With a shift towards some more rainy conditions, and many of you recalling our planting timeline from 2019, we’ve had an increase in calls and questions on the yield potential of May planted corn and soybeans. We hope to answer some of those questions in this blog post.
1. Research out of several Midwestern states has shown there is not a direct correlation between early planting date and corn yields. A study from UNL looked at planting date and yield over the past 25 years and discovered that while there isn’t a direct correlation of early planting and higher yields, there is a window from Mid April to Mid May where yields are more consistent, and to try and fit the bulk of our corn planting in that window. Outside of that range, much more yield volatility is likely. We also need to remember that expected yield is relative to the growing season. An article out of Purdue points this out. Early planting followed by poor conditions during the growing season can result in much lower yields than late planting followed by an ideal growing season. In fact, their data suggests that 12-16% of the variability they see in yields is from planting date. That is likely much lower than the impact we perceive it has in our planning. We see this in years like last year, with some late May, even early June planted fields that still yielded phenomenally, much better than some of our 2018 yields. Planting date isn’t everything. In fact, its only one fairly small thing. Research from both of these universities suggest that pushing planting dates earlier is not a priority and does not have a large impact on final yield. (Up to a point around late May, generally speaking.)
2. Soil conditions are a much larger influence than planting date. Planting into soil conditions with adequate temperatures, and without drastic changes in temperatures for 48 hours will maintain seed viability and help with uniform emergence. The same goes for moisture. Planting into a good seedbed with appropriate soil moisture will largely influence of our initial stand, as well as help promote uniform emergence of seedlings. We've discussed the importance of uniform emergence in several posts, and you can see our results from the last couple years here. Mudding a crop in because the calendar says to will never serve us well. Anecdotally, we usually see that our soil conditions are a much larger influence on yield until late in May. Only then does the planting date start having a larger impact.
3. There is a much more definite trend for planting date and soybean yields. A general rule is that for every day past May 1 planting is delayed, we can expect a 0.25-0.625 bu/ac yield reduction. This rate is generally toward the lower end of that range at the beginning of May and towards the higher end of that range as we get into June. To better hit this window, we’ve seen a trend the last several years with operations planting some beans first, switching and planting all of the corn crop, and finishing up beans after. This does help insure some of the acres get in before we start seeing a potential yield reduction. Keep in mind, just like with corn, the yield we expect from soybeans will be relative to the growing season. Early planting will not guarantee more yield. It does however seem to show a stronger relationship between planting date and yield with soybeans than with corn.
So, what’s the bottom line? In regards to corn, early planting date doesn’t ensure higher yields. Early and Mid May plantings still have the potential for high yields. Soil conditions at planting are much more important. Planting of beans past May 1 will start to see some yield decrease of about .25 bushels/acre per day. With both crops, this yield potential is relative. Late planting will have minimal impact if we have an ideal growing season. With that in mind, let’s do the best job we can to get our crops planted in ideal soil conditions and get them off to a great start.
I’d encourage you to read these great articles for UNL and Purdue for more details on how they used 25 years of yield data to look at planting date trends.