The Realized Yield Effect of Genetically Engineered Crops: US Maize and Soybean

Yield improvements are critical to ensuring food security for a growing world population especially in view of the increasing potential for use of land in biofuel production. Efforts to sustain the impressive rate of past productivity gains, epitomized by such successes as the Green Revolution, are bound to rely on biotechnology innovations such as those responsible for the development of genetically engineered (GE) crops. Some argue that the use of biotechnology can substantially improve yields relative to the trajectory established by traditional breeding in the 20th century. Because U.S. adoption of GE varieties has been very strong since their introduction in the late 1990s, we investigated empirically whether and to what extent the GE technology has improved realized yields. We study this question for nonirrigated U.S. maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields over 1964 through 2010, having controlled for local effects, weather, fertilization, and the preexisting (non-GE) crop improvement trend. For maize we find that GE varieties have increased realized yields, with a stronger gain in the Central Corn Belt (CCB). For soybeans, GE varieties appear to have slightly reduced yields. For both crops we find a strong trend in yield growth, which may have accelerated in recent years within the CCB. However, the combined effects of yield trend and GE adoption are predicted to fall short of the growth rate envisioned by industry projections.