Another CropWatch article this week addresses the question “How does planting date impact corn yield in Nebraska?” Our general conclusion was that there is a “planting window” within which yields are often very similar and after which yields decline rapidly. That window seems to begin closing after mid-May.

Last year in a CropWatch article several of us discussed the concept of corn planting windows, citing data from studies at Iowa State University (Elmore et al., 2018). The 2018 CropWatch report was based on the journal article by Abendroth, et al. 2017. In the CW summary of that article, we stated, "… rather than thinking of a specific date as optimum for planting—with certain declining yields certain to follow—we need to consider buffer periods around optimum planting dates as a window of time within which corn yields are optimized."

How consistent is the concept of a window for optimum planting across the rest of the Corn Belt? To answer that question, we’ll review published research from the central Corn Belt.

Nafziger, University of Illinois, planted corn at six Illinois locations for three years with four planting dates ranging from early April through early June. Yield losses were less than 1 bushel per acre per day until at least 20 days after the optimum planting date. With optimum planting dates of April 11-20 for his central and northern Illinois locations, potential yields by May 10 were within 4%-5% of the optimum yield. Southern Illinois yields were more affected by later planting. The central and northern locations are more similar to Nebraska’s conditions. Highest yields came from both their earliest planting date as well as from the mid-May planting date.

Nielsen, Purdue University, recently updated an article on corn planting dates. He compared Indiana planting progress dates to trend-line yields using USDA-NASS data. (We modeled this approach in our companion CW story.) There did appear to be some relationship, but planting date accounted for only 12%-16% of the variation in trend-line yields. He concluded that a number of other factors collectively influence planting date responses in any given year. In addition, he—similar to Nafziger—noted that early-planted corn may yield more, less, or the same as that of a later planting date in another year since so many other factors influence yield. A good share of the variability in yields depends on what happens after planting.

Long et al., Kansas State University, 2017 compared planting dates and yields from the National Corn Growers corn yield contest winners (2011 to 2016) to those from three decades of published research. They looked at the data in two ways.

For the contest winners, planting date was more important in high latitudes―above 40⁰ N―than more southern locations. Not only were the ranges of planting dates earlier in southern latitudes, but also a wider window existed in the south within which yields remained constant.

The most frequent planting date range for contest winners in our latitude―between 40⁰ and 45⁰ N latitude―was between April 29 and May 15. Most of Nebraska’s contest winners planted between April 24 and May 15. (See Figure 2 of Long et al, 2017.)

For the contest winners, 92% of the yield variation was accounted for by the interaction of ”…different factors [not including planting date] and the error term.” Year and location accounted for 6% of the variation. Planting date accounted for only 1% of the yield variation. Interestingly, differences among winner’s yields were influenced neither by tillage, fertilizer, nor seeding rate.

Long et al. separated the contest winner yields into three categories:

• “Medium Yield,” 80 to 160 bushels per acre;
• “High Yield,” 160 to 240 bushels per acre; and
• “Very High Yield,” more than 240 bushels per acre.

Contest winner yields in our latitude zone classified as High Yield were 6 bushels per acre higher when planting occurred before May 15 than after May 15, but later planting dates were not frequent for this yield group. Surprisingly, planting date did not affect yields of contest winners with either “Medium” or “Very High” yields. This would suggest that factors other than planting date were limiting.

Contest Winners versus Published Research: When the contest winner data were compared to that of the published research, they found that the northern latitudes―including Nebraska―had a “tighter” planting window than more southern latitudes for both data sets. Long et al. summarized their work by saying that “…as the maximum attainable yield increases, the effect of planting date as a main critical factor becomes less relevant.”

Baum et al. 2019 investigated the effect of planting date on several hybrids at seven Iowa locations over three years. Hybrids planted in their northern locations ranged from 95 to 109 relative maturity (RM) while those in the south ranged from 106 to 113 RM. The four planting dates at each site ranged between mid-April and late-June. Based on their analysis of variance with only planting date and hybrid maturity as variables, they attributed 70% of the variation in grain yield to planting date and 10% to hybrid. Combining their data with that from other Corn Belt studies, they found the optimum planting window ranged from April 22 to May 10 (Figure 1). They defined the optimum window to be that in which 95% or greater yield potential is attained (personal communication, M. A. Licht, April 2019). The optimum planting date was around May 5.

In their study, Baum et al. also found that planting later resulted in significant delays in silking as well as maturity; yields decreased dramatically with silking after July 23. Silking after that date resulted in a 0.75% yield loss per day because of a shortened and less favorable grain-fill stage. They also found that their northern locations had narrower optimum planting windows. Planting full-season hybrids mid-April through mid-May resulted in higher yields than shorter RM hybrids; however, with planting dates after mid-May, RM choice did not affect yields significantly.

Summary and Last Thoughts

How consistent is the concept of a window for optimum planting across the rest of the Corn Belt? This summary of Corn Belt data and the data presented from Nebraska in the companion CW article point to a similar conclusion: There’s a planting window between mid- to late-April and mid-May within which optimum yields are usually obtained. After this period, yields decrease rapidly.

References

Abendroth, Lori, J, Krishna P. Woli, Anthony J.W. Myers, and Roger W. Elmore. 2017. Yield-Based Corn Planting Date Recommendation Windows for Iowa. Crop Forage and Turfgrass Management. Volume 3. doi:10.2134/cftm2017.02.0015.

Baum, M.E., S.V. Archontoulis, and M.A. Licht. 2019. Planting Date, Hybrid Maturity, and Weather Effects on Maize Yield and Crop Stage. Agronomy Journal, 111: 303-313.

Elmore, R., J. Specht, J. Rees, H. Yang, and P. Grassini. 2018. Cold soil temperature and corn planting windows. University of Nebraska, Extension CropWatch, April 12, 2018.

Long, N.V., Y. Assefa, R. Schwalbert and I.A. Ciampitti. 2017. Maize Yield and Planting Date Relationship: A Synthesis-Analysis for US High-Yielding Contest-Winner and Field Research Data. Frontiers in Plant Science. 8:2106. doi: 10.3389/fpls.2017.02106

Nafziger, Emerson. 2008. Thinking About Corn Planting Date and Population. The Bulletin (No. 2, Article 7, April 4), University of Illinois Extension.

Nielsen, R.L. 2019. The planting date conundrum for corn. Purdue University. Agronomy.