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Corn+Soybean Digest

Experts Advise Cover Crops For Flooded Spots

The floods are over and the floodwaters have receded, leaving barren areas in many farm fields where crops were drowned out and not replanted. A large group of ag associations, agencies and Iowa State University (ISU) Extension are collaborating to inform farmers that they should consider planting cover crops on that bare ground to improve yields in 2009.

These once-flooded soils may be subject a condition called fallow syndrome, or post-flood syndrome. Experts say that the crop losses in following years to fallow syndrome can be dramatic, especially for corn. The impact could be significant with USDA estimates flooded and fallow ground at around 1.2 million acres in Iowa.

Fallow syndrome occurs when land is left unplanted for an entire growing season. Flooded soils will encounter problems caused by a reduction of beneficial soil fungi that are required for uptake of essential nutrients during the next growing season. Barren areas leave no place for these fungi to colonize and leave spores for the next growing season, so there is a yield drag until these fungi are reestablished in the soil.

There are also chemical and physical changes in flooded soils — floodwater can change soil aggregate stability, soil structure, soil pH and more. Bare ground is also more exposed to erosion and nitrate loss. The impacts, when totaled, can be significant.

A study on flooded soils released by the University of Wisconsin and Pioneer Hi-Bred International, Inc. showed that corn after fallow showed poor growth and as much as 15% reductions in yield. Cover crops can help mitigate that yield loss by improving soil quality and reestablishing biological communities.

Cover crops have added benefits. They are proven staples of conservation management systems, providing: erosion protection, nitrogen fixation, organic material, biodiversity, improved infiltration, aeration and tilth, food and cover for wildlife, weed suppression, forage and carbon sequestration.

Experts also advise farmers to consider planting cover crops in flooded fields before harvest. A September 15 deadline is suitable for most cover crops. For a fall cover crop that does not overwinter, oats, forage turnips, forage rape or radishes are probably good options. For cover crops that do overwinter, winter rye, winter wheat, winter triticale, and winter-hardy legumes will work.

Agencies and ag groups throughout the state of Iowa are cooperating to provide information to farmers. For more information on cover crops or fallow syndrome, visit or the NRCS at
For more information about cover crops, ask for the NRCS Conservation Practice Standard publication, “Cover and Green Manure Crop (code 340),” or the Iowa State University Extension publication “Small Grain Cover Crop for Corn and Soybean, PM 1999 and 2005.”

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