Although having some of the leftover soil nitrogen stay in a (grass) cover crop for a subsequent corn crop may seem to be a good way to recycle nitrogen, allowing rye or wheat cover crops to grow into the spring can interfere with establishing the corn crop, especially if it is to be planted in early April. Managing a grass cover crop to establish soybeans might be easier, although wet soils and a heavy cover-crop residue can present challenges for any crop that follows a cover crop.
Soybeans will be able to take up some of the nitrogen released by the breakdown of a cover crop, but then might fix less from the atmosphere, depending on when the nitrogen is released. Thus, there not likely to be a significant economic gain from having a cover crop tie up nitrogen and release it during soybean growth. However, it will keep some nitrogen in the field, thereby reducing the amount that reaches surface water.
“While we know there is some nitrogen left in dry soils now, the amount available to next year’s crop will depend on the weather between now and next spring,” Nafziger said.
Other factors associated with a drought-damaged corn crop may actually improve field conditions for the next corn crop. Corn that stops growing in mid-season does not produce much lignin, so its residue is softer, it breaks down faster, and planting into it is easier. There is also less residue to contend with.
“This is not a suggestion to plant more corn and fewer soybean acres next year following this year’s corn crop,” said Nafziger. “Corn following corn is showing more stress effects again this year, in some areas for a third year in a row. Even though a field with a short corn crop this year may be more ‘corn-friendly’ than normal next year, it is unlikely that corn following a corn crop – even a low-yielding one – will yield more than corn following soybean.”