Water Management in Horticultural Crops

3.Penman formula

• Penman (1948) suggested a formula using the important climatic parameters such as solar radiation, temperature, vapour pressure and wind velocity to compute the evaporation from open free water surface.
  
• Estimates of crop ET are obtained by multiplying the estimated values of evaporation by crop coefficient.
  
• Doorenbos and pruit (1975) proposed a modified penman method for estimating fairly accurately the reference crop ET and gave tables to facilitate the necessary equation.
  
• The penman method is quite satisfactory for both humid and arid regions under calm weather conditions. It has the advantage over other two methods as it uses many climatological parameters for the estimate of crop ET.
  
• Drawbacks are that the method requires many climatological parameters that may not be available in many meteorological stations and the computation procedure is cumbersome.