Irrigation

1. Agricultural importance and basic concepts

India receives much of its annual rainfall during the southwest monsoon, but its onset, withdrawal and within-season distribution vary. Irrigation bridges dry spells during kharif, supplies water for rabi crops and permits summer cultivation where water is available. Even relatively wet regions need supplemental irrigation when rainfall does not coincide with critical crop stages. Thus, annual rainfall totals alone do not determine irrigation requirements.

Reliable irrigation enables multiple cropping, adoption of high-yielding varieties and more effective use of fertilisers. It helped sustain the Green Revolution, particularly the rice–wheat system of northwestern India. Nevertheless, assured water can encourage unsuitable crop choices. Water-intensive paddy and sugarcane in water-stressed regions illustrate the importance of matching crops to agroclimatic conditions rather than treating irrigation expansion as an unconditional benefit.

Net irrigated area measures the physical area irrigated at least once during a year. Gross irrigated area includes repeated irrigation of the same land under successive crops. Irrigation intensity is gross irrigated area divided by net irrigated area, multiplied by 100. Culturable command area is the cultivable part of the area that an irrigation system can serve; it is not necessarily the area actually irrigated.

2. Sources and their geographical distribution

Canal irrigation is favoured by extensive plains, relatively gentle slopes and dependable river supplies. Diversion structures or storage reservoirs feed networks of main canals, distributaries and field channels. The northern plains and several peninsular river deltas have important canal commands. Perennial canals receive regulated supplies, whereas traditional inundation canals depend on high river stages and are less dependable.

Wells and tube wells provide decentralised irrigation that farmers can schedule according to crop needs. Thick alluvial aquifers and productive groundwater reserves explain their prominence in the Indo-Gangetic plains. Dug wells also occur widely in peninsular India, but groundwater there is often stored in weathered and fractured hard rock. Well yields can consequently vary sharply over short distances, and deeper drilling does not guarantee a dependable supply.

Tanks store local runoff behind embankments and are especially characteristic of peninsular landscapes, including Tamil Nadu, Karnataka and Telangana. Undulating terrain, natural depressions and seasonal streams favour these systems. Tanks may support irrigation, livestock, fisheries and groundwater recharge. Encroachment, siltation and disrupted feeder channels reduce their usefulness. Lift irrigation, meanwhile, raises water from rivers, reservoirs or other sources to higher ground and requires energy for pumping.

3. Application methods and water-use efficiency

Surface irrigation distributes water over fields through flooding, basins, borders or furrows. It is generally inexpensive to establish, but poor land levelling and uncontrolled flows can cause uneven watering, runoff and deep percolation. Furrows are suitable for many row crops because water moves along channels between crop rows. Laser land levelling can improve uniformity and reduce unnecessary application, especially in irrigated plains.

Sprinkler irrigation applies pressurised water as artificial rainfall. It is useful on undulating land and light-textured soils where conventional surface irrigation may be difficult. However, wind can distort distribution, evaporation can increase losses, and pressure requirements create energy costs. Water quality also matters because saline water sprayed on leaves can damage sensitive crops.

Drip irrigation supplies frequent, small quantities near the root zone through emitters. It is particularly useful for orchards, vegetables and widely spaced crops. Fertigation introduces soluble fertilisers through the irrigation system. Benefits depend on proper design, filtration, maintenance and scheduling; clogged emitters and unsuitable operating pressure reduce performance. Micro-irrigation therefore requires continuing technical support rather than equipment installation alone.

Higher field-level efficiency does not automatically produce equivalent basin-level water savings. Some seepage and percolation return to aquifers or downstream channels. Farmers may also use water saved per hectare to expand irrigation. Sustainable assessment must therefore consider consumptive use, return flows and crop area, while recognising that seepage can be harmful where it causes waterlogging or mobilises salts.

4. Environmental stresses and management responses

Groundwater depletion occurs when abstraction persistently exceeds replenishment. Intensive pumping for irrigation, encouraged in some areas by subsidised electricity and water-intensive crop incentives, has lowered groundwater levels in parts of Punjab, Haryana, Rajasthan and other states. Consequences include rising pumping costs, drying shallow wells and unequal access: farmers able to finance deeper borewells may outcompete poorer users.

Waterlogging develops when the water table rises sufficiently to restrict aeration in the crop root zone. Canal seepage, excessive irrigation and inadequate drainage can contribute. In arid and semi-arid commands, capillary movement brings dissolved salts towards the surface, where evaporation concentrates them. Salinity impairs crop water uptake; sodicity involves excessive exchangeable sodium and can damage soil structure. The two problems require diagnosis rather than identical treatment.

Responses include surface and subsurface drainage, suitable leaching where drainage permits, conjunctive use of surface water and groundwater, and crop diversification. Gypsum can reclaim sodic soils under appropriate conditions, but it is not a universal remedy for all salt-affected land. Irrigation scheduling should consider soil moisture, crop growth stage and weather. At the command scale, equitable deliveries to tail-end farmers and maintenance of distributaries are as important as new storage construction.

5. Institutions, schemes and examination linkages

Water is primarily a State List subject under Entry 17, subject to Union powers concerning interstate rivers and river valleys under Entry 56. Irrigation development therefore involves state departments, central assistance and interstate coordination. Water User Associations can support participatory irrigation management through local distribution, maintenance and conflict resolution, although their effectiveness depends on genuine authority, finance and inclusive representation.

Pradhan Mantri Krishi Sinchayee Yojana, launched in 2015, seeks to improve irrigation access and water-use efficiency. Its architecture has included the Accelerated Irrigation Benefits Programme, Har Khet Ko Pani, watershed development and Per Drop More Crop. From 2022–23, Per Drop More Crop has been implemented under Rashtriya Krishi Vikas Yojana. Scheme names should therefore be read with their administrative period rather than assumed to have an unchanged structure.

Atal Bhujal Yojana promotes community-led sustainable groundwater management in selected water-stressed areas of seven states. The Central Ground Water Board assesses groundwater resources, while the Central Water Commission performs major surface-water planning and technical functions. For Prelims, connect irrigation with aquifer geology, river basins, cropping seasons, soil degradation and energy use. Distinguish irrigation potential created from potential utilised: unfinished field channels, poor maintenance and unreliable supplies can leave infrastructure underused.

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