Does seed size make a difference when deciding on what plant population to seed? A pound of soybean seed can range from a low of 2,000 seeds to a high of 3,200 seeds, but generally falls in the range of 2,400 to 2,800 seeds per lb.
This makes a difference when bagging seed, since a unit of seed (140,000 seeds) will weigh differently when seeds are small and light versus fat and heavy. Several Illinois growers have asked whether, if they have large soybean seed at planting, they can reduce their planting population due to higher percent emergence.
In regard specifically to seed size, larger seed generally has larger energy reserves and a more sustained supply of energy. You could conclude that in challenging environments it would have a better opportunity to survive and germinate in cool and wet springs as long as it is adequately protected from soil-borne pathogens
Another consideration is that the larger seed will produce larger cotyledons which will require more energy to push through the soil. So, in extreme conditions along with surface crusting, the larger seed could have lower emergence and reduced plant stands.
Overall, research has shown that the seed size has nearly zero impact on final stands except in extremely rare conditions. When deciding on soybean planting populations first remember that a soybean variety has the same genetic material and therefore the same yield potential regardless of the seed size. Final yield correlates to its genetic bases and the environment it is grown in that season. While seed size in extreme conditions can have a small impact on final plant stands, you will want to make sure you safeguard your plant stands from the other factors that can negatively affect your final plant populations. Soil conditions, planting depth, disease, insects, weather events, tillage, fertility, soil type, residue and planting date, just to name a few, all can impact your final stands more than the seed size.
The more you can eliminate, minimize or manage the factors that rob your emergence and potentially reduce your plant stands, the more consistent your stands will be and the higher, better yield potential you will achieve at the end of the season.