RALEIGH, N.C. — Using the optimal soybean planting date is critical to maximize yield for our full season soybeans. Earlier planting dates typically result in more main stem nodes; more nodes result in more flowers and pods and subsequently higher yields. This national publication on soybean planting dates thoroughly explains the benefits of earlier soybean planting. There is much energy across the United States on planting soybeans earlier than historical for the associated yield benefits. In a recent analysis of 877 North Carolina Soybean Yield Contest entries, one of the strongest predictors of high soybean yield was the use of planting dates earlier than mid-May.
What is the optimal soybean planting date in North Carolina?
The optimal planting period in North Carolina was historically defined as May 1 to June 10, however as we shift to using earlier maturing varieties and more aggressive management strategies we need to redefine the optimal planting period. It will take several years of research to do this. The Soybean Extension Program started this research in 2019 investigating the impact of soybean planting date on soybean yield and quality and will continue to do so for several years. We have data from 2019 and 2020 from 8 North Carolina locations that include in 2019 Currituck Co., Hyde Co., Sampson Co., Union Co., and Yadkin Co. and in 2020 Beaufort Co., Robeson Co., and Rowan Co. We had variable response to planting date across years/yield environments, so we broke this data into high (Beaufort Co. 2020, Currituck Co. 2019, Rowan Co. 2020) and lower (Robeson Co. 2020, Sampson Co. 2019, Union Co. 2019, Yadkin Co. 2019) yield environments.
In the higher yield environments, soybean yield was highest at the earliest planting dates (mid-April) for maturity group ≤5 and declined as planting date was delayed (Figure 1). For the lower yield environments, yield was highest for soybeans planted from late April to mid-May regardless of maturity group (Figure 1). There was some yield penalty for late March to mid-April planting dates in the lower yield environments (Figure 1), which is likely driven primarily by the hot, dry May/early June in 2019. Regardless of high or low yield environments, there were benefits of planting soybeans by mid-May. Over the past five years, soybean acres planted behind wheat have comprised 15-35% of our overall soybean acres, however, our planting progress by the end of May has only been 50-60% of our soybean acres (USDA-NASS). This means a lot of full-season soybeans could benefit from earlier planting dates. Rotational complexity does play into decision making about soybean planting date, but soybeans are less sensitive to most of our row crops planted into cool conditions and for this reason, growers may consider planting soybeans earlier than some of the other crops in their rotation for the associated yield benefits. We had drastically different conditions in May 2019 (hot and dry) and May 2020 (cool and wet) which inevitably influence the impact of planting date on soybean yield across the two years and underscores the importance of doing this research over multiple years before redefining the optimal planting period for soybeans in this state.
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–Rachel Vann, N.C. State University