Figure 1. Crushing knife rolls on combine head don't cut the stalks but merely crush them so decomposers have many points for attacking the stalks while they remain attached to the root
Reports from the field suggest there might be a lot of corn residue left after grain harvest this year. A 200 bu/A corn crop leaves about 5 tons of dry crop residue. In contrast, soybeans leave less than 2 tons/A of residue so its management is a lot simpler. There are many questions and suggestions as to how to manage that much corn residue, especially if farmers want to plant a cover crop immediately after harvest. Most knowledge on the topic is based on experience so opinions will vary. Nonetheless, here are some suggestions based on my observations:
- Make sure your combine feeds minimal fodder through the combine. All the fodder that goes through the combine needs to be spread so it is much better to leave the plant residue where it stood. Trash reduction kits are available for many combine models to achieve improved results, which also help reduce combine power usage and facilitate increased speed of harvest.
- Leave the stalk crushed but attached to the roots. There are many different types of ways to process corn stalks - some cut the residue in many small pieces, which then create a carpet on the soil surface. In my opinion it is much better if the stalks are crushed but still attached to the root. This way the drill doesn't drag residue and has less material to cut through. In addition, crop residue doesn't move with wind or water over the winter if it is anchored. An example of crushing knife rolls can be seen in Figure 1.
- Evenly distribute residue. The residue needs to be spread evenly over the entire combine header width. Otherwise, windrows with thick residue layers will be alternating with barely covered soil making it impossible to set the drill right. Spreading includes stalks, cobs and chaff. Choppers, batt and chaff spreaders help achieve good residue distribution (Figure 2).
- Leave stalks standing. Although there is some evidence that flail mowers can help correct uneven residue distribution, rotary mowers cause increased windrowing of residue. My main concern is, however, that chopping puts all the residue flat on the soil surface making the job of the planting disk or coulter harder.
- Drill into standing stalks. Don't chop the residue. Although there is some evidence that flail mowers can compensate for poor combine residue distribution this is really tying the horse behind the cart because the combine is supposed to do that job. Rotary mowers actually make residue distribution worse - so they are a big no-no. By leaving the heavy, thick portion of corn stalk attached to soil the stalks are anchored and unlikely to obstruct the drill.
- Drill on an angle to previous corn rows. This avoids some drill units running consistently on top of an old corn row.
- Set the drill right to plant seed into the soil. Once residue is evenly distributed, make sure the seeds are planted through the residue into the soil.
- Use a cover crop. The action of the drill further cuts residue in smaller pieces, but the most important is that the cover crop, once up, creates a micro-climate under the canopy that is more moist and populated with decomposers so the decomposition process is sped up.
- Don't apply nitrogen to corn residue. Because the C:N ratio of corn stalks typically ranges from 40-80 which has to be brought down to 10 (C:N ratio of humus) by microbes, they need to get N from the soil. However, corn residue is above the soil while nitrogen fertilizer quickly washes off into the soil. It doesn't seem to be a wise investment to use nitrogen fertilizer to achieve increased decomposition of residue. Instead, focus on a healthy soil.
- Stimulate soil biology. In a healthy soil crop residue is being processed rapidly. In fact, there are reports that residue disappears too quickly if earthworms are numerous. Established practices to stimulate soil health are: use continuous no-tillage; use a diverse crop rotation; use cover crops during fallow periods; return organic residues such as crop residue, manure, and compost to the soil.
Figure 2. Combine with batt and chaff spreaders