💧 Irrigation & Water Management
Irrigation and Water Management
Water is the single most critical input in agriculture after land itself. India's food security depends on how efficiently we manage water — from sourcing and delivery to scheduling and conservation. This lesson covers the complete spectrum of irrigation and water management for CUET Agriculture.
Importance of Irrigation in Indian Agriculture
India's relationship with irrigation is unique — the country has both the largest irrigated area globally and a massive dependence on unpredictable monsoon rainfall:
- India has the largest irrigated area in the world (approximately 72 million hectares net irrigated area)
- About 52% of India's cropped area is still rainfed (dependent on monsoon), making agriculture vulnerable to drought
- Irrigation contributes to more than 50% of food production from less than half the cropped area — demonstrating how dramatically irrigation multiplies productivity
- Irrigation stabilizes crop production year to year, enables multiple cropping (2-3 crops per year instead of one), and allows use of high-yielding varieties that require assured moisture
IMPORTANT
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Irrigation and Water Management
Water is the single most critical input in agriculture after land itself. India's food security depends on how efficiently we manage water — from sourcing and delivery to scheduling and conservation. This lesson covers the complete spectrum of irrigation and water management for CUET Agriculture.
Importance of Irrigation in Indian Agriculture
India's relationship with irrigation is unique — the country has both the largest irrigated area globally and a massive dependence on unpredictable monsoon rainfall:
- India has the largest irrigated area in the world (approximately 72 million hectares net irrigated area)
- About 52% of India's cropped area is still rainfed (dependent on monsoon), making agriculture vulnerable to drought
- Irrigation contributes to more than 50% of food production from less than half the cropped area — demonstrating how dramatically irrigation multiplies productivity
- Irrigation stabilizes crop production year to year, enables multiple cropping (2-3 crops per year instead of one), and allows use of high-yielding varieties that require assured moisture
IMPORTANT
The stark contrast — 48% of irrigated area producing >50% of food — highlights why expanding and improving irrigation efficiency is a top priority for Indian agriculture.
Sources of Irrigation in India
| Source | Share of Irrigated Area | Key Features |
|---|---|---|
| Tube wells | ~46% | Largest source; deep groundwater extraction using bore technology |
| Canals | ~24% | Government-managed; surface water from dams/rivers; major in Punjab, UP, Rajasthan |
| Wells | ~17% | Traditional; shallow groundwater accessed by open wells |
| Tanks | ~3% | Traditional water harvesting structures; prominent in South India (Tamil Nadu, AP) |
| Others | ~10% | Rivers, springs, lift irrigation, etc. |
WARNING
Groundwater accounts for over 60% of irrigation in India (tube wells + wells combined). Over-exploitation of groundwater is a major concern in Punjab, Haryana, Rajasthan, and Tamil Nadu, where water tables are declining rapidly. The shift from canal to groundwater irrigation has given farmers independence but created a sustainability crisis.
Types of Irrigation
1. Surface Irrigation (Gravity-Based)
The most common method globally (over 80% of irrigated area worldwide), surface irrigation uses gravity to distribute water across the field. It is the oldest and simplest approach but the least efficient.
| Method | Description | Suitable For | Water Use Efficiency |
|---|---|---|---|
| Flood/Basin irrigation | Entire field flooded with water | Rice, flat land crops | 30-40% |
| Furrow irrigation | Water flows through furrows (channels) between crop rows | Row crops: maize, cotton, sugarcane, vegetables | 40-50% |
| Border strip irrigation | Water flows down long narrow strips separated by bunds (earthen walls) | Close-growing crops: wheat, groundnut | 40-50% |
| Check basin irrigation | Small basins with bunds on all sides; each basin filled independently | Orchards, vegetable plots | 40-50% |
| Ring basin | Circular basins around tree trunks | Fruit trees | 40-50% |
Advantages: Low initial cost, simple technology, no energy needed (gravity does the work)
Disadvantages: Lowest efficiency (50-70% of water is wasted), uneven water distribution, waterlogging risk, high labour requirement
2. Sprinkler Irrigation
Water is sprayed into the air as artificial rain through nozzles under pressure. This mimics natural rainfall and provides more uniform coverage than surface methods.
