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Cover crops: Not just a plant anymore

By Staff | Apr 12, 2013

AJAY NAIR, an ISU professor of horticulture, discusses cover crop benefits with Jan Hollebrandts, of Polk County, during an April 5 cover crops meeting in Mason City. The plants are samples of cover crops that do well in Iowa.

MASON CITY – Jesse Huang, of North Iowa Berries and More, of Mason City, said he was looking for tips in working in cover crops among his business’ vegetable rows.

Jan Hollebrandts, traveled up from Polk County, to learn more about cover crops in general, and specifically ask how to encourage her renters to plant cover crops and switch to reduced tillage methods.

Huang and Hollebrandts were among about 30 people attending a cover crops event with a twist – for fruit and vegetable operations.

Ajay Nair, an ISU horticulturist, said all farmers, whether growing commodity row crops, fruit or vegetables must adopt a different mindset about using cover crops.

Instead of thinking of cover crops as something to spread over a field, Nair said, “They need to see cover crops are part of the cash crop operation, so it takes some management.”

“They need to see cover crops are part of the cash crop operation, so it takes some management.” —Ajay Nair ISU professor of horticulture

Andy Lennsen, an Iowa State University professor of agronomy, provided an overview of what Iowa researchers have learned about cover crops in the past several years, followed by:

  • A discussion on using cover crops in fruit operations, by Gail Nonnecke, an ISU professor of horticulture.
  • A presentation of using cover crops in vegetable systems, by Nair.

No perfect cover

In general, Lennsen said, cover crops protect the soil, which stands bare for seven months of the year, from wind and water erosion, as well as supply organic matter and lock nitrogen in place, keeping it from leaching out in fall and spring rains.

Covers provide additional nutrients and offer improved weed management. They work best in reduced-tillage systems.

Specifically, however, “there is no perfect cover crop. Different covers work best with certain soil types, slopes and tillage systems.

“They lock in nitrogen, but they also use it,” he said. “If they are allowed to grow too long, they may use up valuable moisture.”

He said researcher have found a corn disease in the radical root following a cereal rye cover, and determined that corn was seeding too soon after the crop was burned down. As the cover deteriorated, the excessive amounts of nutrients being released, burned the corn roots.

He said in test plots, where corn was planted three days after killing winter rye, 83 percent of the radical roots were diseased, probably by rhizatonia bare patch.

However, he said, waiting 10 to 14 days after killing the cover, there were fewer problems.

Lenssen acknowledged that it is more challenging to work cover crops into a row-crop rotation in the Upper Midwest due to the shorter growing seasons.. He advised producers to read cover crop research that was performed in Region 5 cropping zones.

Fruit systems

Nonnecke said cover crops provide fruit planting with benefits, but also can pose problems if not closely managed.

Aside from providing some weed and pest control, she said certain cover crops are believed to suppress populations of parasitic nematodes, while encourage the proliferation of beneficial nematodes.

She offered tips for selecting cover crops in strawberries, orchards and with nonbearing fruit plants in dormant stages.

Creeping fescue, she said, have been used as a living mulch under grape vines, and mowed sorghum-Sudangrass between rows of strawberries.

In Granger, test plots found white Dutch clover encourage growth of more raspberry canes and increased yields when used as a living mulch.

Vegetable systems

One of biggest benefits of cover crops in vegetable systems, said Nair, is covers add nutrients to existing plant food in soils, requiring growers to add less compost.

Cover crops can have been used as windbreaks to protect more delicate plants, like lettuce, Nair said.

A primary challenge for growers, especially planting non-legume covers, such as winter rye and annual ryegrass, is that if left too long, they can go to seed and become a weed.

Legume cover crops, including many of the clover species, provide a free source of nitrogen for plants, Nair said.

Red clover, Nair said, has been found to provide 50 to 120 pounds of N per acre, followed by hairy vetch that adds 50 to 100 pounds of N per acre.

By contrast, soybeans add 40 to 100 pounds of N per acre

Brassica cover crops – yellow and brown mustard and oilseed radish – provide a biological fumigant to control pests, suppress parasitic nematodes and reduce compaction due to their strong taproots.

Brassicas, Nair said, are a biofumigant plant, meaning that when their cell walls are opened, through mowing, they release both myrosinase and glucosinolate that forms an isothyiocyanate, which is the biofumigant.. “But you have to mow it,” Nair said, “before incorporated into the soil.

Oilseed radish, he said, proved in test plots to provide the best reduction of parasitic nematodes, about 60 percent compared to the control plot; while advancing bacterial nematode populations by 300 percent over the control plot.

Yellow mustard will attract pollinators for flowering vegetables, Nair said.

Vegetable growers should consider using a cover crop during the dormant weeks of harvesting spring crops and planting fall crops, he said.

The daylong meeting was co-sponsored by ISU Extension for Cerro Gordo and Mitchell counties, plus the U.S. Department of Agriculture-National Laboratory for Agriculture and Environments, and by the Leopold Center for Sustainable Agriculture.

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