When does Corn Yield Potential begin to Suffer from Late Planting?

Much like the last three years, frequent rains have delayed corn planting progress in most of the state. I am sure many are already wondering whether you will be able to plant your corn, or whether planting delays may dictate a change of crop intentions. Fortunately, we have a strong research database at Mississippi State University and the University of Arkansas to help answer this question. The primary objective of this research was to evaluate the yield response of modern corn hybrids, possessing Bt technology for corn borer protection, to well later than normal planting dates.  Thus, we can utilize this information to make better cropping decisions, particularly when rainfall delays planting or we are faced with replanting decisions.

Irrigated corn planting date field studies were conducted in 2009, 2010 and 2011 at the MSU Delta Research and Extension Center at Stoneville and the RR Foil Research Center at Mississippi State University using the furrow irrigation method. Corn produced optimal grain yields until about May 1, when productivity began to gradually decline. Corn yield loss was quite moderate through May, until declining quickly in June. The magnitude of irrigated corn yield reduction associated with planting beyond the optimum time frame was 1.3 bu. per day or 0.76% per day for plantings during May and increased to 2.1 bu. per day or 1.59% per day for June plantings. The numbers on the X-axis in the figures below represent the Julian date of the year (75=March 15, 165=June 13). The trendline shows the response of five hybrids (each represented by a different color) planted at 2 to 2 ½ week intervals over the duration of the study.

Dryland studies were conducted at the RR Foil Research Center at Mississippi State University in 2010, 2011 and 2012.  Corn planted at later dates in dryland culture suffered yield loss earlier and more consistent than irrigated corn.  However, pollination failure or catastrophic yield loss never occurred, despite corn being exposed to two of the most severe drought seasons in Mississippi history during 2010 and 2011.  The magnitude of dryland corn yield reduction was 1.3 bu. per day or 0.83% per day for plantings after Mid-April. Although substantial, this productivity loss was relatively moderate and not substantially different from Corn Belt studies. The numbers on the X-axis in the figure below represent the Julian date of the year (95=April 4, 155=June 3). The trendline shows the response of five hybrids (each represented by a different color) planted at 2 to 2 ½ week intervals over the duration of the study.

These results indicate several key findings for Mississippi corn:

1. Foremost, yield reduction associated with late-planted irrigated corn initially gradually decline and escalate over an extended time period. However, irrigated corn productivity does not sharply decline during April or even early May.  Thus, there is little justification to “cut-off”or completely abandon corn planting intentions, if planting is slightly delayed past optimum dates.
2. Also, these results show irrigated corn may produce optimum yields about 10 days later than our old guidelines, which differ depending upon latitude regions of our state.
3. Yield reduction associated with late corn plantings grown in dryland culture is likely to steadily decline and is a more significant limiting factor, compared to irrigated corn.
4. Based upon our research, this figure represents more appropriate corn planting guidelines for Mississippi.