Combining High-Resolution Proximal and Remote Sensing to Evaluate Intrafield Water Use in Irrigated Crop Rotations.

The growth of irrigated agriculture and decline of surface waters in sandy regions throughout the northern Great Lake states of Wisconsin, Minnesota, and Michigan has led to groundwater management and policy challenges. The Wisconsin Central Sands (WCS) is an example of an ecological region in the northern Great Lakes where increasing irrigation has severely stressed headwater streams, lakes, and wetlands. Growers are implementing precision irrigation strategies to conserve groundwater using electromagnetic induction surveys as a proxy for soil properties, despite limited data supporting these practices in humid, sandy agroecosystems.

We investigated whether WCS agroecosystems could benefit from precision intervention by comparing high-resolution apparent electrical conductivity (EC_a) maps, remotely-sensed evapotranspiration (ET) maps, and complementary ground observations to assess intrafield variability in crop water availability and use. Our research goals were to (1) assess the relationships between EC_a, particle size, and soil properties in the WCS; (2) use aerial imagery, onsite meteorological data, ground observations, and the High-Resolution Mapping of Evapotranspiration (HRMET) model to create high-resolution maps of ET for key WCS crop rotations; and (3) identify persistent infrafield differences in ET, EC_a, and soil properties that would support precision irrigation interventions across different crop rotations.

Our findings suggest that proximal sensing of EC_a is a promising approach for identifying intrafield variability in soil properties throughout the WCS, despite coarse soils and extremely narrow EC_a ranges. We also demonstrated the utility of a combined high-resolution EC_a and ET mapping approach to quantify intrafield variability in water use over different crop rotations. By quantifying intrafield relationships between EC_a, soil properties, and ET, we found that not all crop rotations on a given field will respond equally to precision irrigation. However, further studies are needed to assess long-term water savings, water use efficiency, and yield potential of precision irrigation interventions in the WCS.