Published: May 06, 2009 07:39 am      

Corn planting date effect on yields

Wet weather since late March has delayed corn planting. According to the National Agricultural Statistics Service, only 20 percent of intended corn acreage was planted in Kentucky as of April 26 compared to the five-year average of 57 percent. If recent weather forecasts hold true, corn planting will continue to be hindered through early May.

So, when can we expect to lose yield on corn based on planting date? Research indicates that corn should be planted by early- to mid-May to avoid yield losses. In west Kentucky, corn should be planted by May 1-5, according to six years of research at that the UKREC in Princeton, Ky. Extrapolating these results to other areas of the state: corn planting should be completed by May 1 in extreme western Kentucky; by May 5-10 in west-central Kentucky; and by May 10-15 in eastern Kentucky to achieve maximum yield potential. There is an average yield loss of 1 to 2 percent per day for corn planted after early May (west Kentucky) to mid-May (eastern Kentucky).

Most of you reading this and looking at weather forecasts know that you will not get all of your corn in the ground before these dates. Don’t panic. There is more to this story.

While our research indicates yields losses for corn planted sometime after the first or second week of May, statewide average yields tell a slightly different story. If at least 80 percent of the corn crop is planted by the third week of May, then we still have a chance for good yields. Actual planting date and yield data from a central Kentucky farming operation would imply that the optimum window for planting is around the first or second week of May.

Some of the other factors that affect corn yield include timely rainfall, adequate heat units, low stress at pollination, adequate nutrients, etc. So, if the rest of 2009 turns out to have favorable weather, we would expect any potential yields losses from late planting to be much less than predicted.

Some things to consider when planting corn in May:

• Use a corn hybrid with the Bt trait for corn borer. University of Kentucky research shows a yield benefit and an economic benefit to Bt corn borer hybrids planted in May. The later the planting date, the greater the yield benefit for the Bt hybrid.

• Possibly switch to an earlier-maturing hybrid. Based on calculations of growing degree days remaining in an average season, hybrids with relative maturities of 118-day (and less) will reach physiological maturity (black layer) before frost in west Kentucky even if planting is delayed until late May. For late May plantings in central and eastern Kentucky, hybrids of 116-day relative maturity or less are likely needed. If planting occurs in early to mid-June, then a switch to hybrids of 113 to 116-day relative maturities likely will be needed. For extremely late plantings (after mid-June), hybrids of 110 to 113-day relative maturities or less are needed.

• Keep the seeding rates and row spacing the same. Two exceptions: if someone convinced you to try 38,000 seeds per acre, try it in a small area instead of a large field. Your odds of getting decent yields from late plantings are good, but your odds of getting excellent yields are not.

Source: Jim Herbek and Chad Lee, Extension Agronomists, Plant and Soil Sciences, University of Kentucky

Educational programs of the Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin.