Content area
Full text
ABSTRACT
In the United States, maize (Zea mays L.) farmers have adopted genetic-modification technology rapidly since its first commercialization in 1996. By 2012, 88% of U.S. maize is planted with genetically modified (GM) hybrids. Our objective in the paper is to present an empirical analysis of the determinants of U.S. maize yield using experimental maize production data, with a focus on the interaction effects of GM technology, management, and risk. Genetic-modification technology had a stronger impact on the lower end of maize yield distribution within a trial thereby reducing exposure to downside risk. A strong interaction exists between GM technology and crop rotations: GM reduces the adverse effects of maize-maize rotation on yield. As such, GM technology is found to be a substitute for crop rotation. Genetic-modification technology increases the yield gains associated with higher planting density. This indicates that GM technology offers good prospects for future improvements in maize productivity.
Abbreviations: GM, genetically modified; pmaize, planted after maize.
Maize productivity has increased sharply during the last few decades. In the United States, average maize yields have gone from 1.26 tons per hectare in 1930 to 7.41 tons per hectare in 1985 and to 10.29 tons per hectare in 2009 (USDA-NASS, 2012). These large productivity gains have come from both plant breeding and improved management practices, each accounting for about 50% of the increase (Duvick, 2005).
Two examples of management changes during the last 20 yr have been the adoption by farmers of more acres planted to continuous maize and an increase in plant density in production fields (Duvick, 2005). Favorable maize prices and increased demand for biofuel have promoted a trend toward maize monoculture in the U.S. Corn Belt. Increasing plant densities have contributed to higher maize yields in recent years (Duvick, 2005; Stanger and Lauer, 2006).
Over the years, breeders have selected varieties for high yield as well as greater stress tolerance. As a result, while newer hybrids give higher average yield, they also often perform better than their predecessors under unfavorable growing conditions. This trend applies to conventional hybrids as well as GM hybrids (Edgerton et al., 2012; Shi et al., 2013; Xu et al., 2013).
In the United States, maize farmers have adopted GM technology rapidly since its first...