Cover crop questions
Southeast Iowa farmer Tim Sieren and his family run a small, diversified farm raising corn, soybeans, hogs, cattle and small grains. He added cereal rye into the cropping system as an additional source of forage for his cattle. After seeing the soil benefits, he started using it as a cover crop between no-till soybeans and corn. Now, he plants cover crops on all of his acres.
Sieren, a member of Practical Farmers of Iowa, has conducted on-farm research on a number of cover crop topics. For more information on his and other on-farm research, visit . Here, Sieren answers common questions that row-crop farmers new to cover crops have.
What effect do cover crops have on cash crops? Cover crops have many effects on cash crops; unfortunately it takes several years for most of them to show up. The biggest and first benefit from year one will be erosion control. A fall-seeded cover crop that germinates before freeze-up and is able to survive the winter will be right there when the weather warms up in spring to start growing, no matter what the weather brings. If allowed to grow as long as possible, the cover crop will sequester nitrogen left in the soil from the previous crop and hold that N for the next crop.
Other benefits include increased soil tilth and structure, reduced soil compaction, reduced surface crusting, winter annual weed suppression, and moisture retention. Other benefits that take a few years to realize are increased soil organic matter resulting in more N-P-K availability, increased biological activity (including earthworms), reduction in crop residue issues, improved soil drainage, and increased crop yields, not to mention cleaner water leaving your fields, as well as less nutrient loss to help keep the environment cleaner.
Some problems that can show up are increased insect, rodent and wildlife pressure; increased or decreased soil moisture, depending on weather conditions; extra cost of seeding and termination; extra time and labor for seeding; allelopathy effect on the following crop if not terminated on time or if the carbon-to-nitrogen ratio is out of balance; and volunteer plants showing up in following years if not terminated properly.
Which cover crops should I choose to plant? You need to decide what you want the cover to do before selecting cover crops. You can choose covers for all the benefits listed above. It also depends on planting date of the covers selected. A good seed dealer can help with this selection process. There are also several websites and YouTube resources available.
If you want a cover after row crops, one that’ll survive winter, you are limited to a fall-seeded cereal, such as wheat, triticale or cereal rye. There are some brassicas that have some winter tolerance, such as winter canola, rapeseed, kale and some legumes, including winter peas, hairy vetch and clovers. In general, brassicas are used for forage and soil compaction reduction, as well as N sequestration. These include tillage radish, turnips, canola, kale and rapeseed, among others.
For soil-building properties, N scavenging and erosion control, grasses with fibrous roots are used, such as rye, oats, barley, triticale, wheat and annual ryegrass. Legumes such as peas, vetch, clover and beans are used for fixing N for the next crop and as forage. Specialty cover crops are also used as wildlife food plots, pollinator habitat and biofuel. Farmers seeding covers for the first time should start with cereal rye. It is easiest to get established, grows fast, is winter-hardy, provides most benefits and is easy to terminate in spring.
How much time does it take to benefit my soils? You will benefit from erosion control the first year, and progressively increased water infiltration every year after. The soil-building properties will take several years to see results. Cover crops are a lot like no-till farming: The longer you do it, the better it gets. You’ll see increased soil health in three to four years. No-till magnifies the results as well. If you have livestock or manure, you can benefit even more.
If you are determined to do fall tillage, cover crops are a waste of time and money. Cover crops need to be seeded shallow, and fall tillage will dry out the soil for reduced emergence. If you seeded a cover crop in late summer or early fall to eliminate compaction, fall tillage would undo any benefit that was gained.
Full-width spring tillage is not compatible with cover crops either. If you till a winter-hardy cover crop in spring, it will regrow, unless it’s plowed completely under, like some organic farmers do. Tillage negates any biological activity by breaking up bacterial and fungal colonies, releasing carbon to the atmosphere, as well as eliminating the erosion protection.
Cover crops need to be terminated as late as possible, to get the maximum benefit from them. If you’re the early-bird in the neighborhood, who has to plant corn the first week of April, don’t even consider cover crops in the Midwest, because they won’t get enough growth to provide any benefits.
How and when do I get a good stand established? Timing of planting depends on the species and method of planting. If you are seeding a winter-hardy cover crop, you can have the seed flown on by airplane any time after the row crop starts to mature and turn brown to open up the canopy for the seed to hit the ground, usually around mid-September.
After the cash crop harvest, winter wheat can be seeded up until mid-October, and cereal rye can be seeded successfully until mid-November, or freeze-up. Fall-seeded covers can be seeded with a drill or air seeder, broadcast seeder, or fertilizer spreader. Any way to get a fairly even spread will work; then follow with a light harrow or vertical tillage pass.
Some farmers are using Gandy air boxes on their vertical-tillage implements, or they use broadcast setups on their high-clearance sprayers. The main requirement is to get good moisture for seed germination. If using brassicas or legumes, summer seeding works best to get at least six weeks of growth before frost. This could be after seed corn, silage, oat or wheat harvest. A no-till drill works best in summer to seed deeper into moisture for best emergence.
How and when do I terminate? There are four ways to terminate cover crops:
• Winter kill. Frost will kill any covers that are not winter-hardy, such as oats, radishes, turnips, peas and beans.
• Spring chemical burndown. This includes glyphosate, gramoxone, Liberty and other herbicides, depending on the crop being terminated.
• Spring tillage. This is usually a green manure plow-down pass, mainly used by organic farmers.
• Roller-crimper. This is a large roller with cleats that rolls down the cover crop and crimps the stems, so it lays on the ground and dies.
Spring termination should be as late as possible, yet still keep you in the optimum planting window for the subsequent cash crop, such as corn or soybeans. This timing will get the maximum growth and benefit from the cover crop. If a spring-seeded cover, such as oats or barley, is being terminated, it should be done before the cover goes to seed, because that’s when the organic matter is at its peak. After heading, the plant puts its energy into the reproduction stage and organic matter production starts to drop off.
Ohde writes for Practical Farmers of Iowa, based in Ames.
This article published in the February, 2016 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2016.