Many farmers were praying for rain by June 20. Some of you got it, and some didn’t. Even if your fields got rain and perked up after a dry stretch, will there be any lasting impacts from early-season dry weather when you run the combine this fall?
Bob Nielsen’s answer may sound like he’s ducking the question, but the Purdue University Extension corn specialist insists that he is just laying the cards on the table. “The best we can say is that it depends,” Nielsen says.
The U.S. Drought Monitor showed a good portion of Indiana was “abnormally dry” in mid-June. That’s the first step on a rating scale that progresses all the way to “extreme drought.” If you want to know what that looks like, think 2012.
Early-season dryness in June can be a plus, resulting in deeper rooting and better uptake of moisture later in the season, Nielsen notes. However, that assumes roots weren’t thwarted by compacted layers during the dry period, and it also assumes significant moisture returns before drought stress becomes serious.
The question of whether dry weather early impacts yield later hinges to some degree on timing.
“If soil near the surface becomes excessively dry when initial nodal roots of V2 to V6 plants are developing, the young roots may dry out and die,” Nielsen says. “That’s when you see floppy corn syndrome, when plants literally fall over due to lack of roots. If it’s severe enough, you can lose population. That would likely impact yield.”
Severely dry soils early in the season, coupled with warm, sunny days, can limit water uptake enough to affect photosynthesis, Nielsen says. You see this as plants roll their leaves when leaf stomates close to slow transpiration. While losing less moisture helps the stressed plant, the agronomist notes that closed stomates result in less carbon dioxide taken into leaves. That’s not good because it reduces photosynthesis, he adds.
Leaf rolling and reduced photosynthesis, if severe and prolonged, can stunt plant development, resulting in shorter plants or smaller leaves. It can also restrict ear size potential by impacting ovule formation during corn’s rapid growth period. In a truly severe, continuous drought, plants may outright die, Nielsen says.
The bottom line is that there are several ways that early drought impact can affect yield, he summarizes. Loss of plant population per acre would affect yield directly. Reduced ovule formation before pollination would have a negative impact. So would loss of surviving kernels after pollination through abortion of young kernels and decreased kernel weight during grain fill.
Decreased kernel weight during grain fill could happen if plants are smaller due to early-season impacts. That means the overall photosynthetic factory is smaller.
The bottom line is that the overall impact of early-season dry weather stress truly depends, Nielsen emphasizes. It depends upon how long the dry weather persists, how severe it becomes and when it occurs during the crop’s development.