Seeding rate effects on soybean seed yield components and economic return

Soybean ( Glycine max [L.] Merr.) seed prices have increased by more than 190% from 1998 to 2018 in the US, making seeding rate one of the most cost‐sensitive management decisions. While soybean can maintain maximum seed yield across a wide range of plant populations due to their morphological and reproductive plasticity, the decreasing commodity prices and increased seed cost necessities re‐evaluation of economic optimum seeding rates. This study aimed to evaluate soybean yield responses and economic return across a wide range of seeding rates and environments in Iowa, as well as seed quality. Across site‐years, the agronomic optimum seeding rate (AOSR) was 234,300 seeds ha −1, where seed yield plateaued at 4.7 Mg ha −1 . Results showed a higher number of pods and seeds at seeding rates lower than 234,300 seeds ha −1 ; however, at higher seeding rates, the number of pods and seeds were consistently lower. There was no relationship between individual seed weight, oil and protein content, and seeding rates. Seeding rates above the AOSR resulted in no benefit under favorable conditions, since higher plant populations mostly benefit environments exposed to weather events that reduce population (e.g., hail). The economic optimum seeding rate (EOSR) averaged approximately 90.8% of the AOSR. Seed yields are maximized by targeting the AOSR; however, the additional yield from the difference between AOSR and EOSR did not bring financial gains.