The final version of the Iowa Nutrient Reduction Strategy, released this past May by the Iowa Department of Agriculture & Land Stewardship, lists annual cover crops as the most influential practice for reducing nitrogen loss from fields that are in continuous row crop production. The reason cover crops work is largely because they take up nitrate from the soil in the fall and spring. Nitrogen stored in the organic matter created by the cover will be released over time. But depending on what the cover crop variety is and how much growth there was, the amount available for the next crop can vary significantly.
While there are edge-of-field structures such as grass buffers and permanent seeding options that could make more of a difference, a properly seeded, well-established cover crop could reduce nitrate loading in surface waters by about 30%, according to the information collected by the Iowa State University science team advising state ag officials who wrote the Iowa Nutrient Reduction Strategy.
"Trouble is, we haven't been able to consistently get a cover crop seeded and established in the limited number of On-Farm Network cover crop replicated strip trials our growers have put out recently," says Mick Lane, communications director for the On-Farm Network. "Last year's replicated strips, in particular, were hindered by the lingering drought. It's a dry summer in Iowa again in 2013. We're hoping the trials that are being seeded during August this year (the ones that have been planted for the past month on prevented planting acres) will get enough moisture to grow."
1. Timely seeding. Experts say that in Iowa, seeding for a cover crop should be done by planting it in a standing crop of corn or soybeans, just as the leaves are beginning to turn. At that point, sunlight is starting to break through the crop canopy, allowing the cover the necessary light to germinate.~~~PAGE_BREAK_HERE~~~
2. Proper seed variety or mixture. A number of cover crops are available, including rye and other winter cereal grains, spring oats, annual rye grass, vetch, clover, radish, and more. Some, like radish, spring oats, and annual ryegrass will not overwinter. Winter grains and perennials like clover may require that you apply herbicides to control them before you plant row crops such as corn or soybeans into the cover crop the following spring. Should you seed some legume as a cover crop, or perhaps a mixture of a legume with a non-legume or grass? Legumes, if seeded early enough, may also add nitrogen to the soil through their natural interaction with soil Rhizobia.
3. Seeding method. There are specific advantages to both aerial seeding and drilling cover crops, notes Lane. With aerial seeding, the seed can be applied more timely and much faster, but there could be germination problems, especially if moisture is limited.
Seeding with a drill usually will result in better stand establishment but the seeding window is smaller, especially in years like this year, when the crop has been delayed in development. The crop must be harvested before planting. A drill is a very good option if the cover crop seeding follows sweet corn or a silage or high moisture grain harvest.
Cover crop replicated strip trial opportunities with the On-Farm Network
The On-Farm Network is looking for growers all around the state who are interested in conducting replicated strip trials with cover crops this fall. Preferably, these trials will be seeded into standing crops. "We have seed available and can also provide assistance with seeding," says Lane. "As part of our work with the USDA Natural Resources Conservation Service in Iowa, we're also looking for growers located in the Upper Cedar River Watershed in northeast Iowa who would be willing to put out at least one of these trials. We need 10 trials in this area of the state this year."~~~PAGE_BREAK_HERE~~~
He adds, "We're teaming up with ISA Environmental Programs and Services in the Upper Cedar River project. Environmental Programs and Services is looking for growers in other watersheds, as well. If you'd like to participate in this project, or have questions regarding this work, email Tristan Mueller, firstname.lastname@example.org, or call him at 515-334-1075. He'll either have answers for you or get you in touch with someone who can help."
4. Seeding rate. Thin stands, even if established early, may not provide necessary soil protection over winter, and will not work well at sequestering excess nutrients from the soil. For aerial seeding a higher seeding rate is necessary than if the cover crop is drilled.
An Internet search will turn up a lot of additional information on cover crops. Some sites of particular interest are:
* 2013 On-Farm Network Conference
* Cover Crop Solutions–planting tips
* Iowa State University
* Leopold Center for Sustainable Agriculture
* Practical Farmers of Iowa
* Midwest Cover Crops Council
* Purdue University
The On-Farm Network is working now to establish replicated cover crop strips on fields that were not planted this year due to weather and wet soil issues. "We are also still looking for farmers to put out cover crop replicated strip trials after harvest this fall," says Lane.