"I've heard from five different sources this past week about cover crops in Iowa and Minnesota being terminated to 'manage' them for next year's cash crops," says Sarah Carlson, Midwest cover crop research coordinator with Practical Farmers of Iowa. "These are poor recommendations and a great loss of opportunity for soil improvements. The best recommendation is don't work the ground this fall. Terminating cover crops this fall is bad advice for a number of reasons."
The 2013 planting season was a struggle not only to get crops in the ground but also to understand the rapidly developing crop insurance and cover crop policies, says Carlson. Farmers and ranchers had numerous questions regarding the use of cover crops on acres qualifying for prevented planting provisions under crop insurance policies. Many farmers did go ahead and plant a cover crop on those acres that were unfit for cash crop planting. Carlson has checked this termination topic with a number of cover crop experts in the Midwest. She offers the following information and recommendations.
Throughout the Upper Mississippi and Great Lakes region cover crops that have been planted this year included: soybeans, crimson clover, hairy vetch, cowpea, Austrian winter pea, cover crop radish, turnips, sorghum-sudangrass, teff, annual ryegrass, winter wheat, winter rye, spring wheat, oats and others.
Why have cover crops on "prevent plant acres?
A big reason farmers have been covering up their soil this summer on prevented planting acres was to not only take advantage of an opportunity to build soil, replenish nutrients and super charge microbes but also to avoid future yield decreases from fallow syndrome, says Carlson. "We rarely hear about fallow syndrome. However the potential for a yield decrease the following year due to fallow syndrome can be worth the cost of planting a cover crop."~~~PAGE_BREAK_HERE~~~
She cites a 1998 publication from Dupont Pioneer by Wiersma and Carter which showed a 12 bushel-per-acre decrease in corn yield where a fallow period had preceded corn planting. They confirmed that fungi populations responsible for converting phosphorus into a plant form had significantly decreased in colonization numbers. Vesicular arbuscular mycorrhizae, or VAM, are important soil microbes and without a living plant feeding their populations, their numbers can dramatically decrease. From four locations across Iowa and Missouri, the Dupont Pioneer publication showed that decreases in the colonies were correlated to a resulting decrease in the following years corn yield (Table 1).
Now that farmers have covered up their soil with a cover crop this summer, many of these farmers are asking -- now what?
"For cover crops planted early in the summer season, farmers are encouraged not to till or incorporate plants that have seed heads," says Carlson. "Leave soil undisturbed and covered all winter long to provide protection from harsh weather."
* An oat cover crop that is producing seed can be allowed to reseed itself without causing a management issue.
* Any winter small grain cover crop such as rye, wheat or triticale need to vernalize to produce a seed head. Cover crops that were planted mid-summer will likely die from old age this fall with a high incidence of winter-kill.
* Farmers are encouraged not to work the ground and instead leave the cover crop residue covering the fields all winter.
* Annual ryegrass cover crops planted mid-summer will likely overwinter in the majority of this region. For best results, plan to manage it in the spring.~~~PAGE_BREAK_HERE~~~
* Farmers who used soybeans as a cover crop may find it advantageous to drill or plant 1.5 to 2 bushels per acre of oats into the stand prior to mid-September. The oats will help capture nitrogen that may leach this fall or next spring ahead of the following cash crop. Without this additional cover, nitrogen losses can be significant. For a normal soybean crop 45 pounds of nitrogen per acre can be leached following that crop. Oats ensure not only protected soil but also capture nitrogen.
* Farmers using a brassica cover crop like cover crop radish, turnips or mustards NOT mixed with a grass species, like oats, are encouraged to also drill, plant or broadcast a grass with a brassica. Brassicas are excellent at scavenging nutrients. However, brassicas decompose quickly the next spring, releasing scavenged fertilizer ahead of the cash crop. To slow down this process a grass species planted with brassicas can better synchronize nutrient release with the demands of the subsequent cash crop.
Didn't plant a cover crop yet? What if you haven't planted a cover crop yet? Now is the time. To maintain any soil moisture that is present in the field, do not work the ground. Drill or broadcast the cover crop seed and then lightly incorporate it today.
What are the next steps to consider regarding cover crops? If you have questions about which cover crop options fit your farm's situation, either on prevented planting acres or for regular cover crop use, contact Sarah Carlson at Practical Farmers of Iowa at 515-232-5661 or [email protected]. She'll connect you with experienced cover crop farmers and can put you in contact with cover crop experts in your state.