Types of Sprinkler Systems:
- Portable — Can be moved from field to field (most flexible)
- Semi-permanent — Main line fixed, laterals portable
- Permanent — Entire system fixed in place
- Centre pivot — Rotates around a central point; covers large circular area (common in USA)
- Rain gun — High-pressure single nozzle; covers large area with one unit
| Feature | Details |
|---|---|
| Water use efficiency | 60-70% |
| Water saving | 30-40% compared to surface irrigation |
| Suitable for | Undulating terrain (where surface irrigation fails), sandy soils, closely-spaced crops |
| Not suitable for | Heavy clay soils (poor infiltration causes runoff), very windy areas (droplets blown away), tall crops (intercept spray) |
| Pressure required | 2-4 kg/cm² |
3. Drip (Micro/Trickle) Irrigation
Water is delivered drop by drop directly to the root zone through emitters/drippers attached to lateral pipes. This is the most water-efficient irrigation method available.
| Feature | Details |
|---|---|
| Water use efficiency | 80-95% (highest among all methods) |
| Water saving | 30-60% compared to surface irrigation |
| Fertigation | Fertilizer application through drip system — most efficient fertilizer delivery method |
| Suitable for | Orchards, vegetables, flowers, sugarcane, cotton, banana |
| Weed reduction | Significant — only root zone is wetted, so weeds between rows don't get water |
| Initial cost | High (Rs. 50,000-1,00,000/ha) but subsidized by government |
Components of a drip system: Pump/water source → Filter (sand/screen/disc) → Main line → Sub-main → Laterals → Emitters/drippers
Government subsidy: Up to 55-60% under PMKSY (Per Drop More Crop component)
Why is drip irrigation not used everywhere if it's so efficient?
Despite its high efficiency, drip irrigation has limitations: (1) **High initial cost** even with subsidies, (2) **Clogging** of emitters by sediment, salts, or algae requires regular maintenance, (3) **Not suitable for closely-spaced crops** like wheat or rice that cover the entire field, (4) **Salt accumulation** at the edges of the wetted zone in arid areas, (5) Requires **pressurized water supply** and technical knowledge. It is most cost-effective for high-value crops (fruits, vegetables, flowers) where the water savings and yield increase justify the investment.Comparison of Irrigation Methods
This comparison table is frequently tested in CUET:
| Parameter | Surface | Sprinkler | Drip |
|---|---|---|---|
| Water use efficiency | 30-50% | 60-70% | 80-95% |
| Uniformity | Low | Medium-High | Very High |
| Initial cost | Low | Medium | High |
| Labour requirement | High | Low | Very Low |
| Fertigation | Not possible | Limited | Best suited |
| Weed problem | High | Medium | Low |
| Suitable terrain | Flat only | Undulating | Any terrain |
Water Requirement of Crops
Key Terms
Understanding these terms is essential for irrigation planning:
| Term | Definition |
|---|---|
| Duty of water | Area of land (hectares) that can be irrigated by 1 cumec (m³/s) of water during the crop period. Higher duty = more efficient use |
| Delta of water | Total depth of water (cm) required by a crop during its entire growing period. Think of it as the total "rainfall equivalent" the crop needs |
| Base period | Time from first irrigation to last irrigation of a crop |
| Consumptive use (ET) | Water used by plant through transpiration + evaporation from soil surface (also called evapotranspiration) |
| Crop water requirement | Total water needed = ET + application losses + conveyance losses |
NOTE
Duty and Delta are inversely related: Duty = 8.64 × Base period / Delta. A crop with a high delta (needs lots of water) has a low duty (less area can be irrigated per unit of water).
Water Requirement of Major Crops
| Crop | Water Requirement (mm) | Delta (cm) | Number of Irrigations |
|---|---|---|---|
| Rice (paddy) | 1200-1400 | 120-140 | Continuous submergence |
| Wheat | 350-450 | 35-45 | 4-6 |
| Maize | 500-600 | 50-60 | 6-8 |
| Sugarcane | 1500-2000 | 150-200 | 25-35 |
| Cotton | 500-700 | 50-70 | 6-8 |
| Groundnut | 400-500 | 40-50 | 4-6 |
| Mustard | 200-300 | 20-30 | 2-3 |
IMPORTANT
Rice and Sugarcane are the most water-demanding crops. Millets and Mustard are the most water-efficient crops. This knowledge drives policy decisions about which crops to promote in water-scarce regions.
