a) Soil moisture depletion approach
b) Physical stage or critical stage approach.
c) Leaf water potential
d) Irrigation scheduling based on calculations.
- Soil moisture depletion approach
- The available soil moisture in the root zone is a good criterion for scheduling irrigation.
- When the soil moisture in a specified root zone is depleted to a particular level (which is different for different crops), it is to be replenished by irrigation.
- For crops like maize, wheat etc. scheduling irrigation at 25% depletion of available soil moisture is adequate. For drought resistant crops lime sorghum, pearl millet, finger millet, cotton etc.
- It is coefficient to irrigate at 50% depletion of available soil moisture.
- Physical stage or critical stage approach
Critical stages of water requirements
|
Crop |
Physiological stages |
|
Rice |
Tillering, flower primordial formation,flowering, milk and dough |
|
Wheat |
CRI, tillering, milking and dough |
|
Maize |
Early vegetative growth, tasseling, silking and dough |
|
Sorghum |
Seedling, flowering and dough |
|
Barley |
Early vegetative, flowering and dough |
|
Oat |
Ear emergence |
|
Finger millet |
Flowering, grain formation |
|
Soyabean |
Early seedling, flowering, pod development |
|
Potato |
Stolonization, tuberization and bulking |
|
Sugarcane |
Emergence, tiller initiation, tillering, elongation |
|
Groundnut |
Emergence, flowering, pod formation, pod development. |
|
Tobacco |
Topping |
- Irrigation scheduling based on calculations
Or IW/CPE ratio approach
- IW/CPE approach a known amount of irrigation water (IW) is applied when cumulative pan evaporation (CPE) reaches a predetermined level.
- The amount of water given at each irrigation ranges from 4-6 cm, the most common being 5 cm of irrigation.
- Scheduling irrigation at an IW/CPE ratio of 1.0 with 5 cm of irrigation water means 5 cm of irrigation water is applied when the cumulative pan evaporation reaches 5 cm.
- Can evaporimeter approach
- In this small can of one liter capacity (14.3 cm height and 10 cm diameter) are used to indicate evaporation from the cropped field.
- These cans are painted white and covered with 6/20 size mesh. An indicator pointer is fixed at 1.5 cm below the brim.
- When irrigation is given bringing the soil to field capacity, the can is filled up with water to pointer level and ke pt at the crop height.
- Evaporation from can is directly related to crop evapotranspiration.
- Irrigation is scheduled when the water level in the can falls to a predetermined level (equal to the amount of water to be applied at each irrigation) and can is filled again to the pointer level.
