Current Impact of Dry Weather on Corn Yield

Hot and dry with an opportunity for rain on the weekend. That has been the forecast for several weeks yet we have missed timely rains. Corn is rolling and wilting in parts of area fields or complete fields.
In many corn fields, we had good stands until we lost plants through rootless corn syndrome. Plants that failed to establish themselves wilted and died. Other plants which were planted early season also had side-wall compaction and grew slowly. In past springs, it was wet and we pushed to ensure we had crops planted timely.
Corn is yellow in some fields exhibiting nitrogen deficiency. The corn roots have not grown into the ammonia band or dry soils have limited nitrogen uptake.
So what is the impact of dry weather on corn yields up to now? Corn yields are dependent on population, number of kernels per plant and the weight of each kernel. All of these are decided as the season progresses. We have passed the population. Next, is the critical stage of the number of kernels per plant.
Corn has passed the V-7 leaf collar stage and the number of rows per ear has been determined by the plant. This is primarily determined by genetics.
Next is the potential number of kernels per row which is greatly influenced by dry weather. The potential kernels per row are determined by V-15 or 15 leaf collar stage. Dry weather during this stage can reduce the number of potential kernels per row causing a significant impact on yield. Later, during pollination, the number of kernels pollinated will form kernels. Additional stress can cause kernels to abort.
Drought stressed plants early season also result in small plants. Small plants do not have the size to capture sunlight compared to large plants. Therefore, small plants have a reduced ability to provide energy to kernels. As we move forward, timely rains could provide us moderate yields. Continued dry weather will reduce corn yields.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.