Unit 1: Irrigation Management in Vegetable Crops

Introduction

Vegetable crops require frequent irrigation for better growth and development. Irrigation requirement may vary from crop to crop. If water is the limiting factor, then proper management and conservation practices can be fruitful to grow vegetables round the year. Conservation, management and use of irrigation water are critical to successful vegetable production, especially when the fields are under drought condition.

Leafy vegetables require frequent irrigation. Fruiting vegetables and root and tuber vegetables have different critical stages of water requirement.

Role of Water in Plants

Water is an essential element for plants.
It helps in the growth and development of plants.
It helps plants to absorb and transport minerals from soil.
It is essential for the conduct of biochemical reactions and integral for making food through photosynthesis.
It helps plants to manage heat or frost stresses.
It is necessary for seed germination and seedling establishment.

Sources of Water for Plants

Rainfall and irrigation are the two main sources of water for plants. Rainfall is a natural source, but it is limited and unpredictable. Irrigation is the practice of planning and applying water artificially to maintain soil moisture.

            The irrigation requirement depends on:
            Type of vegetable crop: Shallow-rooted crops need light but frequent irrigation
                    compared to deep-rooted crops.
Growing season: Summer crops need more frequent irrigation than winter crops.
Climate: Crops should be irrigated less frequently during cool climate and more
                    frequently in tropical/hot climate.
Soil type: Frequent but light irrigation for sandy soil; deep but less frequent for
                    clayey soil.
Irrigation system: Regular irrigation in drip systems; less frequent in
                    surface/sprinkler systems.

        

Session 1: Irrigation and Water Quality

Importance of Irrigation

Since vegetable crops contain 80-90% water they require a large amount of water.
Irrigation reduces dependence on rainfall.
Proper scheduling saves water and minimizes weed problems.
It helps in growing more crops in a year in the same field.

Sources of Irrigation Water

1. Surface Water Sources: Found on the land surface (Rivers, Ponds, Lakes, Dams). Generally good quality.

2. Groundwater Sources: Underground water lifted through dug wells, tube wells, and bore wells. Quality varies.

[Fig. 1.1: Sources of irrigation water - Diagram showing Surface Sources (Rivers, Ponds, Lakes, Dams) and Groundwater Sources (Dug wells, Tubewells/Borewell)]

Criteria of Suitable Water for Irrigation

Poor quality water can deteriorate soil health, deposit excess salt, reduce mineral uptake, and show toxicity .

pH of water: Should range between 6.5 to 8.5.
Water Salinity (EC): Measured by electrical conductivity. Water having EC below 1500 micromhos/cm is good .
Sodium Adsorption Ratio (SAR): Should be below 10. High sodium seals soil pores .
Residual Sodium Carbonate (RSC): Below 1.5 mg/litre is safe.
Boron: Below 1.0 ppm boron content is acceptable.

Quality Testing Instruments

pH Meter: Measures pH level. Ideally, soil/water pH should be 6-6.5. Must be calibrated.
Electrical Conductivity (EC) Meter: Measures total dissolved salts. Reports in dS/m or µS/cm.

[Fig 1.2: pH colour strip scale]
[Fig 1.3: Digital pH meter]
[Fig 1.4: Digital Electrical Conductivity (EC) meter]

Practical Exercises: Water Quality Testing

Activity 1: Collection of water samples

Procedure:

Tubewell/Handpump: Run for 15-20 mins to avoid 'pipe effect' before collecting. Collect directly into the bottle.
Ponds/Tanks: Take sample 5-10 meters inside the boundary to avoid boundary effect. Displace surface water and take from intermediate depth.
Label the sample with name, source, and date. Submit to lab within 2-3 days.

Activity 2: Measuring pH

Using Litmus/pH Paper: Dip paper in sample, observe colour change, match with colour strip .
Using pH Meter: Calibrate with pH 7 buffer. Insert electrode, stabilize for 20-30 seconds, record reading .

