Groundwater levels in the Mississippi Delta have declined more than 6.4 meters (20 feet) since 1970 due to extraction to irrigate agricultural crops. More on-farm water storage ponds have been constructed in recent years in Mississippi, but the optimal ratio of pond size to irrigated crop land area was not known. It is crucial to know how many hectares (1 hectare = 2.47 acres) of crop land can be irrigated with one-hectare of pond water in order to cost-effectively construct the proper size pond, manage pond water for crop irrigation, and mitigate groundwater depletion in Mississippi and in other regions of the U.S. facing similar issues. Scientists from the Forest Service and the Agricultural Research Service, agencies within the U.S. Department of Energy, developed a modeling tool using the STELLA (Structural Thinking, Experiential Learning Laboratory with Animation) software to determine the ratio of pond size to irrigated soybean land for a pond that represented the average conditions in east Mississippi and the Mississippi Delta. One simulation shows that a reasonable ratio of pond size to irrigated soybean land is 1:18, if the scheduled irrigation rate is 2.54 centimeters (1 inch) per day, the average pond depth is 1.83 meters (6 feet), and the pond water level is drawn down to 0.38 meters (1.25 feet). A maximum ratio of 1:20 is possible if the pond water level is drawn to near zero. Using the ratio of 1:18, a one-hectare soybean field could save about 542 cubic meters (143,181 gallons) of groundwater each year. Results suggest that an on-farm water storage pond is a promising approach to conserve groundwater resources. The model and findings from this project could have substantial impacts on 1.82 million hectares (4.50 million acres) of crop land in Mississippi. Other regions of the U.S. with similar groundwater management challenges would also benefit from using this predictive tool.