If there is no crop coefficient value for your crop or your desired planing date is out of range, there is a generic way to estimate crop coefficient.

On a sunny day around noon time, get an estimate of how much leaf area shades the ground. For example, if your crop shades 25% of the ground based on plant and row spacing dimensions, then a rough estimate of the crop coefficient would be 0.25. However, there are three basic caveats that must accompany this procedure:

1) Use CIMIS ETo and not pan evaporation.
2) This estimated method does not apply to crops on trellises (i.e. stake tomato)
3) If the ground is wet, the soil surface looses water similar to the leaf area. Hence, any wetted surface not covered by the crop canopy estimate must be included.

Reference:

Dr. Tim Hartz

U.C. Davis Vegetable Science Department

HortTechnology 6:165-167