Cover Crops - Not Just for Cover Anymore
Depending on the type of cover crop used, other benefits could be addition of organic matter, addition of nitrogen to the soil, scavenging excess nitrogen, maintenance or improvement of soil structure, remediate soil compaction, reduce surface evaporation and enhance soil life.
As many successful no-till farmers have shown from experience, cover crops are not necessarily required for no-till systems to work but there are also many successful no-till farmers that utilize cover crops and believe they improve the productivity of their fields.
No matter what your situation is, you should:
- decide what you want to accomplish with the use of the cover crop
- determine where in your cropping system a cover crop can fit in
- consider agronomic management; seed cost, herbicide carryover, potential pest complications, burn down herbicide selection and timing, seeding equipment and soil preparation, residue management.
Rye, wheat, barley, spring oats, are the most widely used cover crops. All can all serve as a scavenger of left over nitrogen not utilized by the main crop or from fall manure application. This nitrogen will become available to the next years crops only after being released as they break down in the soil. They establish well in the fall although they vary, in the order listed above, in how late the date of seeding can be and still get significant growth for cover over the winter and into spring. Oats will winter kill ninety five percent of the time and residue degrades quickly. The main concern with rye is the possibility of spring growth getting away on you when wetness prevents getting on the field to burn it down. Seed sources, if lined up early enough, are generally available.
Annual ryegrass functions similarly to cereal rye and has been getting a lot of attention lately mainly because of claims that it’s root system grows deep and breaks up soil compaction. Whether it is better than cereal grains for that purpose is debatable. Concern exists about annual ryegrass becoming a problem as a weed, particularly when the crop rotation includes wheat.
If breaking up compaction is your goal, research shows that sorghum-sudan hybrids work well. Being a warm season crop, it too has a limited window of opportunity, possibly after the harvest of a small grain. Farmers that need forage can make use of it as such. But if not, mowing it once is still beneficial as that strengthens its root system and triggers more growth to contribute to the soil, according to research done on this.
Winter Annual Legumes
These nitrogen producing cover crops need to be seeded earlier than the winter annual grasses mentioned; mid-August to very early September. So they find a place in fields following a small grain crop or possibly in early harvested silage fields without herbicide residues that could affect them. Legumes have a low carbon: nitrogen ratio and do not increase long term organic matter as much. That is not to say that they don’t enhance soil tilth. Hairy vetch is a legume that is most often mentioned because of its ability to produce large amounts of nitrogen. However the amount of nitrogen is proportional to how long it grows in the spring, with maximum production at bloom, which can be in late May. There are some named varieties that mature earlier than the common type. Growth in the fall is minimal so some growers mix in some rye or wheat for added cover. Seed is relatively expensive. Crimson clover is another potential legume for August or very early September seeding. It is considered marginal for winter hardiness above the Mason-Dixon Line but it has worked for some growers in southern Pennsylvania. It matures earlier than hairy vetch and seed cost is reasonable (And it really looks nice in the spring if you let it go into bloom).
Other cover crop options and more details on all cannot be covered in the limited space of this article. To find out more, I recommend that you utilize the Sustainable Agriculture Research and Education (SARE) resource Growing Cover Crops Profitably. It is available free on-line to download or the book can be ordered at the SARE website.
If you have internet access, you can view some educational videos about using cover crops on this site. These were produced primarily for information about the value of using cover crops in no-till cropping systems although parts apply to tilled fields as well. If you do not have internet access, contact (717-840-7408) me for a copy on DVD.