June 21, 2017

Corn Development Phases and their Impact on Potential Yield

The condition of the U.S. corn crop improved slightly last week amid several episodes of showers moving across the Corn Belt. I think the rains helped to stabilize the crop for the time being. They also ushered in cooler temperatures, at least for this week, and there are some additional chances of rain. There were some reports of damage from the strong storms, but I think the rainfall was beneficial overall. The rains did not solve all the dry concerns and additional rainfall will be needed.

Whenever we get toward the end of June, there is always a lot of speculation about what the weather will be like during pollination. The U.S. corn crop this year might reach 50% pollination on July 15-16-17. Pollination is the most important time for corn of course, but several weeks prior to pollination and several weeks after pollination are also very important. The size of the ear is determined prior to pollination and the number of kernels filled successfully is determined after pollination.

Number of rows of kernels - The number of rows around the ear is determined starting when the plant has 5 leaves and it ends when there are about 8 leaves. Therefore, several weeks prior to pollination, the number of rows of kernels has been set. Any significant moisture stress during this period can result in a low number of rows of kernels. The average number of rows is usually about 16. If the conditions are very good, there might be 18 or 20 rows. If the conditions are very bad, there might be 12 or 14 rows.

Number of kernels per row - The length of the ear, or the number of kernels per row, is determined starting when there about 12 leaves and ending at about 15 leaves. This is basically when the plant has reached full height, but prior to pollination. Moisture stress during this period can result in shorter than average ear lengths.

Pollination - The most important period for corn is the approximately 10-day period when the crop is pollinating. The ideal situation during pollinating would be cool and sunny days with plenty of soil moisture. The worst condition would be a combination of hot and dry conditions. If it is too hot and dry, the pollen shedding period may be shorter than normal and the emergence of the silks may be delayed. The pollen shedding period may end before all the silks have emerged resulting in the "nick" being off. The "nick" is the timing between when there is live pollen and receptive silks. A lot of things can go wrong during pollination, so it needs to be closely monitored.

Grain filling - Once the corn has pollinated, the plant still needs adequate moisture to fill all the kernels. If it turns hot and dry after pollination, there may be kernel abortion at the tip of the ear, or what is called tip-back. If the plant runs out of moisture before the filling process is complete, the kernels may be shallow and light weight resulting in lower yields. The ideal situation would be for a slow and long period of grain filling. Those conditions would result in deep and heavy kernels and high yields.

Since we are discussing pollination, one of the concerns this year will be the corn in the eastern Corn Belt that had to be replanted due to spotty stands or being drown out. This very late planted corn probably won't pollinate until August when there is a greater possibility of hot and dry conditions.