Impact of Trends in Planting Date and Phenology on Central USA Corn Productivity.

Crop yield trends, as well as their interannual variability, are affected by several factors including hybrid selection, agronomic management, pests and disease, and climate. Examining their relative contributions to historical yield increases is an important part of a process that could help ensure that yield increases continue in the future.   From previous research, we understand that “greening” of the Corn Belt since about 1980 is not entirely due to climate change, but rather arises from human land-management changes in combination with climate and other factors.  An important part of this story in the Midwest USA is the connection between long-term trend towards earlier planting of crops and long-term yield gains.  Can such knowledge help us achieve greater resiliency of cropping systems to climate change?  Here I examine long-term trends in corn and soybean planting progress and phenological development – such as length of vegetative and reproductive periods, and time elapsed between maturity and harvest – across the US Corn Belt, making use of state level USDA Crop Progress data.  These data have been used as inputs to an agroecosystem model to quantify how climate and crop management changes have impacted growing degree day requirements of hybrids, as well as energy and water balance, and contributions to yield trends.  The magnitude of earlier planting date trends (often 1-3 weeks during the 1979-2005 period) varies regionally for corn and soybean, and not all of this change can be attributed to an earlier arrival of spring or warmer springtime temperatures.   It appears that to support yield trends, producers are selecting longer season varieties to match a longer growing period length.  Most recently, advances in remote sensing science are allowing for more detailed spatial information on crop development and health that could also help increase crop resiliency to future climate change.