Soybean Planting Research Updates

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Planting Date Decisions
Over three seasons (2020-2022) the Delaware Soybean Board supported research observing different planting dates for soybeans, which ranged from April 12^th to June 4^th, depending on the year. All three studies were done at our research farm in Georgetown, DE where we observed no differences in yield for a maturity group 4.5 soybean.

Seeds were left untreated so that any early season diseases could cause losses, but none were observed during the study, besides some diaporthe. In 2021, stands were reduced on the earliest planting due to an issue with a row unit planting too deeply, yet yields remained similar at the end of the season. We also observed some freeze damage in 2022 on the earliest planted beans, but no yield differences by the end of the season. One interesting note was that soybeans typically had less aluminum in their tissue with later plantings, and this could be related to yield losses, and could be diluted with higher soil pH. More work needs to be done to understand the mechanism of aluminum availability in the soil.

We did not observe a yield boost with earlier planting, as some states have reported. But, we also did not observe yield losses, despite a lack of seed treatment, planting depth mistakes, and freeze damage. Results will certainly vary across the state, based on local weather conditions and pathogen vectors, but mid-April planting of soybeans may be a safe bet for southern Delaware.

Table 1. Soybean yields based on planting dates from 2020-2022.

Figure 1. Freeze damage to soybeans planted on April 13, 2022, did not result in any yield differences by the end of the season.

Row Spacing and Population Decisions
As noted in an earlier Delaware Agronomy Blog post (https://sites.udel.edu/agronomy/2023/01/27/2022-soybean-yield-response-to-planting-populations-row-spacing-and-irrigation-in-delaware/), we have not observed yield differences in full season beans planted between 60-180,000 seeds per acre. We did observe a yield boost of 10.6 bushels when planted in 15” rows over 30”, as well as 25.9 bushels in irrigated plots.

Populations can certainly be lowered to what you are comfortable with, as long as considerations for reduced stands due to disease, pests, and soil conditions are also considered. Lower populations will also take longer to canopy, particularly in 30 inch rows, which may allow for greater weed pressure.

Rainfed plots senescing earlier under our variable rate linear irrigation field.