Corn stover: When does removal make sense?

Crop residue removal decisions should be field specific.

Demand for corn stover is growing in the United States. Two industries have identified this secondary product as a valuable feedstock, creating market opportunities for growers. One is the cattle feed industry, which is using corn stover as a low cost winter forage. Another, still in the early stages of commercialization, is the cellulosic ethanol industry. Three Midwest cellulosic ethanol production facilities are slated to come online in 2014, their locations were chosen mostly due to the availability of corn stover in their part of the country.

If these markets expand to create similar demand for corn stover in Michigan, how will growers decide if stover harvest is a good fit for their farm? This decision requires the evaluation of several factors including soil organic matter content, slope of the land, soil type, tillage system and soil fertility levels. Let’s take a look at each of these factors individually.

Soil organic matter content. If organic matter levels are less than 2 percent, crop residue should be kept in place to help maintain and build healthy soil.

Slope of the land. Crop residue is valuable in preventing soil erosion. If the slope of a field causes concern for soil erosion from water flow, then crop residue should be left in place to slow the movement of water over the soil. Highly erodible land classification can help to determine specific areas of concern. Erosion prediction tools like RUSLE2 can be used to fine-tune residue needed to reduce erosion.

Soil type. Sandy soils are often low in soil organic matter and have limited water-holding capacity. Soil organic matter builds structure by providing the glue that binds soil particles together. This increases soil tilth, porosity and water-holding capacity. Only excess stover should be removed from sandy soils. The Lucas SOM Calculator can help you determine how much stover to retain.

Tillage system. The large volume of stover produced by a high-yielding corn crop can sometimes be a detriment to the following crop by slowing warming and drying of soil in the spring. Physical placement of seed through the residue and adequate seed-to-soil contact can be especially challenging in minimum or no-till systems. Stover removal can improve these conditions and reduce the need for additional tillage operations to manage residue.

Soil fertility levels. Corn stover contains significant quantities of plant nutrients, especially phosphorus (P) (8.2 pounds per ton) and potassium (K) (32 pounds per ton). If a corn field has low soil test levels of P or K, addition of nutrients in the form of fertilizer or manure will be needed to replace those removed by stover harvest. Conversely, soils with very high fertility levels may benefit from removal of excess nutrients, which could also allow for additional manure applications in the future.

Crop productivity is a critical consideration when deciding whether or not to harvest corn stover. Some growers will be able to remove stover and maintain productivity while others should leave stover in place to ensure successful future crops. Site-specific data should allow corn growers to make this decision within fields with variability and prevent degradation of soil health in sensitive areas.

Michigan State University Extension is conducting on-farm research throughout Michigan on practical issues of corn stover harvest and use. Results from this project will be shared widely as they are compiled.

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