Residue Management for Erosion Control

DS-22-97, June 1997
Vernon Hofman, Retired Agricultural Engineer

Keeping a protective cover of crop residue on the soil surface is the simplest and surest way to control both water and wind erosion. Residues improve infiltration of water into the soil, reduce evaporation, and help maintain organic matter. Incorporating previous crop residues leaves the soil surface exposed to agricultural runoff, which causes soil erosion.

Erosion Control

Residue management provides a means for limiting both soil particle detachment and removal of soil particles from the field. Vegetative residues reduce raindrop impact and reduce the wind velocity at the soil surface. Residues also create an intricate and complex series of diversion dams that slow water runoff rates and reduce the amount of soil particle detachment. In addition, slowing the runoff rate reduces the capacity of water to transport dislodged soil particles from the field, reducing the erosion rate even more. Moisture is conserved as more time is available for water to infiltrate the soil and evaporation is reduced by the cover on the soil surface. The amount of crop residue produced and subsequently available for erosion control depends mainly on the type and yield of the crop grown and the tillage system used. Generally, higher yields mean more residues. The amount of residue present from seedbed preparation through crop establishment is critical because the greatest potential for erosion occurs from early April to mid-May. The selection and use of a tillage system largely determines the amount of residue cover during this critical period. It is possible to achieve many of the objectives of fall tillage and still provide some protection to the land. There are no firm guidelines for the amount of cover needed to protect land from erosion, but estimates suggest a minimum of 30 percent surface cover on level land. This guideline will vary based on soil type, length of slope, steepness, and the presence of conservation practices such as contouring and crop rotation.

Field Estimate of Residue

The amount of residue produced by a crop is influenced by the growing season, variety, fertilizer program and other factors. As an example, spring wheat crops will produce about 100 pounds of crop residue per bushel of yield. A spring wheat crop yielding 30 bushels per acre, then, will produce about 3,000 pounds of residue per acre (Figure 1).

Example: A 30 bushel per acre crop of spring wheat produces 3,000 pounds of residue per acre.

Figure 2 can be used to convert pounds of residue into percent cover for three crops grown in North Dakota. In the previous example, the pounds of wheat residue would provide about 85 percent ground cover. This is more than enough to provide erosion protection. The minimum requirement of 30 percent cover would be met by about 600 pounds of residue per acre.

Example: A small grain field that has 600 pounds per acre residue has a 30% ground cover.

Other crops would require greater amounts of residue. It takes about 1,000 Ibs. of corn residue or 3,000 Ibs. of sunflower residue to provide a minimum of 30 percent ground cover. Tillage implements vary considerably in how much residue they bury. The approximate percentage of the residue cover remaining on the soil surface after a single pass of different tillage and planting implements is listed in Figure 3. These figures may vary with travel speed, tillage depth and residue condition.

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To obtain the percentage of residue remaining for a specific tillage system, multiply the percentages together for each tillage operation within the selected system. As an example, a tillage system using chisel plow with twisted spikes in the fall and a field cultivator in the spring for seedbed preparation will leave about 22 percent of the previous crop residue on the soil surface at planting time. The chisel plow will reduce the residue 50 percent and overwintering will reduce that amount to about 35 to 40 percent of soil cover. A spring cultivation will reduce that amount to about 21 to 24 percent, not enough for erosion control. As a comparison, the moldboard plow system incorporates almost all residues while the no-till system leaves most of the residue on the soil surface. The effectiveness of erosion control through residue management is shown in Figure 4. While this information is for specific soil and slope, it shows that tillage systems that maintain some residue cover will reduce soil losses. No-till systems, which maintain the greatest amount of surface residue, can result in a 90 percent reduction in soil erosion when compared to the moldboard plow system.

Figure 4. Soil loss associated with various tillage systems used in a wheat-fallow rotation at the High Plains Agricultural Laboratory, Sidney, Nebraska. Water was applied at a rate of 2.5 inches/hours. Tillage operations for moldboard plow systems were plow, spring tooth harrow twice, rodweed twice; and for undercut or subtill, undercut three times and rodweed twice.

Residue Conserves Moisture

An added benefit of residue cover on soil surfaces is moisture conservation. Water that is not allowed to leave the field can soak in and become available for crop use. Eliminating unnecessary fall tillage and leaving some standing residue can also conserve moisture since standing residue traps winter snowfall. An additional inch of stored soil moisture can result in a wheat yield increase of 3 to 5 bushels per acre. Crop residue also acts as a mulch, reducing moisture losses through evaporation. However, reducing evaporative losses can be a disadvantage on wet soils and may delay spring field operations.

Some Residue Problems

Although residue management can effectively control erosion, some problems do emerge with increased residue levels. Residue can provide good weed seed environment and may block herbicide movement to the soil. Moist soils may interfere with herbicide incorporation and low temperatures beneath residue may delay planting and seed germination. Excessive residue can clog implements or otherwise hamper tillage and planting operations. It may also provide a winter habitat for rodents, insects and pathogens. Potential problems should not be ignored. However, good management techniques can minimize many of the disadvantages associated with residue management. Crop and tillage system rotations can help reduce the problems associated with weeds, insects and diseases. Depending on the residue level, chopping or shredding can minimize potential clogging problems.