Soybeans will be planted for a third year at the Carvel Research and Education Center in Georgetown, DE on three different dates. This includes mid-April, early May, and late May. The same variety (mid group IV) will be planted on all three dates. Following emergence, plots will be assessed for early season seedling diseases and will be scouted for disease throughout the season. Tissue and soil samples from each plot will be sampled at R1-R2 to observe any differences in nutrient uptake. Yield will be collected at the end of the growing season using a plot combine. Tissue and soil samples will be analyzed by the University of Delaware Soil Testing Lab. Tissue nutrient content will be correlated to yield, soil nutrient levels, and soil type. Trends in yield related to planting date, nutrient content, and soil nutrient status will be compared.

Additionally, this project is also being submitted to the MD Soybean board by the University of Maryland to add additional sites across the Mid-Atlantic. This will allow for the robust examination of climate and soil type of soybean planting dates.

Updated March 19, 2023:

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Untreated group IV soybean seeds were planted at the Carvel Research and Education Center on April 13th, 26th, and May 11th. Despite freeze damage to the April 13th planting, yields, yields were similar across all treatments, ranging from 67 to 68 bushels per acre.

Tissue and soil samples were taken at the R2 growth stage, and almost all nutrients had some differences based on planting timing. However, all nutrients were within within sufficiency ranges, despite having different concentrations based on planting timing. Although each treatment was planted two weeks apart, tissue sampling occurred within one week. This is because most studies reached R1/R2 at similar Julian dates, since the 1st planting would have slower early growth with cooler weather.

Only Ca was borderline deficient in the tissue and was also lowest for the May 11th planting date. While S was not deficient, it was on the lower end of sufficiency ranges. Sulfur dropped in the soil with later planting but was higher in the tissue. Since most soil samples were taken at similar time points, this may represent plant uptake more than leaching from the profile. The nutrients P, K, Mg, Zn, and Fe were all higher with earlier planting dates, but B (like Ca and S) was highest in the tissue from the last planting date.

Like the 2020 and 2021 study of planting timings, Al concentrations were lower in the tissue with later plantings, with a pH relationship only occurring during the earliest planting. The uptake of Al within soybeans can be variety or pH related, but in all three years has certainly been planting date related.

So, while planting date can influence tissue concentrations of nutrients, it may only matter when fertility is lacking, or an antagonistic relationship occurs. This could include drought conditions, which were not evaluated in this study. Currently, we would not recommend any variation in soil fertility based on planting date, but antagonistic relationships with Al uptake should be studied.