Once again, wet soils have delayed corn planting throughout Missouri. The latest USDA/NASS information shows that 27% of intended corn acres have been planted which is half the five-year average. Areas within Missouri differ for frequency of April rains and its impacts on corn planting. Missouri's earliest planted region, Southeast, has experienced the greatest delay in corn planting.
The most important effect from delayed corn planting is a decrease in yield potential. Figure 1 presents data from our study conducted in central Missouri. This is the average of five years and multiple hybrids varying in CRM from 106 to 116. When I sat in college classes well before the turn of the century, agronomists talked about an optimum corn planting date. Our data show that, within the scope of our project, a true optimum does not occur. Instead, a couple of weeks of unchanging high yield is followed by a decrease in yield with delayed planting (our first plating date was during the last week of March). The decrease in yield begins slowly, but accelerates as planting is delayed into late May.
As you might guess, differences occur among years for response of corn yield to planting date. Weather conditions in late June to early August affect corn yield far more than planting date, and weather during those weeks can mask the effect of planting date. In our study, the decrease in yield from April 20 to May 20 varied among years from only 5% to more than 25%. For this reason, it is difficult to predict in any specific year what will happen to corn yield if planting is delayed. But average numbers are our best guide for predicting what will happen in 2022.
If corn planting delays continue, farmers may consider switching intended corn acreage to another crop such as soybean. The costs and benefits of switching corn acreage to soybean vary among farmers and fields. Each farmer must make the decisions for which he/she is comfortable. But our data indicate that switching away from corn may not be appropriate even if planting is delayed until the end of May.
The reasons for decreased corn yield with delayed planting relates to the amount of light captured by plants for photosynthesis, the average temperature during grain filling, and the effects these two parameters have on corn plant development. Corn growth models and data we collected in our planting date studies show that delayed planting delays critical growth stages such as silking and black layer.
The week before and two weeks after silk elongation is the most critical period in determining corn yield as silks emerge from the husk, pollen grains are shed from the tassels, and pollen tubes extend through the entire length of the silk to for fertilization and kernel set. Weather conditions at this time including water availability and heat can greatly affect kernel set success. Delaying corn planting 30 days from late April to late May in central Missouri delays silking about two weeks. Although weather conditions do not vary greatly in July, the potential for dry weather is a little greater for mid-July than early July.
At corn maturity a dark layer forms in the kernel bottom and grain fill stops. Delaying corn planting 30 days from late April to late May in central Missouri delays black layer formation about three weeks from early September to the third week of September. Corn yield is safe from freeze damage at black layer. Fortunately, Missouri farmers seldom have to worry about loss of corn yield from freeze damage even with prolonged delayed planting.
The negative effects on yield from delayed planting are the result of declining number of heat units and the amount of light available to drive development and yield. Available monthly growing degree days (GDD) peaks in July. In August, the available GDD, using normal high and low temperatures, decreases by 6% in August. The decrease is 41% in September. Monthly sunlight totals also decrease during summer months from a maximum in July. Total light energy for August and September is 12% and 29% less than for July. Less light and slower kernel development can decrease corn yield and delay fall harvest.
It is stressful to see idle planters and hear the sound of raindrops hitting the house roof. Although the potential for yield loss exists for Missouri's corn farmer if corn fields cannot be planted soon, our research offer some assurance that profitable yields are possible even if planting is delayed through May. It is difficult to counsel patience as the calendar days pass by quickly, but, if possible, do not plant into soil that is too wet. Compacted soil will result this action and its effects on poor root growth, reduced soil aeration, and decreased water holding capacity may linger long into the growing season and effect yield far more than a few days delay in planting.
Cover image of flooded corn field by Donna Theimer via Shutterstock.