Seed Size vs Yield - What Farmers Should Really Know

By Blake Jackson

Does increasing seed size automatically increase yield? At first glance, the universal yield equation—yield = (seeds per acre × weight per seed)—might suggest that larger seeds should always produce higher yields. However, according to Dr. Dennis Egli, Professor Emeritus at the University of Kentucky, the relationship is far more complex.

A key question is whether differences in seed size are driven by genetics or environmental conditions. Across crop species, seed size varies widely.

For instance, canola produces extremely small seeds (about 43,560 seeds per pound), while corn seeds are much larger (around 1,574 seeds per pound). Even within a species, genetic differences in seed size are common, but these differences generally do not translate into higher yields.

In crops like wheat, high yields can be achieved even with relatively small seeds. This is because many genetic differences in seed size are linked to seed growth rate rather than total productivity. Larger seeds often grow faster, while smaller seeds grow more slowly.

Faster growth tends to reduce the number of seeds per acre, while slower growth increases seed number, balancing overall yield. As a result, simply selecting varieties with larger seeds does not guarantee improved yield.

There are exceptions, however. When larger seed size results from a longer seed-filling period rather than faster growth, yield can increase. In these cases, seeds accumulate more resources over time, leading to both larger seeds and higher productivity.

Environmental conditions during seed development play an even more important role. Once the number of seeds per acre is set, usually before seed filling begins, environmental factors influence final seed size.

Favorable conditions, such as adequate rainfall and moderate temperatures, can increase seed size and yield. In contrast, stress from drought, disease, or heat during seed filling can significantly reduce both.

Research shows even brief stress periods can have measurable effects. In soybean greenhouse studies, just three days of water stress during seed filling reduced seed size by 13% and yield by 17%.

Ultimately, yield is not finalized until physiological maturity. Seed size–yield relationships depend on both genetics and environment, but environmental conditions during seed filling often determine the final outcome.

Photo Credit: gettyimages-studio2013