Soybean [Glycine max (L.) Merr.] yields in the United States have improved at a rate of 0.35 bu yr⁻¹ (23.4 kg yr⁻¹) since national soybean yield data was first recorded in 1924 (USDA-NASS, 2010). The consistent annual yield gain observed in soybean has been attributed to continued varietal improvement via plant breeding and the adoption of improved agronomic practices by U.S soybean producers (Specht and Williams, 1984). Previous research has found that past genetic improvements have resulted in an annual increase in soybean yield of 0.15-0.44 bu ac⁻¹ yr⁻¹ (10- 30 kg ha⁻¹ yr⁻¹), or approximately 0.5-1.0% yr⁻¹ (Specht et al., 1999). The relative contribution of genetic improvement made by soybean breeders towards overall yield gain is estimated to be 0.184 bu ac⁻¹ yr⁻¹ (12.5 kg ha⁻¹ yr⁻¹), or 50%, among hybridized cultivars released post-1940 (Specht and Williams, 1984).
Soil Science Extension
University of Wisconsin Madison