Impacts of southwest Michigan drought on 2013 corn and soybean yields

The lack of late season rainfall is taking luster off of crop yield expectations across much of southwest Michigan.

As the old saying goes, “It ain’t over until it’s over.” While this adage is certainly true for football games, it also looks to be true for the 2013 growing season in the southern two tiers of counties in southwest Michigan. Despite an abundance of rainfall across many areas of the state over the last couple of weeks of August, including an hour delay in Michigan State University’s home football opener last Friday night (Aug. 30), portions of southwest Michigan have slipped into a significant drought, putting commercial corn and soybean yields at risk at the 11th hour before harvest.

Many fields were progressing rapidly towards physiological maturity when the drought stress began. Until corn reaches black layer and the upper pods reach mature pod color, the crops can be damaged by dry conditions. In soybeans, dry conditions during the R6 growth stage can cause yield losses through seed abortion, pod abortion and smaller soybean size. Severe stress reduces the time that the plants remain in this important growth stage for yield.

Irrigation systems have been running “overtime” to try to provide enough moisture to help the plants to move sugars to maturing beans and corn kernels. Michigan State University Extension educator Lyndon Kelley reminded growers in his recent article “Late planting and early season cool weather may have producers irrigation into September” that it is important to maintain soil moisture levels above 40 percent available soil moisture to allow the plants to reach physiological maturity. He also noted that it is much easier to accomplish this goal at this point in the season, since evapotranspiration rates are less than 15 percent of what they are during peak water usage.

How much yield loss should growers with drought-impacted fields expect due to this late season deficit? It will depend upon the growth stage reached before the drought occurred and how severe the soil moisture deficit has been in your area. While the cooler temperatures will help reduce stress to some degree, the bright sunshine continues to drive plants to transpire water at higher levels than is normal for this time of the year. Areas in corn and soybean fields where water may have run off due to slopes have simply dried up and the plants have died, while areas of the field with adequate moisture remain green. Corn that is stressed before the plants reach physiological maturity tends to have poor test weights and can be tricky to dry and store. Soybeans that mature under drought stress are smaller, which reduces yield. Maturation under these conditions can also lead to uneven crop dry-down, which can lead to shatter losses in the early senescing areas of the fields. It is important to recognize that from a potential yield-limiting standpoint, late season stress is much less damaging than severe stress during pollination and early grain-fill for corn. At this point, it is likely that we have removed between 10 to 15 percent or more of yield potential from what had previously looked to be an excellent crop.