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AGROCLIMATOLOGY

Contribution of Planting Date Trends to Increased Maize Yields in the Central United States

Center for Sustainability and the Global Environment (SAGE), The Nelson Institute for Environmental Studies, 1710 University Avenue, Univ. of Wisconsin, Madison, WI 53726

^* Corresponding author (kucharik{at}wisc.edu).

Early planting of maize (Zea mays L.) allows for longer-season hybrids to be used in cool temperate regions. Given that a multidecadal trend toward earlier planting has been occurring across the Corn Belt, it was hypothesized that this shift has supported a portion of recent yield increases. The objectives were to quantify relationships among state level monthly climate variables, maize yields, and planting dates, and to investigate whether multidecadal trends of earlier planting contributed to rising yields during 1979 to 2005 in 12 central U.S. states. Year-to-year changes (i.e., first differences) of predictor variables (monthly mean temperature and precipitation and planting date) and yields were calculated, and multiple linear regression was used to estimate the effect of planting date trends on maize yield increases. In six of the 12 states, a significant relationship (P < 0.05) existed between first differences of planting dates and yields. Multiple linear regression suggested that the management change has potentially contributed between 19 and 53% of the state level yield increases in Nebraska, South Dakota, Minnesota, Iowa, Wisconsin, and Michigan. Yield increases between 0.06 and 0.14 Mg ha^–1 were attributed to each additional day of earlier planting, which likely reflects a gradual adoption of longer-season hybrids. Thus, if these earlier planting trends were to suddenly abate, a falloff in annual yield increases may follow in several Corn Belt states. Maize production in northern U.S. states appears to have benefited more significantly from earlier planting due to a shorter growing season in contrast to more southern locations.

Abbreviations: DOY, day of year • GDD, growing degree days • USDA, United States Department of Agriculture • NASS, National Agricultural Statistics Service

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Received for publication April 18, 2007.