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College of Food, Agricultural, and Environmental Sciences


Soybean Yields May Plummet in Absence of Rain

August 2, 2002

COLUMBUS, Ohio - Amid high temperatures and little rain, Ohio soybean growers are struggling to make lemonade out of a lemon of a crop, but their efforts may be fruitless.

Neither early-season nor late-maturing soybean varieties are escaping drought-like conditions that have been gripping the state since June. The outcome, predicts Ohio State University Extension agronomist Jim Beuerlein, may be a plummet in state average yields the likes of which growers have not seen in over 10 years.

"This year is probably the worst year we've had since 1988, where we were in a major drought and didn't hardly have any rain until late July or early August," said Beuerlein. "That year, state average yields were only 28 bushels per acre, 70 percent of normal. And to be honest, this year is stacking up to be just like that." He said that with the crop's poor performance throughout much of the state, average yields are likely to be no better than 85 percent to 90 percent of a normal yield. For each week fields go without rain, the number drops 10 percent to 15 percent.

"In terms of the crop's condition, you basically have to look at two halves of the state. Southern Ohio has received some rain so the crop is in much better shape. There, we are predicting yields to be normal to slightly below normal," said Beuerlein. "In the northern part of the state, it is extremely dry and continues to be dry. We probably aren't going to do better than 85 percent of a normal yield." Early-maturing soybean varieties are either flowering or have just completed flowering, but are setting few pods due to lack of rain. As a result, said Beuerlein, yields for such varieties, especially in northern Ohio, are going to be poor.

"We have about a week to a week and a half before the late-maturing varieties finish flowering. If we get rain, they should set pods fairly well," he said.

Several factors are involved that affect how much yield the soybean crop generates: the number of plants in the field; the number of pods per plant; the number of seeds per pod and how big each of the seeds will become.

"We have good stands, so we know plant populations are fairly high. But because of the dry weather, the number of pods per plant will be low. When those pods were set, we knew pollination was not good. So instead of averaging 2.5 seeds per pod, we may be down to two seeds per pod," said Beuerlein. "At this point, the thing we don't know is how big the seeds will get. If they grow large, that will lead to more yield. If we don't get any rain and they stay small, then we will have less yield." According to the Ohio Agricultural Statistics Service, as of the week of July 29, the state's soybean acreage is rated 28 percent to 37 percent in poor-to-fair condition and continues to deteriorate as time passes. This same time last year, the soybean crop was rated nearly 50 percent in good condition. Topsoil moisture is rated 44 percent very short, a 33 percent drop in adequate soil moisture compared to this time last year.

Beuerlein added that moisture deficit is much worse than numbers can convey.

"In the northern half of the state, the weather bureau has told us that we are receiving about one to two inches less rain than normal. But the deficit we are looking at is much worse than just what the numbers look like," he said. "We received all of the rain in the early months of the growing season and have received almost no rain in June and July, so there is absolutely no soil moisture. We are totally dependent on rain from here on out." In addition, the heat units, or number of suitable growing days, is also misleading.

"We are ahead by about 100 heat units. That's equivalent to five July days, but April was so cold that we didn't generate many heat units," said Beuerlein. "The extra heat the crop is receiving was all in July and with a lack of rain that's just two serious stresses on top of one other that are hitting the plants." To compound bad news on top of bad news, there is nothing a grower can do alleviate the stresses. "Irrigation may be an option, but all of the irrigation we have in the state is for our high-value crops like fruits and vegetables," said Beuerlein. "Planting other crops is not going to do much good without sufficient moisture, so planting something else is not going to be a salvation. Let's face it. We've run out of options. Our best hope is with the crop we've got." Ohio's corn crop is not faring any better. The Ohio Agricultural Statistics Service during the week of July 29, rated the crop 22 percent to 30 percent poor to very poor. This time last year, nearly 50 percent of the corn crop was rated in good condition. Lack of rain during the crop's pollination process is the cause for the crop's condition.

Severe drought stress before and during pollination may cause a delay in silk emergence, reducing kernel set whereby only the ears of the corn are partially filled. This ultimately results in low yields. Nearly 50 percent of the corn crop has silked, compared to 75 percent this same time last year.

Candace Pollock
Jim Beuerlein