Check Your Progress

Fill in the blanks:

Water is an essential ________ for life.
Vegetable crops grow fast, hence they require ________ and ________.

Multiple Choice:

Irrigation is a practice of: (a) only artificial application of water.
Irrigation water suitable for most crops contains boron: (a) below 1.0 ppm.
Total dissolved salt in water is measured with a: (d) EC meter.
Electrical conductivity in irrigation water should be: (a) below 1500 micromhos/cm.

Session 2: Water Requirement and Irrigation Methods

Water Requirement (WR)

WR is the total quantity of water needed for crop growth and yield.

Formula: WR = Evapo-transpiration (ET) + Application losses + Special needs.

            Sample Water Requirements (mm):
            Tomato: 600-800
Chili: 450-500
Brinjal: 1000
Potato: 500-700
Onion: 640-700

        

Table 1.1: Rooting depth of various vegetable crops

Rooting depth category	Vegetable crops	Root depth
Shallow rooted	Onion, cabbage, cauliflower, celery, potato, radish, cowpea, lettuce, broccoli	45-60 cm
Moderately deep-rooted	Beans, beetroot, turnip, cucumber, brinjal, chili, sweet pepper, muskmelon, tomato	90-120 cm
Deep-rooted	Asparagus, pumpkin, winter squash, sweet potato, watermelon	More than 120 cm

Critical Stages of Water Requirement

Water stress at critical stages can adversely affect growth and yield .

Table 1.2: Critical stages of vegetable crops

Crop	Critical Stages
Tomato, chili, brinjal	Flowering, fruit set and fruit development
Potato	Tuber initiation and tuber development
Onion, garlic	Bulb formation and enlargement
Cabbage, cauliflower	Head formation and enlargement
Leafy vegetables	Entire crop duration

Methods of Irrigation

The principal systems are surface, sub-surface, sprinkler, and drip irrigation.

[Fig. 1.5: Irrigation systems and methods chart]

1. Surface Irrigation System

Most common and cheapest method (gravity irrigation).

Flood Irrigation: Water flows freely like a sheet. Used for onion, garlic, pea, spinach. Disadvantage: Maximum water loss, increases weed population.
Border Irrigation: Land divided into strips with borders. Suitable for crops on steep slopes.
Check Basin Irrigation: Field divided into square/rectangular plots. Good for leaching salts. A modification is the Ring and Basin method used for fruit trees or vine vegetables like bitter gourd .
Furrow Irrigation: Water moved in furrows between ridges. Common for tomato, brinjal, potato. Advantages: High water efficiency, less weeds.

[Fig. 1.6: Flood irrigation method]
[Fig. 1.7: Border irrigation method]
[Fig. 1.8: Check basin irrigation method]
[Fig. 1.10: Furrow irrigation method]

2. Sub-surface Irrigation

Application of water below ground surface using capillaries. Uses perforated pipes underground.

Advantage: Reduces evaporation. Disadvantage: High installation cost, difficult to locate leaks.

3. Sprinkler or Overhead Irrigation

Water is sprinkled over the crop like rain using nozzles. Ideal for hilly and undulating regions.

Advantages: Water saving 30-35%, protects from frost, suitable for undulating land.
Disadvantages: High cost, affected by wind velocity.

4. Drip Irrigation System

Also known as trickle or micro irrigation. Supplies water drop by drop to the root zone. Saves 40-60% water.

Components: Pump, Filter, Main line, Lateral lines, Emitters (drippers) .

Advantages: 80-90% water use efficiency, increases yield 10-25%, suitable for water scarce areas .
Disadvantages: High installation cost, needs technical skill.

[Fig. 1.12: Components of a drip irrigation system]
[Fig. 1.13: Component and layout of a drip irrigation system]

Practical Exercises (Session 2)

Activity 1: Identify components of drip irrigation system.

Activity 2: Demonstrate the border irrigation method.

Check Your Progress (Session 2)