⏱ Irrigation Scheduling

Irrigation Scheduling

“Irrigation scheduling is the process of determining when to irrigate and how much water to apply”.

👉🏻 Why Need of Irrigation Scheduling

1. For maximize water use efficiency
2. To maximize yield
3. To increase cropping intensity
4. Improve and quality produce
5. To maintain soil and environmental balance

👉🏻 Purpose of Irrigation Scheduling

“To maximize irrigation efficiency by applying the exact amount of water needed to replenish the soil moisture to the desired level.”

👉🏻 Effect of Poor Scheduling of Irrigation

1. Non efficient use of irrigation water and production inputs i.e. fertilizers
2. Lower crop yield
3. Decrease in production per unit of water

👉🏻 Scheduling of Irrigation is Based on

1. When to irrigate
2. How much to irrigate

When to Irrigate

1. More nutrient availability and most crops taken up water when soil moisture is near field capacity
2. Maximum production when irrigation is given at 50 per cent soil moisture content in root zone of the crop
3. Determination of soil moisture content by:

• Gypsum block
• Tensiometer
• Gravimetric method

How much to Irrigate

• It is the net quantity of water to be applied.
• The quantity of water given for irrigation is depend upon the amount of available moisture in the soil.

Approaches of Irrigation Scheduling

1. Soil moisture depletion approaches
2. Climatological approaches
3. Plant approaches

Soil Moisture Depletion Approaches

• The available soil moisture is between field capacity (-1/3 bar) to wilting point (-15 bar).
• For crops like wheat, rice, maize - 25 per cent depletion of available soil moisture is adequate.
• For drought resistant crop like sorghum, bajra, cotton - 50 per cent depletion of available soil moisture is adequate.
• Irrigation water applied at a predetermined soil moisture tension at a specific depth by tensiometer at 0.85 bar.
• Soil moisture content is estimated by farmers by feel and appearance of soil condition.

Climatological Approaches

👉🏻 Irrigation Water/Cumulative Pan Evaporation ratio (IW/CPE ratio)

• The use of IW/CPE ratio is suggested as a practical basis of scheduling irrigation. The approach is based on the close and direct relationship of crop evapotranspiration with pan evaporation. When irrigation is applied, water is lost from the soil through evapotranspiration in the same way as the evaporation occurs from an open pan evaporimeter. It is ratio of the amount of irrigation water (IW) applied to cumulative pan evaporation (CPE).
• The pan evaporation values are added up every day till it is equal to certain ratio of the amount of water applied as irrigation. The ratio for various crops is determined experimentally by estimating the evapotranspiration by lysimeter studies.
• The IW/CPE ratios for various crops at different agro-climatic conditions in India have been determined under ICAR Coordinated Project for Research on Water Management.
• A fixed 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 (5 cm is most common).
• Irrigation scheduled at IW/CPE ratio of 1 with 5 cm of IW means 5 cm of irrigation water is applied when cumulative pan evaporation reaches 5 cm.
• This technique is simple, rapid, reliable and has high extension value.

Plant Approaches

Any plant character relative directly or indirectly to plant water deficit which respond readily to influence soil water, plant and evaporation demand of atmosphere may serve as a criterion for timing of irrigation to plant.

• Indicator plant: The plant under moisture stress indicates the change in colour of leaf i.e. Cotton, beans, groundnut, alfalfa etc. Sunflower show wilting symptoms.
• Relative water content
• Leaf water potential
• Plant temperature
• Water diffusion resistant
• Computer modelling
• Cell elongation rate

But these methods require extensive research, expensive equipment and standardization.