October 27, 2009

Q: With this year’s above average corn height and ear placements 6 feet or higher on the plant, do we still want to pick the corn leaving an average stubble height or should stubble height be higher.

Also, we plant our soybeans no-tilled along side our standing corn stalks. This generally works well until damp conditions during harvest cause problems. Today’s hybrids don't break down and rot like they used to. Is there something, besides nitrogen, that you can apply on these corn stalks to help break them down?

A: The corn is very tall and some producers may be tempted to run the corn heads a little higher this year (as long as the corn keeps standing). However, with the systems approach to no-till in mind, I still like to run the corn head about 18 inches off the ground. That leaves the stubble about toolbar height on the planters and drills. Running higher than that may cause problems with hoses, wires, cables, and chains being snagged on the residue next planting season.

Running this height leaves enough stubble to keep the wind off the soil surface, reducing the amount of residue that's blown around, and allows for some snow capture. Also, running this height processes most of the stalk through the snapping rolls so that the residue is broken open and exposed to the soil microbes. Running higher will result in much more residue lasting longer into the next season.

If you run higher, a lean bar on the front of the planter or drill will lean the stalks over to reduce catching on the planting equipment. But again, the stalks won't be broken open to allow faster cycling back into the soil system. If you need more residue, this is an option.

Regarding harvesting soybeans no-tilled into corn residue: I prefer the 3-inch sickle and guards to allow room for the stalks to get cut off. The 1.5-inch, quick cut systems tend to plug up with corn stalks. Also, I like planting directly down the old corn row so that the planter runs over the corn stalks (set the planter deeper to get the seeds into the soil). Then the stalks decompose faster and aren't as much of a problem at harvest. If it's dry, we can harvest either direction, however, if the stalks are damp, we tend to harvest in the direction the stalks are leaning (the direction of planting).

I haven’t worked with any of the products to hasten residue breakdown, and usually am more concerned with how to keep the residue longer. Nitrogen does feed the soil microbes to help balance the carbon to nitrogen ratio of the corn stalks to get faster breakdown. However, that only works if the residue is in contact with the soil and the microbes. Tall, dry stalks after harvest won't break down much as there isn't much biological activity. If you're considering spraying on some nitrogen, do it in the early spring as herbicide carrier for your early preplant and winter annual weed control application. Applying it in fall isn't real effective as many of the microbes become less active as the weather cools and potential nitrogen losses are much higher.

I have discovered that drilling a cover crop into standing corn stalks really speeds the residue breakdown. The drill does cut up the residue some and puts more of it in contact with the soil. The growing cover crop helps feed the microbes and the humidity under the growing cover crop speeds breakdown. Using a brassica cover crop will break down almost all the residue, resulting in too little cover remaining if the cover crop is seeded early enough to get some good growth. A legume cover crop will help balance the C:N ratio and make some N for the next crop. There are several options and we need more work and experience on which ones to select and how to manage them.

Paul Jasa
Extension Engineer