Evapotranspiration and agriculture-A review

Evapotranspiration (ET), an important component of hydrologic cycle, represents energy interaction between hydrosphere, atmosphere and biosphere. As the term indicates, it combines two processes-evaporation and transpiration. Evaporation is a diffusive process which transfers moisture in the form of vapour from the earth surfaces such as wetted soil mass, plant canopy, open water surface and other moist or wet natural surfaces. The transpiration converts liquid water into vapour form from the tissues of various plant parts such as leaf, stem, flowers, and or roots. The ET process serves as significant contributor of moisture back in to the atmosphere. Sun is the ultimate driving force for this process, exposure of the evaporating surface determines the rate of ET. The major sector of water use in the global as well as local scale, the agriculture sector is highly dependent on the concept of ET for irrigation scheduling. ET based irrigation scheduling is getting wider applications as a means to improve water productivity due to rising concern on water conservation. The environmental demand for water regulates the water requirement of the crops. The process is controlled by other factors like amount of ground coverage by the crops and its geometry, growth stage of the plant, nature and characteristics of the ground surface etc., apart from the meteorological parameters. The concept of reference ET gained importance in agricultural water requirement estimation. The present chapter focuses on the basic concepts and developments of ET and reference ET and their applications in the agriculture sector.