Many agronomic practices and standards need periodic evaluation. Soybean population studies are being evaluated across the United States and observing that lower populations do not necessarily result in lower yield. While Delaware results may be similar to those of other regions, our climate and soil types will still have an interaction with plant population.
This study will observe yield results from 5 different planting populations between 60-180,000 seeds per acre in double-crop soybean systems. Double crop populations are typically planted at higher rates than full season beans to make up for the loss of vegetative growth with later plantings. While full-season beans have shown resilience to lower populations under irrigated conditions, we still have to evaluate double-crop planted soybeans for the best recommendations.
Additionally, double crop soybeans typically follow a small grain, similar to full season beans following a cover crop. At this stage, wheat residue has a high C:N and breaks down slowly. How this breakdown interacts with population, row spacing, and canopy closure may provide additional information to those who would like to add residue management to planting decisions.

1) Plant double crop soybeans at five rates between 60-180,000 seeds per acre.
2) Plant double crop soybeans at two row spacings (15 + 30”).
3) Evaluate yield response to planting populations and row spacings.
4) Evaluate wheat residue breakdown under different populations and row spacings.

Soybeans will be planted at the Carvel Research and Education Center in Georgetown, DE into a June harvested wheat field. Soybeans will be planted at five densities (80, 100, 120, 140, 160 thousand seeds per acre) and two row spacings (15 and 30 inch) and irrigated throughout the season. Previous drone flights over the wheat will be compared to biomass and yield data to determine potential interactions by plot and block. Subsamples of wheat fodder will be collected from outside the plot boundaries. Biomass will be separated into decomposition bags for each plot (30 rye and 30 corn fodder), weighed, and placed back into the planted plots in the center of a row. Six subsamples of each will be dried and saved to determine the initial carbon (C), N, and moisture content of the biomass. Six more decomposition bags will be setout side the plots as controls to measure breakdown without soybean canopy. At the end of the season decomposition bags will be collected from the plots, dried, weighed, and analyzed for C, N, and the biomass loss. In three population plots (80, 120, 160), logging sensors will be placed in the 15 and 30” rows to measure EC, moisture, and temperature throughout the season. Yields will be collected
with a plot combine in the late fall.

Data will be analyzed in SAS as a randomized complete block design structured by a factorial including biomass loss, changes in C and N, as well as yield. Yield will also be correlated to various predictors from the study.

Updated July 24, 2024:
Following wheat harvest in June, 2024, soybeans were planted at populations ranging from 60,000 to 180,000 seeds per acre at both 15 and 30" row spacings. Drone flights have been performed for both the wheat growing season and soybean emergence. Deer damage has been more persistent in this field than in the past, but plots are beginning to pull away from the foraging and appear to be in good shape. Irrigation has continued and been performed earlier than normal due to the persistent drought conditions in southern Delaware.