LPM 121: Fodder Production and Grassland Management (1+1)

DIFFERENT APPROACHES FOR IRRIGATION SCHEDULING

• Soil moisture depletion approach
• Climatological approach
  • IW / CPE approach
  • Can evaporimetry method
  • Combination approach
• Critical stage approach

Soil moisture depletion approach

• When the soil moisture in a specified root zone depth is depleted to a particular level, it should be replenished by irrigation.
• Eg. Irrigation can be scheduled at 25% depletion of soil moisture for crops like maize, wheat etc. and at 50% depletion of soil moisture for crops like sorghum, pearl millet, finger millet etc.

Climatological approach

• This is mainly based on evapotranspiration. Based on the climatic data different methods are employed.
• IW/ CPE approach
  • A known amount of irrigation water is applied (IW) when the cumulative pan evaporation reaches a predetermined level.
• Can evaporimetry
  • Small cans of one litre capacity painted white and covered with 6/20-size mesh are used to indicate evaporation from the cropped field.
  • An indicator point 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 kept to 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 and can is again filled to the pointer level.
• Combination approach
  • This is based on soil moisture depletion and climatological approach for sufficient and deficit irrigation water conditions.

Critical stage approach

• In each and every crop, there are certain growth stages at which moisture stress leads to irrevocable yield loss and these stages are known as critical period or moisture sensitive period. This is highly suitable under limited water supply conditions. Here the irrigation is scheduled at moisture sensitive stages and irrigation is skipped at non-sensitive stages.
• For higher water use efficiency by a crop, application efficiency, storage efficiency and distribution efficiency, different methods of irrigation can be followed based on land slope, amount of water and equipment available, crop and method of cultivation of crop.