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Fine tuning a cover crop system takes a minimum of three years.

Josh Flint, Editor, Prairie Farmer

February 24, 2012

6 Min Read

Last year, a lot of folks did everything right. The corn crop was in on time. The nitrogen was there. Everything looked good. Then it stopped raining.

For many in corn-on-corn situations, the end result was a well-below-average yield. Yet, there were stories of no-till cover-crop farms that saw hearty, 200-bushel yields. What gives?

Yield disparity is the primary reason many conventional farmers are taking a second look at cover crops. However, that yield difference may not always be there. Experts warn to not jump on the cover crop bandwagon with the expectation of a 20-bushel yield boost after one year. It's a process.

According to Pro Harvest Seeds' Doug Hanson, a Danforth, Ill., native, it's a three-year process. He advises clients to set three-year goals for a field, and then work backwards. That means identifying the cash crop and cover crop rotation for the next three years.

"If you want to be successful with cover crops, you've got to manage them like you do your cash crops," Hanson notes.

Building better soil

Pennsylvania research farmer Steve Groff warns expecting results after one year could lead to serious disappointment. However, those who stick it out see results.

Groff has seen significant advantages on his 225-acre research farm, just south of Lancaster, Pa. This year, Groff saw a total difference of 32.92 bushels/acre of corn between his cover-crop and control acres.

However, Groff says some of the advantages aren't directly related to yield. He's a big believer in the compaction reducing benefits of cover crops.

To prove his point, he placed two clods of soil in a sieve, which was immersed in water. The clod from the conventionally tilled field fell apart and settled at the bottom of the glass within a matter of seconds. The no-till, cover-crop clod was still sitting completely intact in the water an hour later when the demonstration was dismantled.

"In years where you don't see a yield response from cover crops, you're still adding to the soil bank account," Groff notes.

Erosion control, organic matter building, bio tillage and weed control are just a few of the benefits held in that bank account. Even if the first year doesn't produce noticeable yield results, Groff says folks need to understand they are creating fields that can be planted in wetter conditions without negative effects. Corn root systems will be able to push deeper. Reduced weed competition will produce better emergence.

For these reasons, many cover croppers struggle to pinpoint exactly why cash crop yields are higher. Still, researchers and farmers alike agree the benefits are synergistic. All are driving toward higher yields in the end.

Planting techniques

As with cash crops, planting and harvesting (or termination) of cover crops are key. Farmers aren't likely to forget the harvest that lasted through Christmas just a couple years ago. Though many probably believe getting a cover crop established in that sort of a fall is impossible, Pierceton, Ind., farmer Jamie Scott says aerial seeding can do amazing things.

On his farm, Scott typically drills as much as he can, which is about 200-400 acres. As the clock ticks down, he calls in for air support. Establishing the cover crop by October is paramount, he notes.

Last year, Scott coordinated a team of four planes to cover 4,000 acres in about 5 hours. "In years with late corn, that month head start is a big benefit," he says. "We want to get a cover crop established so it can scavenge nitrogen before it starts to leech out of the soil."

Scott uses a lot of annual ryegrass on his farm. In late October, the rye had only a few inches of top growth. Doesn't seem like a big deal, does it? When he dug a root pit, Scott realized his three-inch-tall rye had already put down a 24-inch root system.

Scott reports others in his area are beginning to experiment with cover crops. In 2011, Scott's neighbor averaged 115 bushels/acre on his conventional corn. His cover-crop/corn acreage averaged 153 bu./acre.

Termination tips

Watching a cover crop grow to mammoth proportions in the spring can lead to a mammoth disaster, says conservation specialist Mike Plumer, who spent 34 years with the University of Illinois before retiring.

Before the burndown window nears, Plumer says the farmer needs to understand why the cover crop is there in the first place. Is the primary reason to build nitrogen levels, create root growth for bio tillage or suppress early-season weeds?

Most grass varieties max out on root growth in the first two weeks in April. "As soon as a grass joints, it's usually done with root growth," Plumer notes.

If available N is the primary goal, the trick is waiting for the legume plants to get fairly large, but terminating it before it reaches the reproduction stage. For example, Plumer says 90% of hairy vetch's nitrogen content is in the top growth. Once hairy vetch blooms, it's reached its full N potential. After hairy vetch blooms, simply walking on it will kill the plant, so control is very easy, Plumer notes.

The further the grass plants get into the reproductive stage, the longer it takes for the nitrogen to be released in the soil, since the plant has to break down, Plumer explains. For grasses, much of the nitrogen becomes available in the vegetative stage of growth. Once the plant reaches first joint, the nitrogen becomes tied up in the plant and will release as the plant breaks down over the course of a year or longer. The same is true once legumes reach the bud stage. Waiting longer only increases the amount of time it takes for the plant to release the available N.

As a rule of thumb, Plumer says annual ryegrass typically joints at 7 to 10 inches, which can be between March 15 and April 20. When spraying hairy vetch, Plumer recommends killing it in the vegetative stage for both ease of control and nitrogen release. A week after spraying vetch, it will be brittle enough that row cleaners will shatter it rather than collec it. Plumer learned this the hard way, when he had to remove 100 pounds of vetch from the row marker after each pass.

As with typical weed control, Plumer recommends using multiple modes of action when burning down cover crops. Also, he warns a complicated blend of cover crops can mean trouble when mixing up a concoction that will control them.

Most importantly, Plumer says to spray on time. "You've got to be ready to spray no matter the condition," Plumer adds. On his research fields, he uses an ATV sprayer. "There is no reason for a farmer to wait with an ATV sprayer," he notes.

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