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Thirsty, stressed crops tapping hidden soil moisture

Agriculture.com Staff 06/26/2007 @ 12:48pm

Despite some recent showers, drought-like conditions continue across Ohio and field crops are beginning to exhibit signs of stress. At the moment, however, enough soil moisture is still available for the crops to get by.

According to the Ohio Agricultural Statistics Service, soybeans and corn remain over 70% in fair to good condition, despite the fact that topsoil moisture is nearly 80% short to very short. But the stresses from the lack of prolonged, adequate moisture are beginning to take a toll on the state's major crops, especially corn.

Peter Thomison, an Ohio State University Extension agronomist, says in a university report that corn in areas of the state is beginning to roll, an early symptom of drought stress. The plant rolls its leaves during mid-day as a defensive mechanism to reduce photosynthesis and conserve water.

"Corn plants with leaf rolling during early-to-mid vegetative development may look severely stressed, but it's usually cosmetic and has no long-term impact on yields," says Thomison, who also holds a research appointment with the Ohio Agricultural Research and Development Center. "Yield losses to moisture stress are directly related to the number of days that the crop shows stress symptoms during different growth periods."

He says drought stress during early vegetative growth usually has a negligible impact on yield, but as the corn develops and begins to form ears, drought conditions will have more of an impact on the plant.

"The number of kernels per row on an ear will be affected more by stress than the number of rows on an ear," says Thomison. "During the late vegetative stages, drought stress can reduce yields five percent to 10%. However, severe water stress during tassel emergence can reduce yields up to 25%, and during pollination it can reduce yields up to 50%."

A current condition of corn that can have a direct impact on yields is uneven plant emergence. Thomison said that corn some fields are exhibiting extreme height variations -- for example corn that is five inches tall growing next to corn that is 20 inches tall.

"As much as 30% or more of the corn crop is experiencing some level of unevenness," says Thomison. "This situation could have an impact on yields later in the season because late developing plants can't compete with those more developed. Later developing plants don't have a well-established root system to combat the stresses later in the season, and they are also more susceptible to insects and diseases."

Despite the potential troubles facing the corn crop, soil moisture is keeping it going -- for now.

"We've got good soil moisture four to seven inches deep in the soil. If the roots can reach that far, the crop for right now is still doing okay, based on observations of the crop in my region," says Harold Watters, an OSU Extension educator from Champaign County. "Any lack of significant rainfall after the 4th of July holiday may place the crop in critical condition. But we've had instances in the past where we haven't seen any good rainfall until August 1, and we still made some recovery."

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