Corn stover: What is its worth?

Corn stover is made up of the stalk, leaves, husks and tassels left in the field after harvesting the grain with a combine. This stover can be used to make advanced biofuels or be used as a low quality, emergency livestock feed. There are a number of factors you should consider before you set a price for corn stover. These include nutrient removal, soil erosion and maintaining soil quality. This article discusses these three issues and how they should influence your decision whether or not to sell corn stover from your farm.

When you remove stover, you are taking nutrients with you. Table 1 shows the nutrient content of corn stover per dry matter ton of stover. The value of these nutrients needs to be calculated into the value of the stover. Since fertilizer prices vary widely through the year and from year-to-year, you might consider developing a simple pricing index. Current prices are listed in Table 1. Over the past five years, they have ranged from $499 to $853 per ton. The price you pay for these nutrients will depend on the time of year you purchase them and the volume of fertilizer you buy. Make sure to use the price you pay – not a national average. Use previous farm records to determine your average cost of nutrients over the past five years and use your own judgment about whether you think prices this year will be higher or lower.

Table 1. Corn stover nutrient removal

* Source: USDA-Illinois Dept. of Ag Market News

Based on these numbers, the value of nutrients removed in the stover is $31.52 per ton. This would be the minimum price you would need to receive in order to break even on the stover. Harvesting, transportation and storage costs are not part of this price.

Soil erosion from wind and water is another important consideration. If too much stover is removed, topsoil can be eroded away from the forces of wind and water. Tillage plays a key role, also. The Revised Universal Soil Loss Equation (RUSLE2) is a tool you can use to determine soil erosion risk from water. It takes into account soil types, rainfall patterns and topography. Every field is different, so the amount of stover you should leave in the field will vary from field-to-field. Your local NRCS staff can help you run the equation or you can download the software.

Preliminary research data from Michigan State University shows that current equipment used to harvest stover can only pick up about 25 percent, leaving 75 percent in the field. Line-transect evaluations show that this level of stover removal more than satisfies the RUSLE2 needs. However, in fields with long, steep hills you might need to leave all of the stover on that part of the field.

Maintaining soil quality is another key concern. Returning stover to the field increases short- and long-term soil carbon pools that help to build soil tilth, infiltration, water retention and nutrient availability. Farmers have long believed that they must return 100 percent of crop residues to maintain soil quality. Today, with improved corn varieties leading to increased yields, this may not be completely true. There are some soil types that produce so much residue it becomes a management problem. High levels of stover on the surface cause soils to warm more slowly in the spring and row cleaners on planting equipment cannot always create a good seedbed for proper planting depth and good soil to seed contact. This varies from soil-to-soil, season-to-season and with varying tillage practices. As a general rule of thumb, most soils in Michigan need about one-third of the corn stover returned to the soil each year to maintain soil organic matter. This leaves about two-thirds of the crop that could be harvested for livestock feed or biofuels.

The bottom line is that you need to consider the soil types on your farm, how much stover should be left to improve the soil and protect it from erosion. These factors will impact long-term sustainable production on your farm.

Once you have done your homework and know how much stover you can remove, the next step is to determine a value for the stover. Make sure you include the nutrient removal cost plus add in some return on your investment. If you figured a 15 percent return on the $31.52 nutrient investment, you would need to price your stover at $36.25 ($31.52 + 15 percent = $36.25) per dry ton. This is the price for the stover in the field – a price that a custom harvester would expect to have to pay for it. Some farmers might place a value on the soil organic matter contribution; however, there is no market for carbon or a good, scientific way to place a value on it, so the number would be arbitrary.

For questions or comments, please contact Michigan State University Extension bioenergy educator Dennis Pennington at 269-838-8265.

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