Effect of Late Planting Dates on Corn Yield Effect of Late Planting Dates on Corn Yield

Planting date studies have been conducted for corn over many years. Often the focus has been to determine optimum planting date for maximizing yield. In some areas, planting early-maturing corn hybrids as early as possible has been a successful strategy for avoiding hot, dry conditions at the critical pollination and early grain fill stages. Planting later can be an alternative strategy that attempts to avoid the most intense heat by moving the critical growth stages for corn centered around pollination to later in the growing season. This strategy has been adopted by some growers in areas that often encounter heat and moisture stress during the growing season. However, crop insurance cutoff dates for planting are earlier than some farmers may want to plant some of their corn acres. The purpose of these studies was to assess the yield potential for corn planted after the insurance planting cutoff date and to compare corn yields from a wide range of planting dates. Corn planted from the second week of June until even the 4th week can yield from 50 to 70% of the highest yield of the earlier planting dates.

to 40-ft long. Yields were determined from the middle two rows of each plot to avoid influence from neighboring plots. Usually, two harvest dates were required at each location to allow the later planted corn to mature and dry sufficiently for harvest. Yields were corrected to 15.5% grain moisture. Nitrogen and weed control were managed to have no effect on yields.

Results
In 2018, the growing season started off cool, with seedlings from the first planting date taking more than 16 days to emerge, but the weather warmed up quickly. Seedlings from the second planting date emerged approximately 3 days after the first planting date emerged. The rest of the growing season continued to be warmer than average, with below-average rainfall during April through July. Although temperatures remained high in August, rainfall exceeded the 30-year average.
In 2019, there was a cool period in early May, then temperatures were closer to average for June and July, with August being cooler. Rainfall was above average for every month except July, with some months more than double the 30-year average. At Topeka, the corn emerged 10, 6, 4, and 5 days after planting for the respective planting dates.
In 2020, there were cool periods in April and May that slowed the emergence of corn planted earlier, however, June was warmer and drier than normal, requiring irrigation at Topeka. July was wetter than normal with 3 times the average rainfall. Corn emergence was 19, 12, 7, and 5 days for the earliest to latest planting dates, respectively.
In 2021, similar to 2020, there were cool/cold periods in April and May, with snow on April 20, that slowed corn emergence in the earlier planted corn. The days to emergence at Topeka were 20, 14, 7, and 4 days, respectively, for the earliest to the latest planting dates. At Ottawa, the day to emergence were 35, 14, 7, and 8 days for earliest to latest planting dates, respectively.
The 2018 and 2019 yield results from Ottawa were greatly influenced by the weather, specifically hot and dry periods in July when the corn planted in early to mid-May was trying to pollinate. As a result, the corn planted at the end of May or first week of June yielded as well or better than the earlier planting dates because rain events occurred when the corn was pollinating (Tables 1, 2). Corn planted in the last week of June had good pollination weather but yielded 60-70% of the highest yields each year, reflecting the lack of growing season that reduced yield potential.
The corn yield response to planting date in Ottawa in 2020 was very different than the previous two years, with the highest yield 40 to 80 bu/a higher than the two previous years. The above-average rainfall in July was favorable for pollination, resulting in the highest yields from corn planted at the end of April through mid-May for both the short and full season hybrids (Table 3). Corn planted in the first week of June yielded just greater than 70% of the highest yields. The full season hybrid yielded more than the short season at every planting date, indicating that switching to a shorter season hybrid due to delayed planting will not increase yield.
In 2021, the highest corn yield at Ottawa was with the early April planting of the full season hybrid, similar to 2020 (Table 4). The next highest yield was with the short season hybrid planted the first part of June, very different from the previous years. In contrast, the lowest yield was with the short season hybrid planted in early April. The June 23 planting experienced hot/dry conditions shortly after planting, resulting in crusting issues with very few plants emerging (data not shown), therefore, the data from that planting date were not included in the results.
For all years at Topeka, the yield-limiting factor of moisture stress was greatly reduced by repeated irrigations, resulting in a more traditional yield response to planting date (Tables 5-8). The highest yield was when corn was planted in the last half of April in 2018 and 2019 (Tables 5, 6). In 2020, the highest yield was with the April 10 planting date for both the short and full season hybrids (Table 7). The full and shorter season hybrids' yields were almost equal when planted June 11. Similar to 2020, the highest yield in 2021 at Topeka, was with the full season hybrid planted in early April ( Table  8). The short season hybrid planted early had the lowest yield, similar to results from Ottawa this year. Both hybrids planted in early June averaged 70% of high yield for the study.
Generally, grain test weights were lower with the last planting dates at both locations for all years, especially with the full season hybrid (Tables 1-8). This reduction in grain test weight was related to the shorter grain fill period for the later planting dates.
Overall, the planting date for the highest yield at Ottawa varies, depending on the environment experienced that year (Figure 1). With irrigation to help reduce some of the variability at Topeka, the highest yield tended to be with the earlier planting dates (Figure 2). Planting corn in June at Ottawa generally yielded 70% of the highest yield, and the June planting at Topeka generally averaged 60%.
Switching from a full to a shorter season hybrid due to delayed planting generally did not increase yield at either location. However, the shorter season hybrid may not take as long to mature and dry down at harvest (Tables 1-8).
The preliminary results from four years of experiments provide an example of how later planting date can be a viable option to avoid stressing the corn at critical stages when moisture is limiting, or when planting is delayed because of excess rainfall. The results from the irrigated experiment at Topeka illustrate that if moisture is not limiting, but planting is delayed, corn can still produce a substantial yield, though reduced from the potential of the optimum. These data also show the variable response to planting date in dryland production of corn in Kansas, which is often related to the conditions at pollination.

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