This spring's weather conditions may be slowing down corn planting but soybean planting has not yet been impacted. As of May 5, soybean planting progress is estimated at 8% compared to 11% for the 5-year average (USDA-NASS, 2019). However, because of recent rains and corn planting delays there is concern that soybean planting will soon fall behind. In this article, we discuss the soybean yield potential and maturity selection considerations as planting progresses into late May and possibly June.
First, to put 2019 in context, we analyzed historical USDA-NASS planting date and yield data at the state level. This analysis showed that if 50% soybean planting occurred before May 31 there is a good chance to obtain high yield. In only 3 of the last 40 years, 50% planting completion occurred after May 31. Among these three years, two were extreme years, 2013 was wet early then dry later in the growing season whereas 1993 was wet throughout the growing season.
A question that many farmers have is if they need to switch maturities. There is no need to switch soybean maturity group if planting can occur before June 1 in northern Iowa (Figure 2). In southern Iowa well adapted soybean varieties can be planted into June. Soybean have the ability to adjust development caused by late planting because they are photoperiod sensitive. In recent trials conducted at seven research farms over five years, the same soybean variety planted 40 to 60 days apart reached physiological maturity within 7-10 days of each other. Moreover, a 0.5 to 1.0 maturity group spread resulted in a difference of only 3-5 days to reach maturity.
To compare more planting date and maturity combinations and determine risk of fall frost at more specific regions across Iowa, you can explore the Soybean Planting Decision Making Tool at http://agron.iastate.edu.
While it may be early at this point, if planting is delayed past June 15, the decision must be made either plant soybean using a shorter maturity group than well adapted for the area or consider Delayed and Prevented Planting crop insurance provisions. Planting soybean after May 20 will likely result in lost yield potential of 10% to 50% or more. For delayed and preventative planting the late coverage decreases each day from June 16 to July 10. In prevented planting situations, crop insurance language states the “cause of loss must be insurable and common to the area.”
Bottom line, if planting is delayed past June 15; make a realistic determination of remaining soybean yield potential and feasibility of delayed and preventative planting options. Talk with crop advisors, extension field agronomists and insurance providers to gather information to make the best decision given the situation.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 13, 2019. The information contained within may not be the most current and accurate depending on when it is accessed.