Irrigation Scheduling
Irrigation scheduling answers the critical questions: When to irrigate and How much water to apply. Proper scheduling prevents both water stress (under-irrigation) and waterlogging (over-irrigation).
Methods of Scheduling
| Method | Basis | Description |
|---|---|---|
| Critical stage approach | Crop growth stage | Irrigate at moisture-sensitive (critical) stages — simplest and most practical approach |
| Soil moisture depletion | Available soil water | Irrigate when 50% of available water is depleted (for most crops) |
| IW/CPE ratio | Climatological data | Ratio of irrigation water depth to cumulative pan evaporation — scientific and widely recommended |
| Tensiometer | Soil moisture tension | Irrigate when soil tension reaches a set threshold (instrument-based) |
| Gravimetric method | Soil sampling | Direct measurement of soil moisture by weighing soil samples before and after oven drying |
Critical Stages of Irrigation for Major Crops
Missing irrigation at the critical stage causes disproportionately large yield losses. Each crop has specific growth stages when it is most sensitive to water stress:
| Crop | Critical Stages | Most Critical Stage |
|---|---|---|
| Rice | Tillering, Panicle initiation, Flowering, Grain filling | Flowering |
| Wheat | Crown Root Initiation (CRI), Tillering, Jointing, Flowering, Milk/Dough | CRI (21 DAS) |
| Maize | Tasseling, Silking, Grain filling | Tasseling-Silking |
| Mustard | Flowering, Pod formation | Flowering |
| Sugarcane | Germination, Tillering, Grand growth | Grand growth |
| Groundnut | Flowering, Pegging, Pod development | Pegging-Pod development |
| Chickpea | Flowering, Pod filling | Flowering |
| Soybean | Flowering, Pod development | Pod development |
IMPORTANT
CRI stage in wheat (21 days after sowing) is the single most critical irrigation — missing it can reduce yield by 30-40%. At CRI, the crown roots (which will become the primary root system) are developing. Without water at this stage, the secondary root system fails to establish, permanently stunting the plant.
IW/CPE Ratio Method
This is the most scientific field-level method for scheduling irrigation:
- IW = Depth of irrigation water applied (usually 5-6 cm per irrigation)
- CPE = Cumulative Pan Evaporation measured using USWB Class A Open Pan Evaporimeter
- IW/CPE of 0.8-1.0 recommended for most crops
- Higher ratio (1.0-1.2) for water-loving crops; lower (0.6-0.8) for drought-tolerant crops
IW/CPE calculation example
If IW = 6 cm and IW/CPE = 0.8, you irrigate when CPE reaches 6/0.8 = **7.5 cm**. This means you wait until the pan evaporimeter shows 7.5 cm of cumulative evaporation since the last irrigation, then apply 6 cm of irrigation water. If the pan shows 1 cm/day evaporation, you would irrigate every 7-8 days.Water Use Efficiency (WUE)
Definition
WUE = Crop yield (kg/ha) / Total water used (ha-cm or m³)
Also expressed as kg grain per mm of water or kg grain per ha-cm of water. Higher WUE means more "crop per drop."
Ways to Improve WUE
Each method addresses a different source of water loss:
| Method | Water Saving | Description |
|---|---|---|
| Drip irrigation | 30-60% | Directly to root zone; eliminates conveyance and distribution losses |
| Sprinkler irrigation | 30-40% | Reduced conveyance and distribution losses compared to surface |
| Mulching | 20-30% | Reduces evaporation from soil surface by covering it with straw/plastic |
| Laser land leveling | 20-25% | Ensures uniform water distribution across the field; prevents pooling in low spots |
| Raised bed planting | 25-30% | For wheat; furrow irrigation between beds instead of flooding entire field |
| System of Rice Intensification (SRI) | 30-50% | Alternate wetting and drying; no continuous flooding; wider spacing; young single seedlings |
| AWD (Alternate Wetting and Drying) | 15-30% | For rice; allows soil to dry between irrigations instead of continuous submergence |
| Canal lining | 20-30% | Reduces seepage losses during water conveyance from source to field |
| Deficit irrigation | Variable | Deliberately providing less water at non-critical stages to save water for critical stages |
| Crop residue management | 10-15% | Reduces evaporation; improves infiltration by protecting soil surface |
TIP
SRI (System of Rice Intensification) is revolutionary because rice is traditionally grown under continuous flooding (the most water-intensive method). SRI saves 30-50% water while often increasing yields by 20-30% through better root development and soil aeration.
