Irrigation & Drainage management

Measurement of Irrigation Water

Measurement of Water Height

Conversion Units

Classification of Ploughing (CRIDA, Hyderabad 1985)

Watershed Management

🔹 Definition: A watershed is a natural unit of land where runoff collects and drains through a common outlet like a stream or river.

🔹 Classification (based on area):

Irrigation

Definition: Artificial application of water to the soil to meet crop evapotranspiration (ET) needs.

Methods of Irrigation

a) Surface Irrigation (Most common in India)

• Most common surface method in India: Check Basin Irrigation
• Best method for row crops: Furrow Irrigation
• Most water-wasting method: Flood Irrigation
• Best for orchards: Ring Basin Irrigation
• Slope-dependent method: Border Strip Irrigation

b) Sub-Surface Irrigation

• Definition:: A method of irrigation in which water is applied below the soil surface directly to the root zone through buried pipes, tiles, or perforated conduits.
• Working Principle:: Water moves upward by capillary action, supplying moisture to roots without wetting the soil surface, thus minimizing evaporation losses.

Regions & Crops:

• Kerala: Coconut
• Gujarat & Kashmir: Vegetables, orchards
• Used mainly for high-value crops

Soil & Land Requirement: Sandy loam soils. Uniform soil profile. Level or gently sloping land

Advantages:

• Very low evaporation loss
• Reduced weed growth
• No surface waterlogging
• Maintains optimum soil moisture
• Efficient nutrient uptake

Limitations:

• High initial cost
• Difficult to detect clogging or leakage
• Not suitable for heavy clay soils
• Requires skilled maintenance

Exam Points:

• Based on capillary rise principle
• Highly efficient but limited adoption
• Useful where surface irrigation is difficult

ii) Sprinkler Irrigation System

Definition: Sprinkler irrigation is a pressurized irrigation system that simulates natural rainfall by spraying water through nozzles over the crop.

Working Mechanism:: Water is pressurized by pumps, conveyed through pipes, and sprayed uniformly over crops through sprinklers.

Technical Parameters (MCQ Important):

• Pressure: 2.5–4.5 kg/cm²
• Discharge rate: >1000 L/hr
• Water saving: 25–50%
• WUE: ~60%

Suitable Conditions:

• Undulating or uneven land
• Light to medium soils
• Crops: wheat, vegetables, fodder, oilseeds

Advantages:

• Suitable for irregular topography
• Prevents soil erosion
• Saves 40–60% labour
• Uniform water application
• Protects crops from frost and heat stress
• Allows fertigation

Limitations:

• Not suitable for rice
• Inefficient on heavy clay soils
• High energy requirement
• Wind affects water distribution

Exam Points:

• Operates at higher pressure than drip
• Reduces runoff and deep percolation
• Widely used in water-scarce areas

Drip (Trickle) Irrigation

• Definition: Drip irrigation is a micro-irrigation method in which water is applied slowly and directly to the root zone through emitters.
• Origin: Introduced from Israel; widely adopted in India under micro-irrigation schemes.
• Working Principle: Water drips at low pressure near the root zone, minimizing evaporation and runoff losses.

Technical Parameters (Highly Important):

• Pressure: 1.5–2.5 kg/cm²
• Discharge rate: 1–8 L/hr
• Water saving: 50–70%
• WUE: Up to 90%

Suitable Crops & Areas:

• Orchards (mango, citrus, banana)
• Vegetables
• Greenhouses & polyhouses
• Undulating, saline, and water-scarce soils

Advantages:

• Maximum water and fertilizer saving (fertigation)
• Reduced weed growth
• Higher yield and quality
• No soil erosion
• Ideal for saline regions

Limitations:

• High initial cost
• Emitter clogging
• Requires filtration and skilled maintenance
• Not economical for dense crops like rice

Exam Points:

• Most efficient irrigation method
• Best suited for orchards and vegetables
• Promotes precision agriculture

Special Type: Typhoon System of Drip Irrigation

Description

• Modified drip system specially designed for sugarcane
• Uses high-discharge emitters
• Covers wider root spread

Advantages

• Suitable for long-duration crops
• Saves water and fertilizer
• Increases sugarcane yield
• Reduces lodging

Drainage

Definition: Drainage is the removal of excess surface or subsurface water to maintain favorable soil conditions for plant growth.

Types of Drainage

Surface Drainage

• Removal of surface water by open ditches.
• Simple and low-cost.
• Common in India.

1. Drainage of Flat Areas: Slope < 2%.
   b. Broad Bed and Furrow (BBF) System:

• Beds 120–150 cm wide, 15 cm high.
• Furrows 45 cm wide.
• Suitable for groundnut, pulses in heavy soils.
• 0.5% slope for easy drainage.

Subsurface Drainage

• Removes water below root zone to lower water table.

Methods:

Methods of Measuring Flow

Soil Moisture Constants & Matric Potential

Soil Moisture Potential

It is the energy status of soil water which determines its availability to plants.

Types of Soil Water Potential:

1. Matric Potential (Ψm): Due to adhesion and capillary forces. Always negative. Dominant in unsaturated soil.
2. Osmotic Potential (Ψo): Due to dissolved salts in soil water. Affects water uptake under saline conditions.
3. Gravitational Potential (Ψg): Due to gravity; affects drainage.
4. Pressure Potential (Ψp): Positive in saturated soil or turgid cells.

🌾 Soil Moisture Constants

Key Competitive Points

• Matric potential is negative in unsaturated soil.
• Soil moisture at saturation = 0 bar.
• Plant available water = FC – PWP.
• Field capacity attained 2–3 days after irrigation/rain.
• Wilting coefficient (PWP) determined using sunflower test.
• Soil moisture units: 1 bar = 10⁶ dynes/cm² = 1023 cm of water.
• Tensiometers measure soil moisture up to 0.85 bar tension.