Editor's note: Earlier this year, Dakota Farmer ran "Cover crop grazing trial falls short," about a cover crop research project failure, of sorts. Gabe Brown, a Bismarck, N.D., rancher, cover crop pioneer and Soil Health Consulting LLC partner, told me he had some ideas on why that project didn't turn out like expected. The following is his second in a four-part series of why cover crops sometimes fail and what you can do to increase your odds of success.
By Gabe Brown and Allen Williams
Let’s examine the first three of the 10 most common causes of failure of a cover crop and consider what we can do to enhance our chances of success.
1. Not determining your resource concern first. Too often, producers do not take the time to determine what they want the cover crop to achieve. This leads to them purchasing and seeding a cover crop that may not address their resource concern. This, more often than not, leads to a poor experience.
Let me give you an example: my phone rang one March day, and the caller informed me that he had an issue with cover crops and wanted to let me know. He proceeded to explain how he had an irrigated field where he had combined the winter wheat off, baled the straw and then seeded it to a monoculture of purple top turnips. The turnips grew well and he turned his cows on them for the winter. I interrupted him: "lLt me guess, and now your fields have no residue?"
"That’s right," he exclaimed. "And now those fields are blowing! How did you know?" I proceeded to tell him that he seeded the wrong cover crop for his resource concern. By baling the straw, he removed most of the residue. He then planted turnips, which are low in carbon and are nitrogen scavengers. They took up leftover nitrogen from the winter wheat crop and then released that N as they ran their life cycle. That accelerated the breakdown of residue. Add to this the fact that the cattle ate what little aboveground biomass there was, and it was a recipe for failure.
To prevent this, one needs to determine what they are trying to accomplish. For example, am I trying to improve nutrient cycling? Increase organic matter? Leave more soil armor? Feed livestock? And the list goes on. We have to know what our goals are before we put seed in the ground.
2. Not allowing adequate time for cover crops to grow. In northern environments, many try planting cover crops after a small grain harvest which only leaves a few weeks prior to frost. There is simply not enough growing days left in the season to get much growth. In that case, one needs to be seeding fall seeded biennials such as cereal rye and hairy vetch. These species can tolerate colder temperatures and provide early spring growth.
In the "corn belt." many try fitting cover crops into their corn-on-corn or corn-soybean rotation. Yes, you can get a cover crop to grow and it will advance soil health a little, but why not diversify the crop rotation by adding a cash crop such as winter wheat which, once harvested, will allow a much greater window of time for a diverse cover crop to take solar energy and, through photosynthesis, pump that energy into the soil?
3. Planting method and machinery. Are you aerially seeding, broadcast seeding or drilling the seed? The method you should use is highly dependent on moisture. If you have irrigation available or farm in a region where moisture is plentiful, then aerial seeding or broadcast seeding are an option for many species of cover crops. However, not for all species. Some species, such as peas, soybeans and mung beans, perform much better if they are drilled into the soil. Also, if you live in a drier environment, then it is best to drill the cover crop to insure good seed to soil cover contact.
One must also make sure that the drill settings correct for the seed mix you are planting. Are you using the correct inoculants for the legumes you are planting? Are you planting after harvest of the cash crop, or planting into the cash crop? For instance, we have farmers who are experiencing good success with planting a diverse cover crop into standing corn at the V4-V5 stage. They are not experiencing any significant yield drag and the covers are ready to grow with vigor once the corn reaches dry down and the canopy is opened, or the corn is harvested for silage.
Brown and Williams are farmers from Bismarck, N.D., and Winston-Salem, N.C., respectively and partners in Soil Health Consultants, LLC.