Drainage
Definition
Drainage is the removal of excess water from the soil surface or root zone to create favourable conditions for crop growth. It is the counterpart to irrigation — while irrigation adds water, drainage removes it.
Types of Drainage
| Type | Method | Application |
|---|---|---|
| Surface drainage | Open ditches, land grading, field drains | Removal of water from soil surface (standing water) |
| Sub-surface drainage | Tile drains, perforated pipe drains, mole drains | Lowering of water table from below surface |
| Vertical drainage | Tube well pumping | Lowering water table by extracting groundwater (serves dual purpose: drainage + irrigation) |
| Bio-drainage | Deep-rooted trees (Eucalyptus, Poplar) | Transpiration-based water table control — trees pump water from deep soil and release it to atmosphere |
Importance of Drainage
Adequate drainage is essential for healthy crop growth:
- Prevents waterlogging and soil salinization (rising water table brings salts to surface)
- Improves soil aeration and root respiration (roots need oxygen)
- Removes toxic salts from root zone
- Essential in canal command areas (where seepage from canals raises water tables) and low-lying regions
- Prevents accumulation of CO₂ and harmful gases (H₂S, methane) in root zone
Waterlogging
Waterlogging occurs when the water table rises to within the root zone, saturating the soil and depriving roots of oxygen:
- Causes: Over-irrigation, seepage from canals, poor natural drainage, heavy rainfall
- Effects: Reduced aeration → root decay, nutrient unavailability (Fe/Mn toxicity), salt accumulation at surface
- About 8.5 million hectares in India are waterlogged — a significant loss of productive land
Irrigation Water Quality
Not all water is suitable for irrigation. Poor quality water can salinize or sodify the soil, causing permanent damage:
Key Parameters
| Parameter | Safe Limit | Significance |
|---|---|---|
| pH | 6.5-8.5 | Most crops tolerate this range |
| EC (Electrical Conductivity) | < 2 dS/m | Measures total dissolved salts; higher EC = more salts |
| SAR (Sodium Adsorption Ratio) | < 10 | High SAR causes soil sodicity (Na⁺ destroys soil structure) |
| RSC (Residual Sodium Carbonate) | < 1.25 meq/L | Safe for irrigation; high RSC precipitates Ca and Mg, increasing Na hazard |
| Boron | < 1 ppm | Toxic at higher levels for many crops |
| Chloride | < 4 meq/L | Safe for most crops |
USDA Water Classification
The USDA classifies irrigation water using a C-S system where C = salinity class and S = sodium hazard class:
| Class | EC (dS/m) | SAR | Suitability |
|---|---|---|---|
| C1-S1 | < 0.25 | < 10 | Excellent — suitable for all crops and soils |
| C2-S1 | 0.25-0.75 | < 10 | Good — suitable for most crops with moderate leaching |
| C3-S1 | 0.75-2.25 | < 10 | Medium — use only with good drainage; select salt-tolerant crops |
| C4 | > 2.25 | — | Poor — generally unsuitable for irrigation |
NOTE
SAR formula: SAR = Na⁺ / √((Ca²⁺ + Mg²⁺) / 2). An SAR > 10 indicates sodicity risk (Na will damage soil structure). An EC > 4 dS/m indicates salinity risk (excess salts will reduce crop growth through osmotic stress).
Watershed Management
Definition
Watershed management is the scientific management of land and water resources within a watershed (a geographical area that drains to a common point — a river, stream, or lake) for optimum production with minimum soil erosion. It takes a holistic, landscape-level approach rather than focusing on individual fields.
