fair Fair - Good Poor Fair – Good Fair Contributes many valuable (shredded May need to Subject to nutrients and partially be lightly wind blowing decomposed) mixed with soil to anchor Bark and 2 - 4 inches Good Good Fair Good Poor Poor Good Decomposes slowly, well Wood Chips, water and can be for permanent plantings. Wood air removed by Black Walnut bark and Shavings* movement runoff wood are very toxic to good many plants 2 – 8 inches Fair – Good Fair - Good Fair Good Poor Poor Fair Good to use between Shredded water when kept Wind and Subject to garden rows, better when Newspaper penetration moist water can wind blowing covered with other organic (wet to keep is fair, dries removeTABLE 1 (continued) mulches in place) out quickly

Mulch Uses

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Mulch Thickness Reduce Comments Conserves Moderates Erosion Suppress Est. Veg. Improves Material of airborne Soil Soil Control Weeds Cover Soil Fertility Application particulates Moisture Temperature Manure 1 - 2 inches Good Good Poor - Fair Fair Good Good Fair May contain weed seed, (Partially Can be can burn tender roots on decomposed) removed by vegetable and other water ornamental plants

Landscape 1 layer Good Good Fair to Good Fair - Good Poor Poor Good Can be covered with Fabric (Weed When Weeds may desired mulch, Barriers) anchored to germinate decomposes very slowly the soil on top of fabric Black Plastic 1 layer Good Good Good Good Poor Poor Good Labor intensive, Conserves Warms soil When When expensive, does not moisture anchored to anchored to decompose, adds nothing but will not the soil the soil to the soil allow water to penetrate, may create extreme conditions from water logging soil to drying soil out Pea Gravel 2 inches Fair Good Fair Fair Poor Poor Good Expensive, labor Generally intensive, permanent warms soil mulch

* Mix one pound of actual nitrogen per 50 lbs. of dry material to provide for decomposition.

NRCS, NHCP June, 1994