First, determine the map layers that are available. Soil texture maps are one the best places to start. If they were collected by Crop Quest these maps also include elevation and slope. Yield analysis maps also make good starter layers for VRI. In addition, some locations have access to Lidar elevation data.
Next, use a variability calculator on the layers you have available. Crop Quest consultants will do this for you at no charge if they are working with the map layers already.
Finally, take a look at the results from the calculator. In general, a field is a good candidate if using variable rate irrigation will reduce the variability by five percent or more.