Water Management in Horticultural Crops

Classification of evapo-transporation (ET)

Potential evapo-transpiration (PET)

• The term denotes the highest rate of evapo-transpiration (ET) by a short and actively growing crop or vegetation with abundant foliage completely shading the ground surface and abundant soil water supply under a given climate.
  
• It integrates the evaporating demand of the atmosphere and refers to the maximum water loss from the crop field.
Reference crop evapo-transpiration (ETo)

• The term is used to express the rate of evapo-transpiration from an extended surface of 8-15 cm tall green grass cover of uniform height, actively growing, completely shading the ground and not short of water.
  
• The ET is corrected for day and night weather conditions to ETo (adjusted reference crop ET) by multiplying with the adjustment factor.
Actual crop evapo-transpiration (ET crop)

• Refers to the rate of evapotranspiration by a particular crop in a given period under prevailing soil, water and atmospheric conditions.
  
• It involves the use of a crop factor called, crop co-efficient while computing it from reference crop ET (ETo) estimated by different empirical formulae or evaporation rates from evaporimeters.
  
• The ET crop varies under different soil, water and atmospheric conditions and at different stages of crop growth, geographical location and season of the year.