Soybeans are a globally significant commodity, providing a major source of protein and oil for both human and animal consumption. The scale of this crop requires a standardized system for trade and cultivation, often involving converting bulk measurements, like the bushel, into precise individual units. Understanding the number of seeds contained within this bulk measure is fundamental for agricultural planning and economic calculations, driving planting decisions across millions of acres.
The Standard Bushel and Average Seed Count
A bushel is the standard unit of trade for soybeans in the United States, defined by the U.S. Department of Agriculture as a net weight of 60 pounds of seed. This weight-based standard is used because soybeans are a variable product, and a volume-based bushel would fluctuate too much based on density and moisture content. The number of seeds within this 60-pound measure is highly variable, typically ranging from 132,000 to 240,000 seeds.
The accepted average often falls around 140,000 to 150,000 seeds per bushel, equating to approximately 2,333 to 2,500 seeds per pound. Farmers rely on specific lab tests for the exact count of the seed they purchase, as this average is merely a midpoint. Seed companies frequently sell soybeans in “units” that contain a guaranteed number of seeds, often 140,000, based on this typical bushel average.
Factors Driving Seed Count Variability
Seed Size and Density
The density of the seed, or how many individual seeds it takes to accumulate one pound of weight, is the most direct cause of count variability in a bushel. Smaller seed size means more individual seeds are required to meet the 60-pound weight, increasing the overall seed count. Conversely, ideal growing conditions often produce larger, heavier seeds, resulting in a lower seed count per bushel. This individual seed size is typically measured and reported as the number of seeds per pound.
Genetic and Environmental Factors
Genetic variety plays a role in size determination, as different soybean cultivars are predisposed to produce seeds of varying weights and densities. Beyond genetics, the growing environment significantly influences the final seed size. The availability of moisture during the seed-fill period late in the season is particularly important. A drought during this phase can shorten the seed-fill window, leading to smaller, lighter seeds and a higher seed count per bushel.
Moisture Content
Moisture content at harvest also influences the effective seed count for a 60-pound bushel because water adds weight without adding seeds. While the official standard for soybean trade assumes a certain moisture percentage, variation in the moisture level affects the actual quantity of dry matter and the true number of seeds contained within the standardized weight.
Practical Use in Planting Rate Calculations
Knowing the exact number of seeds per pound is foundational for calculating the optimal planting rate. Modern agriculture focuses on planting a specific count of seeds per acre rather than a certain weight. This shift allows for the precise management of the target plant population (TPA) needed to maximize yield potential.
Calculating Seeding Requirements
To begin the calculation, a farmer determines the final target plant population (TPA), which is the desired number of established plants per acre after accounting for losses. Using the seeds-per-pound measurement from the seed lot, the farmer calculates the required weight of seed to purchase. This calculation must also incorporate the expected field emergence rate, as not every seed planted will successfully grow into a mature plant; typical emergence rates are often estimated around 80%.
Field Implementation
This precision extends to the field, where the seeding rate is converted into the necessary number of seeds per foot of row, based on the planter’s row spacing. Utilizing the seeds-per-pound figure allows the planter to be calibrated to dispense the correct weight of seed to hit the target count. Careful management of the seeding rate is important for economic planning, as soybean seed is a significant input cost, and improper planting can directly reduce profitability and final yield.