Techniques
| Category | Methods |
|---|---|
| Engineering measures | Contour bunding, graded bunding, bench terracing, check dams, nala bunding |
| Agronomic measures | Contour cultivation, strip cropping, mulching, cover cropping |
| Vegetative measures | Contour hedges (Vetiver grass is widely used), grass waterways, agroforestry |
| Water harvesting | Farm ponds, percolation tanks, recharge pits, rooftop harvesting |
Rainwater Harvesting
Capturing and storing rainwater for later use is increasingly important as groundwater depletes:
- Farm ponds: Store surface runoff water for supplemental irrigation during dry spells
- Percolation tanks: Allow collected water to recharge groundwater (water seeps down)
- Rooftop harvesting: Collecting rainwater from rooftops into storage tanks for domestic or agricultural use
- Johads: Traditional earthen check dams in Rajasthan — community-managed structures that recharge groundwater
- Tamil Nadu was the first state to mandate rainwater harvesting (2001)
Government Schemes Related to Irrigation
| Scheme | Year | Key Features |
|---|---|---|
| PMKSY (Pradhan Mantri Krishi Sinchayee Yojana) | 2015 | Motto: "Har Khet Ko Paani" + "Per Drop More Crop"; micro irrigation subsidy (55-60%) |
| AIBP (Accelerated Irrigation Benefit Programme) | 1996 | Fast-tracking incomplete major/medium irrigation projects |
| CADWM (Command Area Development) | 1974 | On-farm development works in canal command areas (field channels, land leveling) |
| Atal Bhujal Yojana | 2020 | Sustainable groundwater management in 7 over-exploited states |
| Jal Jeevan Mission | 2019 | Rural drinking water (not irrigation directly, but improves overall water management) |
Key Points for CUET
Quick Revision Checklist
- **Tube wells** are the largest source of irrigation in India (~46%) - Drip irrigation: **80-95% efficiency** (highest); Sprinkler: 60-70%; Surface: 30-50% - **CRI stage** in wheat is the most critical for irrigation (21 DAS) — 30-40% yield loss if missed - Rice and sugarcane are the most **water-demanding** crops - WUE = Yield / Water used - **PMKSY (2015):** "Har Khet Ko Paani" + "Per Drop More Crop" - **SAR > 10** = Sodicity risk; **EC > 4 dS/m** = Salinity risk - **Tamil Nadu**: First state to mandate rainwater harvesting (2001) - Laser land leveling saves 20-25% irrigation water - AWD and SRI in rice save 15-50% water compared to continuous flooding - **Duty** = Area irrigated per unit discharge; **Delta** = Total depth of water for a crop - India has about **8.5 million hectares** of waterlogged land - Groundwater accounts for >60% of irrigation — over-exploitation is a major concernSummary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| India's irrigated area | Largest in the world (~72 million ha); ~52% cropped area still rainfed |
| Largest irrigation source | Tube wells (~46%); groundwater = >60% of all irrigation |
| Surface irrigation efficiency | 30-50% (lowest); flood, furrow, border strip, check basin |
| Sprinkler efficiency | 60-70%; saves 30-40% water; not for heavy clay or windy areas |
| Drip efficiency | 80-95% (highest); saves 30-60%; best for fertigation; subsidy 55-60% under PMKSY |
| Duty of water | Area (ha) irrigated by 1 cumec; inversely related to Delta |
| Delta of water | Total depth of water (cm) for entire crop period |
| Rice water need | 1200-1400 mm (very high); continuous submergence |
| Sugarcane water need | 1500-2000 mm (highest) |
| Most water-efficient crops | Millets and Mustard |
| Wheat — Most critical stage | CRI at 21 DAS; missing = 30-40% yield loss |
| Maize — Most critical stage | Tasseling-Silking |
| IW/CPE ratio | 0.8-1.0 recommended; uses USWB Class A Open Pan |
| WUE formula | Yield (kg/ha) / Water used (ha-cm) |
| SRI | Young seedlings, single/hill, AWD; saves 30-50% water |
| Mulching | Reduces evaporation; saves 20-30% |
| Laser land leveling | Saves 20-25% water |
| Waterlogged area (India) | ~8.5 million hectares |
| EC safe limit | < 2 dS/m |
| SAR safe limit | < 10; high SAR → soil sodicity |
| Rainwater harvesting mandate | Tamil Nadu — first state (2001) |
| PMKSY | 2015; "Har Khet Ko Paani" + "Per Drop More Crop" |
| Atal Bhujal Yojana | 2020; groundwater management in 7 states |
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