Technical Abstract: The ability to determine how long a crop utilizes a given amount of water either from an applied irrigation or a precipitation event would have great potential in improving irrigation decision systems. This would be true particularly for peanut growers since over 50% of all U.S. peanut production is irrigated and has the potential to increase yields by 19% over dryland production. We attempted to quantify water movement through soil and peanut plants in two soil types in southwest Georgia: Tifton sandy loam and Greenville clay loam. During the active growth phase (~ 80 days after planting), deuterium labeled water was applied to peanuts growing in both soils simulating a typical irrigation or rainfall event experienced by peanut plants. Soil at four depths and stem tissue was collected after the deuterium was applied. The first experiment in Greenville soil was conducted over a 24 hour period in order to determine how much of a rainfall or irrigation event was utilized in a fully charged soil profile. The second experiment in Tifton soil was conducted over a four-day period starting with a relatively dry soil profile in order to determine how long a peanut plant could utilize an irrigation or rainfall event over a time period that would be typical between irrigation applications in this region.