By Maninder Singh
Soybean extension agronomists from across the U.S. worked together in 2020 to summarize research related to planting date, seeding rate and row spacing. This effort was funded by the United Soybean Board. Data contributed from Michigan was generated based on research funded by the Michigan Soybean Committee. Below is a short summary of what we found. To access full reports on each of these topics, please visit our website: MSU Cropping Systems of Agronomy - Soybean.
Timely planting of soybean is critical in achieving high soybean yields. In many instances, this means planting soybean as early as field conditions allow, but generally at or after the Risk Management Agency (RMA) replant crop insurance dates begin. In Michigan, we estimate a yield reduction of 7% when planting soybean on May 31 compared to May 1, with majority of decline occurring after mid-May.
Timely planting allows for soybean to maximize light interception and canopy photosynthesis, increase number of nodes and seeds per unit area, and lengthen the seed filling period. However, careful planning is required to minimize risks associated with early planting.
Soybean plants are very flexible at adjusting to a wide range of plant populations. Soybeans branch out and can produce high yields even at relatively low plant densities. For normal planting dates in Michigan and across the Midwest, generally 100,000 to 120,00 plants per acre is enough to achieve maximum yield. A higher population density is needed as soybean planting is delayed into mid-June. Recommended seeding rates vary considerably but are often around 25% higher than the target plant population.
Soybean row spacing used by growers varies widely across the U.S. In Michigan, most farmers plant soybean in 15- or 30-inch row widths. Across the U.S., narrow rows (less than or equal to 15 inches) out-yielded wide rows (greater than or equal to 30 inches) 69% of the time. This is probably due to earlier canopy closure in narrow rows that enables more light interception and drives photosynthesis.
Source : msu.edu