Plot-scale modeling of soil water dynamics and impacts of drought conditions beneath rainfed maize in Eastern Nebraska

Intermittent drought periods pose major challenges to the management of rainfed agricultural systems because their productivity is sensitive to water stress during crop development. The objective of this study was to assess soil water dynamics and crop stress patterns during the drought year of 2012, which was among the most severe on record in the US Corn Belt. The study utilized a continuous matric potential profile monitoring record from June 2008–December 2012 beneath a rainfed corn plot in Eastern Nebraska to provide a direct comparison of the 2012 growing season with moderate to relatively wet periods within 2008–2011. The analysis was based on a transient unsaturated zone model that was calibrated with laboratory-measured water retention functions and matric potential measurements from heat dissipation sensors. In each year of the model simulation, soil water storage volumes steadily decreased during the growing season and increased episodically following precipitation events outside of the growing season. Precipitation during the 2012 growing season was <50% of the mean for growing seasons 2009–2012 consequently, soil water storage loss during 2012 was ∼14% of initial storage in comparison to 8–9% in 2009–2011. Model results suggest that the 2012 soil water deficit was partially buffered by upward flux of deep soil moisture, with approximately 17% of root water uptake in 2012 deriving from moisture redistributed from below the root zone. Nevertheless, root zone matric potentials exceeded the crop wilting point (ψ=−8000cm) in 2012 for the first time within the monitoring record. These results highlight the need for heightened attention to drought resilience of rainfed cropping systems given future climate predictions that involve increase rainfall intermittency.