Changes in crop productivity as a result of shallow groundwater, Yahara Watershed, Wisconsin

A primary limitation on agricultural yields in many parts of the world, including the US Corn Belt, is the quantity and temporal distribution of water resources. Shallow groundwater can have a significant positive influence on production by providing water during times of drought. To examine the influence of shallow groundwater over crop output, we studied groundwater levels, soil moisture dynamics, and crop performance metrics in a commercial corn field in the Yahara Watershed of south-central Wisconsin. A trend of increasing precipitation over the past 80 years has altered the local water balance and caused groundwater flooding in many fields over the northern part of the basin. Analysis of historical imagery shows that the field has been home to several ephemeral water features over the past half-decade, indicating a water table likely near the root zone.

The 2012 growing season of southern Wisconsin was characterized by atypical heat and drought through June and much of July, a period which includes the critical reproductive periods of tasselling and silking for most of the county’s corn. Preliminary results for the 2012 growing season show that shallow groundwater has provided a significant benefit to crops located in low-lying areas of the field during the drought period, though variation in soil type over the field may have a confounding influence. Measures of overall plant vitality (such as leaf area index, length of the longest leaf, and plant height) were higher in sections of the field where shallow groundwater was accessible. More importantly for grain yield, cob diameter also increased faster and grew larger in sections of the field with shallow groundwater. Thermal imaging showed that, during the drought, increases in leaf surface temperature in areas with deep groundwater occurred in conjunction with decreases in stomatal conductance, indicating a reduction of evapotranspiration due to water stress. Forthcoming end-of-season biomass, grain moisture content, and harvest index measurements over the field will be used in conjunction with these data to investigate the positive growth potential associated with shallow groundwater availability during times of drought.