A multidecadal trend of earlier corn planting in the central USA

The scientific literature suggests that a trend toward earlier corn (Zea mays L.) planting has taken place over the past several decades and is largely attributed to improving technology. To substantiate this idea, analysis of two datasets were performed: (i) U.S. Department of Agriculture (USDA) weekly crop progress data from 1979 to 2005 were analyzed to quantify trends in the date that 10, 25, 50, and 75% of corn planting had been completed across 12 Corn Belt states; (ii) National Centers for Environmental Prediction (NCEP) daily climate data were studied to understand whether springtime warming was a major contributor to any observed planting date trends. Statistical analysis suggested that the initiation of corn planting (10% planted) at the state level has become earlier (P < 0.05) by 0.3 to 0.8 d yr(-1), with a regional, weighted average of 0.48 d yr(-1) earlier (P < 0.0001). The regional average planting date trends were -0.45, -0.39, and -0.37 d yr-1 for the 25, 50, and 75% planted thresholds, respectively, and all were significant (P < 0.05). Consequently, the initiation of corn planting is now averaging approximately 2 wk earlier relative to the early 1980s. Continued development of genotypes that are tolerant of suboptimal temperatures, planting equipment improvements, and adoption of time-saving management practices like conservation tillage are the more likely contributors to earlier planting rather than wide-ranging springtime warming. However, it is unrealistic to expect that this long-term trend will continue indefinitely because early planting will ultimately be limited by frozen soils.