The year 2025 might turn out to be the year of the ‘small seeds’. Some producers harvested seeds that are smaller than normal. The explanation for this phenomenon lies in the interaction between the vagaries of the weather and the stage of crop development.
This year started out as a good year (rainfall in Kentucky from January through July was above normal, according to Matt Dixon, Senior Meteorologist in the Ag Weather Center, raising hopes for good yields, but the bottom dropped out when it stopped raining in August. This August was the driest on record (total rainfall for the month was 1.29 inches, 2.5 inches below normal); September was better, but there were still areas in the state with below normal rainfall. If the dry weather hit when corn and soybean crops were filling their seeds, the seeds would be smaller than normal.
Dividing yield into its two components – the number of seeds per acre and the weight per seed (seed size) – helps us understand this relationship. The number of seeds the crop produces is determined by the productivity of the environment during flowering and seed set (Growth stage R1 to R5/R6 in soybean and roughly 20 days before and after silking in corn). A highly productive environment (no water stress or other limitations) during this critical period will produce a large number of seeds, while stress will reduce seed number by interfering with pollination or causing extra abortion of flowers and immature seeds.
The productivity of the environment during the seed-filling period will affect final seed size. A highly productive environment will produce large seeds, but water stress during seed filling will accelerate leaf senescence, shorten the seed-filling period, and reduce seed size. This probably happened in some fields in Kentucky that ran out of water during seed filling. A potentially high yield, assuming seed set occurred before the water ran out, was not realized because of stress during seed filling.