Cover crop: What the doctor ordered after a drought

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When was the last time you farmed after a devastating drought, and tried to figure out how to balance all of the agronomic challenges it presented. Lack of soil moisture? Herbicide carryover? Fertility needs? Biomass? Soil tilth? Dad and Granddad may or may not have worried about any of those, but today’s agriculture will put some or most of those on a high priority list. Although it may take most of the winter to learn how to address most of those issues, it may soon be time to take action on some of those. And to kill multiple birds with one stone, a cover crop may be that stone

You may be new to the concept of a cover crop, and some research may be necessary, but it could be just the answer for questions that you have not yet thought about. Purdue agronomist Eileen Kladivko will tell you that a cover crop will be one way to keep your unused 2012 nitrogen on your farm and recycle it into the 2013 crop.

Her factsheet in a recent Purdue crops bulletin says the residual nitrates that were not used by the crop this year will soon be leached out of the soil by fall precipitation. While she is most concerned about where the nitrates will go (into waterways, streams, and the river), Kladivko says, “For farmers who lose the residual N, they are also losing the opportunity to trap that N and keep it in their fields for subsequent crop use. Cover crops are an excellent practice to scavenge residual N and recycle it through their plant biomass (shoots and roots).”

click image to zoomCover crops Kladivko says when the cover crop decomposes next spring some of the nitrogen it has absorbed will be released for use by the next row crop planted in that field. And some will help build the organic matter in the soil. How much uptake of nitrogen there will be depends on how much residual nitrogen you have in the soil, the type of cover crop that is planted, how much it grows until it is terminated, and how it decomposes next spring. 


But Kladivko says, “This is precisely the type of year when a cover crop is needed, to trap the much larger amount of residual N that will be present after the poor (corn) crop. Cover crops will help the farmer recoup part of the fertilizer N investment from this season, and will provide some benefits in improving soil organic matter and soil biological activity.”


Her study of cover crops points to many other benefits, including protecting against soil erosion, and providing food for soil organisms.

If a cover crop is something that may be of interest, there are many decisions to make, particularly what you are going to plant, and how to manage it.  Kladivko suggests:

  • If the main focus of the cover crop is to scavenge N and build soil organic matter, then grasses such as oats, cereal rye, or annual ryegrass, perhaps mixed with oilseed radish, are good options.
  • If fall grazing is desired, then turnips or crimson clover could be mixed with the oats and cereal rye.
  • Farmers need to consider their next cash crop and have a plan for cover crop termination in the spring, as an important step before seeding cover crops this fall.
  • Careful spring management is essential if cover crops are to be beneficial to the farmer and not pose major difficulties in planting the next crop.
  • The amount of N scavenged by these cover crops is difficult to predict but may be in the 50 to 100 lb N/acre range in a year like this one.
  • Although the amount of N released by the cover crop for next year’s crop is also difficult to predict, it may potentially be up to half of the N in the above-ground biomass, if the cover crops or cover crop mixture have a low C:N ratio and are terminated while in the vegetative state.
  • A pre-sidedress nitrate test (PSNT) would be one way to help determine whether sidedress N applications could be reduced next year.
  • Herbicides applied to row crops this year may have an impact on the cover crop to be planted, so read the label for the herbicide that was used.

Kladivko says a lot of advice is available from the Midwest Cover Crops Council.

Many farmers, who have explored the use of cover crops in the past and have been frustrated with the rules about insuring row crops following a cover crop, are advised that USDA’s recent drought initiatives have addressed some of the issues. While the official authorization has not yet occurred, USDA indicates it will allow insurable row crops to be grown after a cover crop has been cultivated over the winter.

Summary:

Corn ground which may have unused nitrogen could be a great candidate for a fall/winter cover crop, to help with soil retention, capture the unused nitrogen, provide that nitrogen for the next crop, increase soil organic matter, and feed soil organisms. The drought this year has left this year to be a perfect time to plant a cover crop.

Source: FarmGate blog


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