Could Precision Irrigation Conserve Groundwater in the Humid, Sandy Aquifers of the Northern Great Lakes States?.

The Northern Great Lakes States (NGLS) of Wisconsin, Michigan, and Minnesota are known for their humid climate, coldwater trout streams, and rapidly expanding irrigated vegetable industries. As water scarcity and climate change continue to disrupt vegetable production the Western United States, comparatively resilient regions such as the NGLS bear increasing stress to produce more vegetables, while preserving surface waters. Precision irrigation is gaining momentum as a solution that tackles both intensification and conservation challenges, but its current implementation in the NGLS is based on technologies developed for arid climates. In humid climates, precision irrigation needs to optimize unpredictable precipitation in order to reduce consumptive groundwater use. Growers and agribusinesses in the NGLS are experimenting with precision strategies that use apparent electrical conductivity (EC_a) to delineate irrigation management zones for variable rate applications. Though this strategy has been effective in arid agroecosystems, there are limited experimental data supporting these practices in the NGLS, which makes it difficult to assess return on investment. We partnered with a sixth-generation family farm growing irrigated vegetables in the NGLS to quantify the spatial relationships between of soil texture, crop phenology, and water use from four conventionally managed agroecosystems. We used high-resolution maps of EC_a and point-based measurements of soil texture, leaf area index, ET, soil moisture storage, and deep drainage to assess the potential for zone-based irrigation management in the NGLS. Preliminary results reveal significant correlations between mapped EC_a, soil texture, ET, and consumptive groundwater requirement that could be further optimized for precision irrigation in humid, sandy agroecosystems. However, the strength of these relationships depended on the specific field, crop rotation, precipitation regime, and evaporative demand in a given growing year. Future work will use these relationships to build models and quantify potential groundwater savings from precision irrigation at regional scales.