Heat, insufficient rain could hurt Indiana soybean crops

September 14, 2010

WEST LAFAYETTE, Ind. - Intense heat and lack of rain late in the summer has hit part of Indiana's soybean crop hard, likely leading to lower yields for some farmers even as a U.S. Department of Agriculture report forecasts the crop rebounding from a month ago.

Purdue Extension soybean specialist Shaun Casteel estimates the green plants in this field near West Lafayette were replanted about one month after the full-term beans because of flooding. (Purdue Agricultural Communication photo/Tom Campbell)

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Shaun Casteel, soybean specialist and assistant professor of agronomy at Purdue University, said Indiana's hotter- and drier-than-normal conditions during the first two weeks of August brought on heat and water stress, which could shorten the seed-fill period.

He expressed caution over the USDA's latest crop production report, released Friday (Sept. 10), that projects Indiana farmers will produce 264.5 million bushels of soybeans on a yield of 50 bushels per acre, up from last month's forecast of 259.2 million bushels and 49 bushels per acre.

Indiana produced 266.6 million bushels of soybeans last year on a yield of 49 bushels per acre. Although the per-acre yield could increase from 2009, the projected 2.1 percent decline in total production is the result of farmers planting fewer acres of the crop this year.

While crops being harvested now are producing strong yields because they were planted early in the spring, Casteel expects many of those planted later to show the ill effects of the dry weather.

"The ones I'm really concerned about are those that will be coming out in the next few weeks," he said.

With water stress, normal plant processes, such as photosynthesis and transpiration, will slow down. The soybeans will not be able to bring up nutrients through the plant, so the seed will not finish out to its potential. Also, the leaf cannot take in carbon dioxide because it is trying to hold onto water vapor as much as possible. As a result, maximum yield is reduced.

Heat stress and water stress is evident, especially in southern and northeastern Indiana, which are abnormally dry. While some parts of the state had hardly any rain in August, other areas had enough to give soybeans a chance to recuperate and catch up in growth.

Soybeans can withstand dry weather better than corn because they have a taproot system; they can dig deeper for water. Because of heavy rains early in the season, however, many plants did not develop deep roots.

"Adequate soil moisture during the early season deterred many roots from growing deep," Casteel said. "We didn't have any of the early-season deep water that would have forced the roots to grow deeper, whereas saturated soils limited plant growth and development, including the health of roots. The roots picked up all that they needed during early growth."

During August, the shallow roots could not pick up water that had penetrated deep into the soil, and the amount of water that was available closer to the surface was not enough to sustain the plants.

This stage of the season is critical for filling out soybean seeds. Without needed water, the seeds will not expand as much as possible.

"A smaller seed equals less yield," Casteel said. "The plants are going to abort pods or some seeds within a pod, and they can't get them back even if we have some rain a little later."

Soybeans in some fields have started to lose pods and seeds, he said.

Rainfall late in the season would help those crops that were replanted or planted late because they will be in the seed-fill stage and develop larger beans, Casteel said.

That rainfall could come, according to Ken Scheeringa, associate state climatologist.  He said there is a better chance for rain this month, while October may be similar to August with conditions drier than normal. This type of weather results largely from La Niña, a natural climate cycle in the Pacific Ocean that brought the extended dry weather.

"This is not necessarily bad news because farmers are harvesting and they won't be stopped by muddy fields," Scheeringa said.

The weather has been so dry that central and southern Indiana are approaching droughtlike conditions that might worsen, said state climatologist Dev Niyogi. While hurricanes in the Atlantic Ocean and Gulf of Mexico could provide some needed relief to Indiana, he said that prospect was unlikely in the short term.

Casteel said this could be a learning year for farmers as they assess pressures and stresses on their crops.  

Because the crop is maturing quickly, he said farmers should keep in mind that harvesting above 13 percent moisture can prevent yield loss.

Writer:  Elise Brown, 765-494-8402, brown222@purdue.edu

Sources: Shaun Casteel, 765-494-0895, scasteel@purdue.edu

                 Ken Scheeringa, 765-494-8105, kensr@purdue.edu

Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu
Agriculture News Page

Related websites:
Indiana State Climate Office

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