Study area and its location in Nebraska and the USA.

<p>Location of Nebraska in the map of the USA (red area in the upper-left map), location of the study area in the Central Platte NRD and the Tri Basin NRD in the map of Nebraska (blue and green areas in upper-middle map), and fields (yellow points) and weather stations (blue triangles) in the study area (main map). The study area in the main map is divided into blue, green and red areas. Those colors represent groundwater quality management areas, which depend on the nitrate concentration in the groundwater. Blue areas in the main map represent phase 1 areas, where nitrate concentrations are acceptable. Green and red areas are phase 2 and phase 3 areas, where nitrate application is regulated by the respective NRD.