cover crops

Keith Berns discusses cover crop species during a soil health workshop Wednesday in Burley. Berns is co-founder of Green Cover Seed in Bladen, Neb.

BURLEY — Jay Fuhrer used to think cover crops were important for building soil health. Now he thinks they are critical.

Fuhrer is the soil health specialist for the USDA Natural Resources Conservation Service in North Dakota. He was in Burley as part of the fifth annual soil health sustainability workshop sponsored by the conservation districts in Cassia and Minidoka counties.

Keith Berns echoed Fuhrer’s assessment. Berns co-founded Green Cover Seed with his brother 10 years ago after they began to see the benefits of cover crops on their farm in south-central Nebraska. Their 2,500-acre farm has been in continuous no-till for 25 years.

He’s seen farmers who include cover crops in their rotations increase organic matter in their soil by 0.1 percent annually. Over 10 years, that adds up to 1 percent organic matter. Given that soils in southern Idaho are often around 2 percent, a 1 percent increase is significant.

On his own farm, Berns has seen that fields with higher organic matter are the last to show signs of drought or to suffer pest problems.

Cover crops also increase diversity both above and below ground. Many farmers include legumes in a crop rotation because legumes are nitrogen fixers. These plants are associated with rhizobium bacteria which can turn atmospheric nitrogen into plant available nitrogen.

Raising an 80 bushel-per-acre soybean crop in Nebraska requires 700 pounds of nitrogen per acre. Farmers can’t afford to put that much nitrogen on a crop, but the rhizobium can crank out 700 to 800 lbs. of nitrogen within the growing season.

Rhizobium are the rockstars of nitrogen fixers but other free-living organisms such as azotobacter and azosprillium can also “fix” nitrogen, just not as much. These organisms don’t live in large colonies like rhizobium and so they only contribute 20, 30, maybe 40 lbs. of nitrogen to the system.

While 30 lbs. of nitrogen may not do much for a soybean crop, it makes a huge difference for a cover crop or a grazing forage. But those organisms won’t go to work if there is excess nitrogen available in the soil.

“Plants aren’t stupid,” Berns said. “They will do whatever is cheapest and easiest.”

Cover crops provide food and habitat for mycorrhizal fungi that colonize plant roots. The plant feeds these fungi with a liquid carbon exudate formed through photosynthesis and in turn the fungi bring nutrients and water to the plant.

Berns calls mycorrhizae miners in the soil. Phosphorus, for example, is one of the hardest nutrients for a plant to get out of soil. But mycorrhizae can help break apart chemical bonds that make phosphorus unavailable to plants.

It’s these kinds of symbiotic bonds between plants and organisms that make soil biology work, but it all begins with diversity.

Rob Giesbrecht, who farms in eastern Idaho, has been including cover crops into his wheat and potato rotation for 20 years. He said cover crops make the principles of soil health work.

When farmers ask him about using cover crops, Giesbrecht encourages them to figure out what problem they are facing in a specific field and then attack that problem. A cover crop specie that works for him may not work for a neighbor because the problem is different.

“Take the time to figure out how to make it work. You’re a farmer, you deal with problems every day,” he said.

Failure is OK, he added. Sugar beet growers lose fields every year because of wind or frost. That doesn’t keep them from planting sugar beets.

Giesbrecht focuses on building soil health during the years when a field is not in potatoes by utilizing no-till and cover crops with his grain crops.

He agreed with Berns advice: more is better than less but something is better than nothing.

“Develop your own soil health toolbox,” Giesbrecht said. “Once you figure out yours, you will use it every day.”

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