AGRY-95-09

Questions Relative to Harvesting & Storing Corn Stover

Prepared September 1995. Originally published as Agronomy Extension publication AGRY-95-09. Contact the author for hardcopy versions of this document.

Introduction

This document addresses some questions regarding the harvesting and storage of corn stover for the purpose of delivery to a proposed corn-based pulp mill in northwest Indiana. Some of the responses to these questions are based on Purdue Extension writings from the 1970's when harvested corn stover was being evaluated as an alternative energy source for beef cattle. Additional thoughts on these issues are based on recent discussions between Bob Nielsen (Purdue Agronomy Dep.), Sam Parsons (Purdue Ag. & Biological Engineering Dep.), and Dave Petritz (Purdue CES AgNR). We don't pretend to presume to have addressed all the considerations that apply to this venture. We have also restricted our comments to the harvesting and storage of the stover, since we have no knowledge of the pulp-making process itself.

What is the farmer obligated for?

• A farmer must purchase a minimum of four units of equity interest ($10,000) in a paper-pulp mill to be constructed by Heartland Fibers Inc., plus a $250 membership fee.
• Purchase of equity interest in the paper-pulp mill obligates the farmer to produce a minimum of 252 tons of corn stover at a yet-to-be-determined stover moisture content.
• The farmer agrees to allow access to the enrolled acres after grain harvest for the purpose of stover shredding, windrowing, baling, and transport of corn stover by custom operators under contract to Heartland Fibers, Inc.
• The farmer also agrees to store some or all of the large bales on-site until the production plant calls for delivery.

What are the risks involved with corn stover harvest?

• We estimate that the average harvest window to shred, windrow, and bale corn stover will be 40 days after corn grain harvest, after which weather and soil conditions are often not conducive to field traffic and stover harvest.
• Wet weather and muddy fields during and after grain harvest would delay or prevent stover harvest. This is especially critical given the likely dependency on the schedules of custom operators who will be responsible for shredding/windrowing/baling the corn stover.
• Soil compaction and ruts can easily result from extra wheel traffic on excessively wet soils.
• Stover moisture content greater than 30 percent would likely decrease the efficiency of the baling operation, and also decrease the storability of the bales due to increased risk of molding and rotting.
• Corn stover material will generally cause greater wear and tear on harvesting equipment than does alfalfa and grass hay.
• There may be opportunity costs relative to competing fall farm operations.

How much stover is produced in a typical corn field?

• Corn grain accounts for about 45% of the total dry matter yield of a corn field. Corn stover amounts would range from 3 to 4.5 DRY tons per acre in fields ranging from 100 to 150 bushels of grain per acre. DRY ton means exactly that; 2000 lbs. of totally dry stover. You can convert wet weight to DRY weight by multiplying the wet weight by the percent dry matter.
• If 60 percent of the stover would be harvested, then harvested stover amounts would range from 1.8 to 2.7 DRY tons per acre depending on grain yield level. At a stover moisture content of 30 percent, the range of harvested stover would translate to 2.6 to 3.9 tons per acre.

What are the effects of stover removal on soil tilth?

• Hard to estimate, but surface organic matter levels would decrease and equilibrate to a lower level if corn stover were harvested frequently over a period of time. Therefore, we would recommend rotating fields to be harvested for stover from year to year.

What are the effects of stover removal on ground cover and HEL requirements?

• Heartland Fibers Inc. estimates that 40 percent of the corn stover will be left in the field after stover harvest.
• Less ground cover would increase the risks of soil erosion from heavy rains.
• Removal of 60 percent of the stover material would NOT leave sufficient ground cover to satisfy conservation compliance program regulations the following spring, especially if much of the remaining residue was composed of standing stalks.

What is the approximate value of stover nutrients removed from field?

• The approximate amounts of nitrogen, phosphate, and potash removed per DRY ton of harvested corn stover are 13.6, 3.6, and 19.7 lbs. (Adapted from Voss, R. 1993. Nutrients in corn and soybean residue. Integrated Crop Management Newsletter, IC-466(26), Nov 1, 1993. Iowa State Univ., Ames, IA.)
• The approximate value of the nitrogen, phosphate, and potash per DRY ton of harvested corn stover is $2.72, $0.79, and $2.36 (based on $0.20, $0.22, and $0.12 per lb. of nitrogen, phosphate, and potash fertilizers), for total nutrient value of $5.87 per DRY ton.
• If harvested stover amounts ranged from 1.8 to 2.7 DRY tons, then the total value of the nutrients removed from the field would range from about $11 to $16 per acre.

What type and size of package (bales, stacks) is desired?

• The most feasible package would likely be 1-ton bales measuring 4x4x8 ft, produced by the Hesston Big Baler. Such bales are relatively high density, solid, and suitable for transport on a flatbed semi-trailer.
• Other possibilities include large round balers (1/2 ton bales) or stackers (1/2 to 1 ton stacks).

Is any pre-harvest operation, such as windrowing, necessary?

• Yes, quite likely the stover will need to be cut with a rotary hay cutter and raked with a double rake prior to harvesting the stover. A combination flail chopper/windrower could also be used.
• Keep in mind that the tire traffic of the grain harvest operation (combine, grain carts, trucks, etc) will make some percentage of the stover very difficult to harvest.

What type of custom harvesting and transport equipment will be required?

• A combination flail chopper/windrower to prepare the stover for baling.
• A baler to bale the windrowed stover into large bales. As a frame of reference, the Hesston Big Baler sells for at least $50,000. Heartland Fibers Inc. states that only wire tie bales will be acceptable.
• Flatbed trailers or semi-trailers to haul bales to plant.

What is the optimum stover moisture content for harvest?

• Stover moisture content should probably not exceed 30 percent for optimum harvesting.
• As a rule of thumb, percent moisture content of stover is twice that of the grain. For example, the moisture content of stover when you harvest grain at 20 % moisture would be about 40 % moisture.

Where and how will stover be stored?

• The farmer is responsible for storing the stover packages until the processing plant calls for delivery.
• Heartland Fibers Inc. states that 'fiber degradation caused by excessive moisture levels in the baled stover' will result in adjustments in their purchase price to the farmer.
• Heartland Fibers Inc. states that storage site requirements and approved field site locations will be defined in their criteria.
• It is our opinion that to best maintain quality of the stover packages, they should be wrapped and stored on crushed rock or under cover. Depending on the length of time these packages will need to be stored, stover moisture content may need to be 20 % or less.
• Because of the uncertainty of when the plant will call for delivery, the stover packages should be stored on sites that will not interfere with normally scheduled fall or spring field operations.

What is the cost of harvesting and transporting corn stover packages?

• Cost per dry ton of stover to custom harvest will average $8 to $10 per package. Cost of cutting and windrowing the stover prior to harvest will average $4 to $6 per acre. Cost of transporting packages (several miles only) will average $2 to $6 per package. (Source: Purdue Custom Rates, 1994)
• Apparently, the pulp-mill operation will contract directly with custom harvesters and transporters.

Return to The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.

• Return to Chapter 2. Corn Management Information .

The Chat 'n Chew Cafe.

Purdue University Agronomy Extension WWW Home Page.

Purdue Agronomy On-Line! , Purdue's Agronomy Department WWW Home Page.

End of Document