The consumptive use of water by crops is synonymous with the term evapotranspiration.
Consumptive use is expressed as a volume of water per unit area, annual acre-feet per acre.
It is a measure of the water transpired by plants, retained by plant tissue and evaporated from adjacent soil surface over a specific period of time. The higher the temperature and wind, and the lower the humidity, the greater the evaporation. When there is insufficient water for the plant, the stomates close. The gas exchange cannot occur and plant growth decreases. Alfalfa, for instance, increases in need from the 10-20th day after cutting until it levels off until the next cutting.