Experts Advise Cover Crops for Flooded Spots

They say you can get improved yields next season, but you need to plant before September 15.

The floods of 2008 that struck many parts of Iowa in June have left barren areas in many farm fields where crops were drowned out and not replanted. ISU Extension agronomists and conservation specialists with USDA's Natural Resources Conservation Service are advising farmers they should consider planting cover crops now on that bare ground - to improve yields in 2009.

These once-flooded soils may be subject to a condition called "fallow syndrome" or "post-flood syndrome." Experts say that the crop losses in the following years, caused by fallow syndrome, can be dramatic - especially for corn. The impact could be significant this time around, as USDA estimates flooded and fallow ground at around 1.2 million acres in Iowa in 2008.

What is fallow syndrome anyway?

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 re-established 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.

Consider the benefits of cover crops

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 re-establishing biological communities.

Cover crops have added benefits, too. 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.

Should plant cover crop by mid-September

ISU agronomists also advise farmers to consider planting cover crops in flooded fields before harvest. A September 15 deadline for planting is recommended for most suitable 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 in Iowa are cooperating to provide information to farmers. For more on cover crops or fallow syndrome, visit or 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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