30 THERE WAS LITTLEmoisture to spare through June and the first half of July. How prolonged dry conditions will affect corn and soybean yields this fall will vary based on drought tolerance, the severity of drought conditions at specific planting stages, soil type — and, as always, a little luck. THE BROADER PICTURE Providing an overall assessment of Ontario’s corn and soybean crop is often fraught with exceptions and contradictions. For Ben Rosser, corn specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, provincewide statements are even more difficult this year since what rain has fallen has been fairly sporadic. Painting very broadly, though, reports to mid-July (the time this article was penned) suggest eastern Ontario has been comparatively lucky in terms of moisture accumulation. The southwest has experienced many rain pockets but nothing of wider significance. Rosser says conventional extension indicates early drought stress such as that experienced in June results in a fairly minimal negative impact on corn. Similarly, Drought conditions IMPACT ON CORN AND SOYBEANS Matt McIntosh DROUGHT STRESS IN CORN. yield impacts again drop off around the grain fill period. Dry soil at tasselling is the real problem. “We’re in the rapid growth phase now. If you’ve got evidence of drought stress, it’s becoming more of an impact on yield,” Rosser says, speaking on July 14. Soybeans are a different situation. Adequate moisture is most critical during the pod fill period and to a lesser extent during earlier R stages, making dry conditions in June and the first half of July less concerning. Moisture accumulation after mid-July will have the biggest impact. Less concerning doesn’t mean no concern, though. According to Iowa State University, early season drought can affect growth by causing leaf trifoliates to close. “Under severe drought stress, soybean flowering may occur earlier than normal in an effort to produce seed before premature death… Drought can reduce pod number by up to 20 per cent as a result of flower and pod abortion. Seeds per pod and seed size can also be affected by drought stress but to a lesser extent than the number of pods.” GENETICS AND SOIL QUALITY Soils with higher moisture holding capability are of particular value in parched conditions, says Rosser. He cites the similarly dry conditions experienced in 2016 and 2020 as recent examples where crops growing in lighter or less healthy soil were visibly more stressed. “In those years, we started to get some rainfall over [the second half of July], and things had replenished by tassel time…we had really strong yields in both those years,” he says, adding a lack of rainfall has likely contributed to lower disease progression this year. Agronomy
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