August rains rejuvenate drought-stressed soybean crop
July and August rains have come just in time to preserve some of the yield potential of much of Indiana's drought-stressed soybean crop, and more was on the way as the remnants of Hurricane Isaac moved north from the Gulf Coast.
While the season-long drought has not yet ended, rains and a letup in record-setting heat have combined to rejuvenate the crop so much that soybean farmers in some areas of the state could still see trend, or more normal, yields, Purdue Extension agronomist Shaun Casteel said.
But rain from Isaac over the long Labor Day holiday weekend might not be such a good thing for the crop, which could be damaged by flooded fields and wind. Rainfall amounts were forecast from 2 inches in the far north of the state to 7.5 inches in the south, according to the Indiana State Climate Office based at Purdue University (http://www.iclimate.org ).
"We could see some standing water in areas of the state that have been getting rain, where soil moisture has been replenished," Casteel said. "Soybeans in areas of the state that haven’t had much rain can still benefit from this weekend’s rain provided it is not excessive."
Most soybean plants are shorter than normal this year, so wind would not be as much of a factor as it would have been in other years. But as soybeans have recovered from drought stress, some have elongated internodes, or the distance between trifoliate leaves, and heavy pod production on the upper two-thirds of the plants. Those top-heavy plants would be most at risk for lodging, or stalk damage, from strong winds, Casteel said.
In its August crop production report, the U.S. Department of Agriculture projected that Indiana soybean yields would average 37 bushels per acre, down 24 percent from the trend prediction of 48.7. But those estimates were based on crop conditions as of Aug. 1, and if steady rainfall continues, Casteel said there's a chance growers could make up some of the difference.
"Late-July and early-August rains have helped soybeans retain pods, and more recent rains have helped the plants fill pods," Casteel said. "At this point in the growing season, we're keeping an eye on seed size."
The average size of Indiana soybean seeds is 3,000 seeds per pound. But as it rains, Casteel said that number from this year's drought-damaged crop could notch closer to 2,500 per pound.
Short plant sizes have alarmed many growers this season, but smaller plants don't necessarily equate to smaller yields.
"Plant stature isn't a driving factor in soybean yields," Casteel said. "What's more important is having plenty of leaf area. In a more normal crop, soybean plants would have 5-6 times as much leaf area as ground area, but good yields can be obtained with leaf area that is only four times the ground area."
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