Irrigated agricultural production in sandy soils presents several unique challenges to growers, including naturally high permeability, low native water retention, as well as high rates of water drainage losses and leaching of chemicals to the shallow aquifers. This study is an initial investigation into water motion in the sandy agricultural soils of the Umatilla Basin, and provides a baseline data set for further research. In addition to the large in situ data set that was collected from four field sites under three different crops and two soil textures in the Umatilla Basin, several laboratory experiments were performed. Data presented in this thesis indicates that the grower at two field sites are overwatering their fields to varying degrees based on the effective field behavior, although crop need calculations and the laboratory-based soil texture analysis would indicate otherwise. Site 2 (onion) lost the most, followed by Site 1 (corn). Notably, this thesis analysis does not prove that SOM is the primary reason for higher moisture content, nor does it quantify the amount of SOM needed. However, this study opens the door to this question, and suggests the need for this type of careful analysis in sandy agricultural soils: how much SOM is needed to impact water retention properties?