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Nitrogen Timing Key for Cover Crop Success

Take steps to ensure nitrogen is available for cash crops.

If you want an indicator of how quickly the soil health movement has grown, get this. In 2009, Keith Berns and his family grew cover crop seed just on a small scale on their Bladen, Nebraska, farm. Today, their business, Green Cover Seed, sells enough cover crop seed to cover 850,000 acres. 

“No-till by itself is good, but when we add cover crops, we add living root channels and stimulate earthworm activities,” he says. Berns told those attending this week’s Iowa State University Soil Health Conference that this helps farmers better manage water on top of curbing erosion and rebuilding soils. Managed properly, he says cover corps can also raise yields. 

A 2016-2017 annual survey of 2,012 farmers conducted by the Conservation Technology Information Center (CTIC) with help from Purdue University and funding support from Sustainable Agriculture Research & Education (SARE) and the American Seed Trade Association (ASTA) reported that after cover crops: 

  • Corn yields increased an average of 2.3 bushels per acre, or 1.3%
  • Soybean yields increased 2.1 bushels per acre, or 3.8%
  • Wheat yields increased 1.9 bushels per acre, or 2.8%

“If you understand the system and apply (proper) management strategies, that is when you will see yield increases,” he says. 

However, that’s not always a given. He quotes Steve Groff, founder of Cover Crop Solutions from Lancaster, Pennsylvania, who has said, “Cover crops make a good farmer better and a bad farmer worse.”

Nitrogen Timing 

One mistake Berns sees concerns nitrogen (N) application and how it relates to cover crop termination. 

“It’s not necessarily the timing of the termination of the cover crop (in the spring before or shortly after cash crop planting),” he says. “The mistake they make is when they apply nitrogen. If they apply it in the fall or early spring and let (cover corps) rye or oats or barley get fairly tall, they can start to lignify. The carbon/nitrogen ratio goes up, and that N that they apply will be tied up in the plant material. It’s not lost, it just takes longer to cycle through.” 

Thus, the N can be tied up in cover crop plant material when the corn crop needs it the most. 

“I’m not saying there’s a right or wrong way to terminate it (cover crops),” he says. “On our dryland acres, we terminate them early because we need to conserve moisture to get our crops up and going. On irrigated crops, we will let the rye get 4 to 5 feet tall before we plant our soybeans. We have even done it on corn.” 

Rarely Too Late

“Another mistake is sometimes people wrongly assume it’s too late to plant cover crops,” Berns says. He concedes that it can get too late after a long-drawn-out corn harvest.
Still, cereal rye is an exception that can often be planted in the fall.

“Cereal rye germinates in 34˚ soil temperatures,” says Berns. “All it has to do is sprout. If you get it to sprout, it will (then) vernalize and come screaming out of the ground and outgrow marestail, henbit, wild mustard, all of those winter annuals.”

They’ve had success planting cereal rye in some years even into mid-December. “So if you can get a drill in the ground, there is still an opportunity to plant cereal rye,” he says.

Water-Management Benefits 

Cover crops are a tool farmers can use to successfully manage water, says Berns. They can help boost infiltration from less raindrop impact and create more root channels, conserving 2 to 4 inches of water annually. Cover crops can also key less evaporation during the growing season, saving another 2 to 4 inches of water annually.

That may be little help during a wet year, but during a drought year, benefits can be large, he says. In 2012, corn yield spikes of 12 bushels per acre resulted when cover crops were used, he says. 

Cover crops can also be used to manage water in wet springs. Last year, he visited the farm of Trey Hill, Rock Hall, Maryland; it plants into standing cover crops.

“The number one reason they use cover corps is it makes planting easier for them,” says Berns. “In Maryland, they are wetter than we are. They can be out planting green when the fields are wet.” Hill then comes back and terminates the cover crop mix shortly after planting.

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