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Nitrogen Contribution of Frosted Corn
If immature corn is cut and incorporated within the next few weeks, I would anticipate a contribution of N to next year′s crop from a plowed-under nature- induced corn green manure crop of about 30 lb N per acre. This number comes from a study in Minnesota by Dr. John Lamb, where sugarbeet followed sweet corn (an early harvested crop, harvested while the stalks and leaves are green) compared with normal field corn harvest. Certainly there is a lot of N in the plants, but there is also a large amount of carbon compounds in the plants. Therefore additional breakdown of corn residue will be relatively slow and a higher amount of the N will be cycled into the soil as organic matter than will be released for general crop consumption next season.
In addition to the 30 lb N credit, it is likely that more N may become available late next season as decomposition continues. This will likely not be a factor in determining yield potential, but might have a role in either increasing or decreasing crop quality depending on the crop seeded in 2005. Slow release N can be beneficial to wheat, because N release late next season can result in higher protein without risk of problems like lodging. However, barley seeded after any of these plowed under crops could be a problem. Late season release, or a particularly good residue N mineralization year could result in higher protein than the malting industry might accept. For that reason, choosing barley after an aborted corn crop would be a poor decision. Another crop to be avoided following plowed-under corn, soybean or dry bean would be sugarbeet. Again, late season N release would not be a benefit, but a liability with a possible reduction in sugar content and beet quality. Putting beets on small grain ground that was harvested for grain, or another harvested for grain crop would be a better plan.
A final recommendation would be delaying fall soil sampling after aborted crops until late in the fall. This is usually not a recommendation I would support following an early grain harvest. However, green manures are different than harvested grain residues, so a delay in soil testing for residual nitrate would be wise.
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