Crop Water Use (ET)

Crop evapotranspiration estimates how much water a specific crop will lose to the atmosphere through evaporation from the soil and transpiration from the plant. The crop coefficient, Kc, scales a standard reference evapotranspiration value to account for the crop type, growth stage, canopy cover, and local management conditions, so the product gives a practical estimate of crop water demand. It works because reference ET represents the atmospheric demand under well-defined standard conditions, and Kc adjusts that demand to the real crop surface.

Use this when planning irrigation for a field crop, orchard, pasture, or greenhouse crop and you have a reference ET value from weather data. It is also useful in water budgeting, irrigation scheduling, and comparing water requirements across growth stages or crop varieties.

• Using ET_c directly as irrigation depth without accounting for rainfall, soil storage, or irrigation efficiency
• Mixing units, such as combining ET_0 in inches with K_c values calibrated for millimetres
• Applying a single K_c value without considering the crop growth stage or recent canopy changes