Two independent water balance approaches demonstrate extensive use of groundwater by rainfed crops

Authors: Schreiner-Mcgraw, Adam; Baffaut, Claire

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2026
Publication Date: 2/10/2026
Citation: Schreiner-Mcgraw, A.P., Baffaut, C. 2026. Two independent water balance approaches demonstrate extensive use of groundwater by rainfed crops. Agricultural Water Management. 326. Article 110218. https://doi.org/10.1016/j.agwat.2026.110218.
DOI: https://doi.org/10.1016/j.agwat.2026.110218

Interpretive Summary: Crop growth fundamentally depends on water availability in the root zone. While it is known that annual grain crop roots extend beneath the shallow topsoil and into shallow groundwater, it is not known where in the soil profile crops draw water from, or to what extent they use groundwater. In this study, we co-located measurements of crop water use, soil moisture profiles, and groundwater level at three locations within a field that is managed with alternative practices to improve sustainability (ALT field) to quantify where in the subsurface crops draw water from. We find that crops primarily draw water from the topsoil (top 10-30 cm) and shallow groundwater, accounting for an average of 27% and 53% of growing season water use, respectively. To test if our results were representative of common agricultural practices in the region, we calculated groundwater use at the ALT field, and a field following the prevailing management practices in the region (PRE). We found that both fields had considerable crop water use sourced from groundwater; an average of 71 mm and 98 mm per growing season for the PRE and ALT fields, respectively. These observations highlight the importance of groundwater in rainfed croplands in the U.S. Corn Belt.

Technical Abstract: In the rainfed cropland of the U.S. Corn Belt understanding crop water use is important to adapt management practices to a changing climate. Changing precipitation patterns are expected to affect distributions of soil water, vadose zone water, and groundwater in complex ways. Thus, quantification of where in the subsurface crops extract water from is warranted. In this study, we co-located measurements of crop water use, soil moisture profiles, and groundwater level at three locations within a field (ALT field) with a restrictive claypan soil layer to quantify where in the subsurface crops drew water from. We found that crops primarily drew water from the topsoil (top 10-30 cm) and shallow groundwater, accounting for an average of 27% and 53% of growing season water use, respectively. Groundwater use was calculated as a residual of the water budget, so measurement uncertainty likely biased our results. Additionally, there was considerable variability between the three locations, likely due to differing water table depths. To test if our results are robust over a longer period, we calculated field-scale water budgets using measurements of precipitation, evapotranspiration (ET), and runoff at the ALT field, managed with alternative practices to boost sustainability, and a field following the prevailing management practices in the region (PRE). We found that both fields had considerable ET sourced from groundwater; an average of 71 mm and 98 mm per growing season for the PRE and ALT fields, respectively. These observations highlight the importance of groundwater in rainfed croplands in the U.S. Corn Belt.