Cover Crops and Nitrogen - Can I Capture Some Nitrogen for Next Spring?

Nitrogen prices are an issue on most producers' minds these days. It appears as if the higher prices are going to be with us for a while and you may be thinking of alternative methods of supplementing nitrogen for corn. One possibility is growing a cover crop after your wheat this summer and allowing it to grow into next spring. One of the questions many Ontario growers have is what kind of nitrogen value might you expect?

The following describes work done by the Ohio State University that addresses this issue, noting that these results are dealing with cover crops established after wheat harvest only.

Ohio State University has established field trials the last couple of years to help answer this question. Experimental plots have been at OARDC's Northwest, Western, and Wooster locations. At the Northwest Research Station in 2007 we did not observe any nitrogen contribution from red clover interseeded into wheat for a subsequent corn crop. We did, however, observe a rotational benefit of 18 bu/acre when red clover was established compared to no cover crop. At the Western Research Station in 2007, we did not observe a rotational benefit associated with the establishment of red clover after wheat harvest nor did we observe a nitrogen contribution. From a separate study at the Western Research Station in 2007, we did see what appeared to be a rotational benefit from field pea established in late September, but we did not see similar results for soybeans, early planted field peas (late August), or annual ryegrass. We did not observe a nitrogen contribution from any of the cover crops. At a fourth trial conducted at the Wooster research location, we did not observe a nitrogen contribution or rotational benefit with annual ryegrass seeded after wheat harvest.

Take home message - based upon last year's findings we cannot definitively identify a nitrogen contribution from the establishment of any cover crop after wheat prior to corn. We did see some rotational benefits (2 out of 4 locations) with legumes, but at the two sites were non-legumes were evaluated we observed no corn yield benefit. There are some research publications from other areas of the U.S. that show nitrogen contributions from legume cover crops, but our research does not corroborate those findings. Establishment of cover crops solely for the purpose of supplementing nitrogen should be approached with caution. Legume cover crops have a greater probability of supplementing some nitrogen (not based on our research, but others have reported this) than non-legumes, but it is not a sure thing. Additionally, establishment of the cover crop is not a guarantee either. The earlier the crop is established the greater the chance of good growth prior to the onset of winter.

Note that these results are only for cover crops established after wheat harvest, when there is little opportunity for red clover growth and nitrogen fixation. Moisture stress, in particular, would limit the amount of N that could be fixed by such a cover crop. Ontario results with clover seeded into the wheat in the spring has indicated a consistent nitrogen benefit to the following corn crop of 60 lb N/ac in no till systems and 73 lb N/ac in tilled systems. N contributions from non-legume cover crops have been negligible, although there may be benefits from improved soil structure and organic matter. N contributions from annual legume crops like field peas have been inconsistent. Further work is required to maximize the benefits from cover crops.