Crop water requirement
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It may be define as the water needed for raising a crop in a given period. Crop water requirement is the water required by the plants for its survival, growth, development and to produce economic parts. This requirement is applied either naturally by precipitation or artificially by irrigation. Hence the crop water requirement includes all losses like:

The water required for special purposes (WSP) like puddling operation, ploughing operation, land preparation, leaching, requirement, for the purpose of weeding, for dissolving fertilizer and chemical, etc.

Hence the water requirement is symbolically represented as:

WR = T + E + WP + WL + WSP

Where;-

1. Transpiration loss through leaves (T).
2. Evaporation loss through soil surface in cropped area (E).
3. Amount of water used by plants (WP). for its metabolic activities which is estimated as less than 1% of the total water absorption. These three components cannot be separated so easily. Hence the ET loss is taken as crop water use or crop water consumptive use.
4. Other application losses are conveyance loss, percolation loss, runoff loss, etc., (WL).
5. Water required for special purpose (WSP). like puddling, ploughing, land preparation, leaching etc.
The crop water requirement varies from place to place, from crop to crop and depends on agro-ecological variation and crop characters.