Research Update: Soybean Planting Date and Maturity Group Impact on NC Soybean Yield

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Soybean planting date and maturity group (MG) are important management considerations for soybean production in North Carolina. A recent analysis of 877 North Carolina soybean yield contest entries from 2002-2019 indicated that planting before mid-May and using maturity groups ≤4 increases yield in high yielding situations. Further investigation into the impact of these management strategies on yield across more diverse production environments is important, as most of our fields in this state encounter more stress than would an entry into the NC Soybean Yield Contest. 

The NC Soybean Extension program has been investigating the impact of planting date and maturity group on soybean emergence, flowering, yield, seed damage, purple seed stain, protein, and oil for the past 3 years (2019-2021). In each environment, we have evaluated maturity groups 2-7 at planting dates from mid-March through mid-July. More details about the methods used in this study can be obtained in this scientific publication

This research will continue in 2022 and 2023 with the ultimate goal of creating a grower decision support tool that will allow growers to enter their planting date and the tool will generate a prediction on the best maturity group and seeding rate combination to use at that planting date. We would like to have enough data so that growers could filter in the tool by things like yield environment, location, soil type, and latitude. In order to create a tool that is robust, data must be captured that represents different weather patterns, geographical locations in NC, soil types, and latitudes. 

Our current dataset has 11 environments across North Carolina from 2019-2021 (Table 1). Working with a statistician and scouting the trends across individual environments, we have pooled the data into high and low yield environments (Figure 1). High yield environments have a site average >60 bu/A.

Planting Date: In high yield environments, yields were typically highest with early to mid May planting for most maturity groups (Figure 1). Yields were slightly lower both when planting before May and in late May compared to planting in early to mid May. Yield declined considerably when planting dates were pushed past May across all maturity groups (Figure 1). 

In low yield environments, yields were highest for MG3-5 when planted in mid to late May and yields were similar with late April to late May planting for MG6-7 (Figure 1). Considerable yield declines were observed when planting before mid-April and after mid-June at these environments (Figure 1). Yield declines from planting before mid-April at these environments are not well understood but may be attributed to soil type interactions with cooler weather limiting vegetative growth prior to soybeans moving into reproductive development and seed damage encountered at earlier planting dates. Yield declines at planting dates past May are expected and well documented in the literature. 

Maturity group: Planting date and maturity group interact to affect soybean yield, meaning that the same MG is not the best across all planting dates. In high yield environments, MG4 and MG5 yielded highest when planted before May (Figure 1). In lower yield environments, MG6 yielded the highest when planted before May (Figure 1). At full season planting dates in May, MG5 and MG6 tended to provide the highest yields regardless of yield environment (Figure 1). At planting dates past May, our data so far indicates that growers have flexibility in using MG4-7 regardless of yield environment (Figure 1). 

This research continues in an effort to understand the impact of environment characteristics (weather, soil type, latitude, yield environment) on soybean yield so that robust recommendations can be made about maturity group use across planting dates.

Table 1. Yield environment, county, year, and mean yield for the 11 environments across NC where this research was conducted from 2019-2021.

Figure 1. The impact of planting date and maturity group on soybean yield in high (n=5, blue) and low (n=6, red) yield environments across North Carolina from 2019-2021.