July drought and soybean prospects
The same plant from Perry, with the view enlarged to show the failure of pod formation on the lower nodes. As the number of "spent" racemes continues to increase under stress, pod number, and hence yield potential, will continue to decline. New racemes and pods that will form with rain can help to overcome some of this loss, but the lack of a full canopy will also limit the number of pods that can be filled. As is the case with corn, sugar supply in the soybean plant will ultimately determine yields. When the supply is short during flowering, pod numbers decline; when the supply is short during pod filling, then pods will drop early or, if they manage to stay on, seed size can be reduced.
Later-planted soybeans retain more flexibility in raceme, flower, and pod number compared with those planted early. This means that a return to better conditions may help the later-planted crop more than it helps early-planted soybeans. On the negative side, later-planted soybeans are even shorter, with fewer nodes than early-planted ones, and the root system is likely not as extensive as in the early-planted crop. But if stress is relieved by late July, it is possible that later-planted soybeans might set more pods and produce more yield than those planted in April.
click image to zoomRacemes on upper nodes of a soybean stem. To some, it might seem reasonable to try to protect yield potential through applications of fungicides, insecticides, and perhaps other products that promise to "relieve stress" in soybean crops. But when lack of water is such an overwhelming factor as it is in 2012, it is unlikely that any inputs (other than irrigation) will do much to help. While it is important to scout for and manage pests that can add to stress, there are few data showing that a crop under severe stress can have its physiology and yield potential improved by additives of any kind.
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