Watch for important yield-determining factors as planted corn moves forward

By Roy A. Ulrich, DEKALB/Asgrow technical agronomist

The long fight with Mother Nature that started in the fall with harvest rolled right into spring and never really relented. As a result, the growing season of 2019 started out by challenging the plans that growers and agronomists had developed over the winter months to produce the highest yields possible while striving for the best return per acre. While most of those plans did not include a mid- to late-May and into June planting dates for corn and soybeans, that is when some growers finally found a dry period to put crops in the ground. Now is the time to reexamine those plans to see which of the yield determining factors could still have a positive influence on the corn crop in 2019.

After all, according to Dr. Bob Nielson from Purdue University only “12 to 16% of the overall yield variability is actually impacted by the delayed planting date.” There is still a very high percentage of the overall yield that we can influence. If you’re interested in how planting date influences overall yield potential, you can find the rest of Nielson’s article at https://www.agry.purdue.edu/ext/corn/news/timeless/PltDateCornYld.html.

The first yield-determining factor in corn that most of you have already assessed is plant population. What kind of plant populations do you have out in your fields and how even and consistently did those stands emerge? The later planting date allowed for warmer soils and the adequate moisture at planting has set up many fields with near perfect stands. So, in many situations this first yield-determining factor is of to a good start with an almost ideal number of plants per acre.

The next yield-determining factor that is currently being set in many corn fields is ear girth. The number of rows around on an ear of corn are set during the V5 to V6 growth stages and has a major impact on final yields. While product genetics have an impact on the average ear girth, environmental factors like weather, nutrient availability, weed competition, etc. can all have an impact on ear girth as well.

By reducing stress from weed competition or lack of nutrient availability, we can maximize overall yield potential. From a weed competition standpoint keeping fields weed free and controlling both broadleaf and grass weeds before they reach 4 inches in height not only minimizes competition for sunlight water and nutrients, it also increases the effectiveness of chemical applications.

Regarding nutrient availability, many growers are in the middle of sidedress applications and with the crop at its current stage it requires almost 75% of its nitrogen still to be up taken into the plant. We are getting ready to enter the growth stage in corn when it requires nearly 8 pounds of nitrogen per acre per day. With such a high percentage of nitrogen needed for crop growth and grain fill still to be taken up by the plant, reducing nitrogen rates just because of a later start could negatively impact overall yield potential.

The next biggest hurdle in determining overall yield potential in corn is successful pollination, which sets up the maximum number of kernels per ear. After pollination you can more accurately assess that maximum yield potential for a field and we can begin to scout to see if any foliar diseases need to be managed to maximize the grain fill.

The late start in 2019 has only slightly influenced the yield potential and there is plenty of growing season left to determine how much corn you put in the bins this fall. One of the ways to reduce the size of that number is to ignore one of these important yield-determining factors.