Crop water requirement table, afo questions, ICAR UG syllabus, Water requirement of important crops pdf, crop water requirement, crop requirement formula
Definition of crop water requirement
Crop water requirement is the water required by the plants for its survival, growth, development and to produce economic parts.
Crop water requirement formula
This requirement is applied either naturally by precipitation or artificially by irrigation. Hence the crop water requirement includes all losses like:
• Transpiration loss through leaves (T).
• Evaporation loss through soil surface in cropped area (E).
• 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.
• Other application losses are conveyance loss, percolation loss, runoff loss etc., (WL).
• The water required for special purpose (WSP) like puddling operation, ploughing operation, land preparation, leaching requirement, for the purpose of weeding for dissolving fertilizers and chemicals etc.
Hence, the water requirement is symbolically represented as:
WR = T + E + WP + WL + WSP
Based on supply of source this equation can be rewritten as
WR = IR + ER + S
Where,
IR – Irrigation requirement
ER – Effective rainfall
S – Contribution from groundwater table.
The combined loss of evaporation and transpiration from a cropped field is termed as evapotranspiration, which is otherwise known as consumptive use and denoted as ET and this is a part of water requirement.
CU = E + T + WP
Therefore, WR = CU + WL + WSP
Alternate definition of crop water requirement
The crop water requirement can also be defined as water required to meet the evapotranspiration demand of the crop and special needs in case of wet land crop and which also includes other application losses both in the case of wet land and garden land crops. This is also known as crop water demand.
Factors affecting water requirement
The crop water requirement varies from place to place, from crop to crop and depends on agro-ecological variation and crop characters. The following features
which mainly influence the crop water requirement are:
- Crop factors – Variety, growth stages, duration, plant population and crop growing season.
- Soil factors – Structure, texture, depth, topography and soil chemical composition.
- Climatic factors – Temperature, sunshine hours, relative humidity, wind velocity and rainfall.
- Agronomic management factors – Irrigation methods used, frequency of irrigation and its efficiency and tillage and other cultural operations like weeding, mulching etc.
Crop water requirement classification
Based on all these factors, average crop water requirement for various crops have been worked out and given below for tropical conditions. In general, this crop water requirement can be classified as:
- Low ranging from 300-450 mm green gram, black gram, sunflower, safflower, finger millet and minor millets.
- Medium ranging from 450-650 mm maize, sorghum, wheat, groundnut and sunflower.
- High ranging from 600-1000 mm cotton and perennial red gram.
- Very High ranging from 1000-2250 mm rice, sugarcane, banana and plantation crops.
Crop water requirement for important crops
| Crop | Water requirement in mm range |
|---|---|
| Rice | 1200 to 1400 mm |
| Maize | 400 to 550 mm |
| Sorghum | 400 to 550 mm |
| Wheat | 450 to 550 mm |
| Ragi | 350 to 550 mm |
| Pulses | 350 to 450 mm |
| Groundnut | 350 to 650 mm |
| Sunflower | 300 to 500 mm |
| Cotton | 600 to 850 mm |
| Sugarcane | 1400 to 2000 mm |
| Banana | 1650 to 2250 mm |
| Plantation crops | 1250 to 1850 mm |
Relation between irrigation requirement and water requirement of crop
IR = WR − (ER + S)
Where,
IR = irrigation requirement
WR = water requirement
ER = effective rainfall
S = soil moisture contribution
5 crops which require less water
5 crops that require less water are Millet crops, Sorghum, Pulses, Groundnut, Bajra
Crop with the highest water use efficiency is
Finger millet has the highest water use efficiency of 13.4 kg per hectare mm
International Water Management Institute IWMI is located at Colombo, Srilanka it is a CGIAR institute.
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