Estimation of Aeration Stress Effects On Crop Yields in Midwest USA.

Soil moisture condition during the growing season is closely related to crop yields. Excess soil moisture results in a deficiency of oxygen and increase of carbon dioxide in the root zone, resulting in leaf chlorosis and reduced growth, especially in the early growing season. The potential for excess water can be widely found in the Midwestern US, where poorly drained soil contributes to a high water table. Subsurface drainage is commonly used to make such fields workable, however, the increasing precipitation and a move towards growing biofuel feedstock crops on marginal lands means that the potential adverse impacts of aeration stress on the crop yields need to be critically evaluated.

The main objective of this study is to explore the ability of an existing hydrology and crop growth model (SWAT 2009) to simulate yield variability for traditional crops (corn and soybeans) in the Midwestern US with respect to observed climate and soil moisture variability. Layer specific soil moisture contents were obtained from the NRCS-Soil Climate Analysis Network (SCAN) at four sites in Illinois, Ohio and Iowa. Sensor observed daily soil moisture data were first bias corrected by considering the porosity of each layer, and then integrated to a value representing the whole soil column Detailed soil information (field capacity, bulk density, etc) from soil pedon reports at each SCAN site were used to formulate model soil inputs. SWAT 2009 was calibrated and evaluated using the observed soil moisture from each site. The calibrated model was then used to extend the observational record between 1940-2010 to better capture the effects of climate variability on crop yields.  The model was used to predict soil moisture, growth stress factors (aeration, drought and temperature stresses) and crop yields. Simulated results were compared with county level crop yield data (USDA-NASS) to quantify crop yield sensitivity to variations in climate, especially under conditions leading to substantial aeration stress.