June 28, 2012

Next Two Weeks Critical for U.S. Corn Crop

The next two weeks will be critical for the U.S. corn crop because that is when much of the corn will be through pre-pollination and into pollination. Elevated temperatures in the central and eastern Corn Belt will be particularly important in the areas where moisture shortages are already severe.

Pre-pollination is when the size of the ear is determined and moisture stress during that period can result in smaller than normal size ears. Under severe stress, instead of the normal 16 rows of kernels per ear, there may only be 14 rows or 12 rows of kernels. Even though there may be the normal number of kernels per row on the ear, continued moisture and heat stress during pollination can result in not all the potential kernels being pollinated. Even after pollination, if the plant continues to be severely stressed, kernels that were pollinated can start to be aborted. That leads to what is called tip-back, or the last few inches of the ear being devoid of kernels.

Continued stress can also lead to a shortened period of grain filling resulting in small kernels that are lighter than normal and lower yielding. If the stress is severe enough, the plant starts to cannibalize the lower leaves in an attempt to keep the upper leaves of the canopy supplied with enough water and nutrients to conduct photosynthesis. If the upper leaves of the canopy are not able to fully utilize the available sunlight, then the kernels can end up weighing less than normal resulting in lower yields.

Even though it is not yet a critical time for the soybean crop, the month of June has been a poor month for much of the soybeans in the eastern Corn Belt. The hot and dry conditions have resulted in very slow growth or no growth at all. The result has been that a significant portion of the crop has lost several weeks of potential growth, which puts the crop at risk of being shorter than normal and lowers yielding than normal.

Soybeans have an amazing ability to recuperate from adverse conditions early in the growing season by setting new flowers and pods later in the summer if conditions improve. The concern for the U.S. soybean crop is that the hoped for improved conditions need to materialize before the middle of July in order to allow enough time for additional growth. In the meantime, for every week of moisture stress, the soybean plant misses an opportunity to put on additional flowers and pods.

The most important time for the soybean crop is during pod filling, which usually occurs during the first three weeks of August. If the plant is undergoing moisture stress during pod filling, then instead of the normal three seeds per pod, there may be only two or none at all. Additionally, the seeds are usually smaller than normal if the plant is under moisture stress. All of this can contribute to disappointing yields.