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August 2, 2002

Indiana soybeans lamenting, 'How dry I am'

WEST LAFAYETTE, Ind. – Indiana soybean farmers are hoping it rains on their parade – and fast.

Soybean crops are entering an important growth phase. In August, plants usually begin developing pods and filling them with seeds. Unfortunately, many soybean fields aren't getting the moisture necessary to progress, said Ellsworth Christmas, Purdue University Cooperative Extension Service soybean specialist.

"It depends on where you're at in the state as to the condition of the crop," Christmas said. "In west central Indiana, we've had good rainfall over the last month, and those beans are growing very rapidly and developing very nicely. If weather conditions continue, we're looking at a very respectable crop.

"If you move to eastern Indiana, it is relatively dry. Those beans are under tremendous stress. They're still very, very short, the plant canopy has not closed, and with the moisture stresses that we have we're seeing quite a bit of floral – and some pod – abortion in those fields."

The condition of Indiana soybean acres is slipping week by week, and with it the potential for normal yields. In its most recent crop report Monday (7/29), the Purdue-based Indiana Agricultural Statistics Service (IASS) downgraded the state's soybean crop. The IASS reported 35 percent of soybean acres were in "good" to "excellent" condition, compared to 39 percent the previous week, and 72 percent at the same time last year. Twenty-seven percent of the crop was rated "poor" or "very poor."

Inadequate rainfall is blamed for much of the crop stress. Many counties in northeast, north central, central, east central and southern Indiana received less than an inch of precipitation in the final weeks of July.

Soybeans, like corn, need an inch of rain per week during critical growing phases, Christmas said.

"It's not too late to turn this crop around," he said. "We still have time for those beans to flower and set pods, but we need the rains rather quickly for that to occur. If we do have rain, we're going to need the rain to carry through to at least the second week of September. We normally say August, but with the late planting of this year's crop we need rain through the first two weeks of September to give us a reasonable yield."

Because the crop was planted weeks behind schedule after a wet spring prevented many farmers from getting into their fields, most soybean acres are just now blooming. The IASS reported 58 percent of soybean acres were in bloom as of July 28, well off the 2001 pace (92 percent) and five-year average (82 percent). Just 16 percent of soybean crops were setting pods, compared with 47 percent the year before and 35 percent for the five-year average.

Soybeans begin setting pods at reproductive stage 3, with pod development completed in stage 4. Seed fill takes places in stages 5 and 6.

"Yield is determined by the number of pods for a given area, the number of seeds in those pods and the weight of the seed within the pod," Christmas said. "Stresses at reproductive stages 3 and 4 can reduce the number of pods. Stresses at reproductive stages 5 and 6 can reduce the number of seeds within the pod, and also can reduce the size of the seed. If any one of those things occurs, it'll have a negative impact on the final yield."

Dry conditions are hurting soybeans in another way. Spider mites and soybean aphids, two deadly soybean pests, thrive on hot, parched crops. Farmers should monitor their fields for outbreaks of either pest, Christmas said.

Nutrient deficiency also is a problem in certain areas, Christmas said.

"I've had some reports recently of a lot of fields that tend to be yellowing," he said. "Under those conditions I'd look for two things. First of all, I'd look for the possibility of soybean cyst nematode that may be restricting the root system, particularly if the deficiency symptoms appear to be a potassium deficiency.

"The other element that's causing this is manganese deficiency. It tends to be more severe on our sandier, well-drained soils. If deficiency symptoms appear, about the only solution is an application of one pound of elemental manganese per acre, as a foliar application."

Indiana farmers planted an estimated 5.7 million acres of soybeans this year, up 2 percent from 2001, according to the IASS. The soybean acreage is the most planted in state history, and marks the first time Indiana farmers are growing more soybeans than corn. Farmers planted an estimated 5.4 million acres of corn, the IASS reported.

Indiana produced a state record 273.9 million bushels of soybeans in 2001, at an average yield of 49 bushels per acre.

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: Ellsworth Christmas, (765) 494-6373, echristmas@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

Related Web sites:
Purdue Agronomy Drought Stress Information

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


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