Since independence India has invested numerous resources on irrigation, both public (canal irrigation) and private (tube wells).
The consolidation of ongoing irrigation schemes – the Accelerated Irrigation Benefit Programme (AIBP), Integrated Watershed Management Programme (IWMP) and On Farm Water Management (OFWM) – into the Prime Minister’s Krishi Sinchayi Yojana (PMKSY) offers the possibility of convergence of investments in irrigation, from water source to distribution and end-use.
India has many rivers whose total catchment area is estimated to be 252.8 million ha (mha).
Out of about 1,869 km3 of surface water resources, about 690 km3 of water is available for different uses.
The ultimate irrigation potential of the country has been estimated to be 139.5 mha.
India has acquired an irrigation potential of about 84.9 mha against the ultimate irrigation potential.
About 360 km3 of groundwater is also available for irrigation.
Irrigation is implemented through various methods such as border irrigation, basin irrigation, sprinklers and drip irrigation.
It is estimated that even after achieving the full irrigation potential, nearly 50 percent of the total cultivated area will remain rain fed.
Water resources of India
The annual precipitation including snowfall, which is the main source of water in India, is estimated to be in the order of 4,000 km3.
The annual potential evapo-transpiration in the country is 1,775 mm, but it varies from a minimum of 1,239 mm in Jammu & Kashmir to a maximum of 2,052 mm in Andhra Pradesh.
The total catchment area of Indian rivers is estimated to be 252.8 mha.
The Ministry of Water Resources, Government of India, for the purpose of efficient water management has divided the whole country into 20 river basins, comprising the major basins and including all the other remaining medium and small river systems.
Water bodies and storage
Inland water resources of India are classified as rivers, canals, reservoirs, tanks and ponds, beels, oxbows, lakes, derelict water and brackish water, and they cover an area of 7 mha excluding rivers and canals.
Uttar Pradesh has the highest total length of rivers and canals of 31,200 km, followed by Jammu & Kashmir and Madhya Pradesh.
The total length of navigable waterways in the country is estimated to be 15,783 km, and 83 percent of this is in 10 important rivers of the country.
Most tanks and ponds (2.3 mha) are present in the southern states of Andhra Pradesh, Karnataka and Tamil Nadu.
The states Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh, Orissa, Maharashtra, Rajasthan and Uttar Pradesh account for large reservoirs with a total water surface area of 2.1 mha.
Most of the lakes, beels and derelict water-bodies lie in the states of Kerala and Tamil Nadu, whereas Orissa, West Bengal and Kerala have the largest areas of brackish water.
Overall, the inland water resources are unevenly distributed in the country, and five states, i.e. Orissa, Tamil Nadu, Andhra Pradesh, Karnataka and West Bengal, account for more than 50 percent of the inland water-bodies.
Methods of irrigation
Efficient methods of irrigation enable the application of the right amount of water to the crop at the right time and its uniform distribution in the field.
 Border irrigation
Border irrigation is a controlled surface flooding method of water application.
The field is divided into a number of long parallel strips called borders that are separated by low ridges.
The width of a border usually varies from 3 to 15 m. The length of a border varies from 60 to 120 m in sandy and sandy loam soil, 100 to 180 m in medium loam soils and 150 to 300 m in clay loam or clay soils.
The border method of irrigation is most suitable for close growing grain crops, such as wheat, barley and fodder crops.
Field trials in India have shown that border irrigation is suitable in most areas of the country. Water is retained in the basin until it soaks into the soil.
 Basin irrigation
The basin method of irrigation is essentially the check basin method applied to orchards.
In flat lands, the basins are square, while on sloping lands the basins are formed by constructing ridges along adjacent contours with short cross ridges at either end.
Usually there is one tree to a basin.
 Sprinkler irrigation
In sprinkler irrigation, water is sprayed into the air through a sprinkler nozzle and allowed to fall on the land surface in a uniform pattern at a rate less than the infiltration rate of the soil.
Sprinklers were introduced in India during the early 1950s.
Initially, the sprinklers were used on high value plantation crops such as tea, coffee, chicory, cardamom and in orchards.
Their use is gaining popularity on food crops, orchards, cotton and vegetables in areas where sprinklers are economically justifiable and technically feasible.
Sprinkler irrigation can be used for almost all crops (except rice and jute) and on nearly all soils.
 Drip irrigation
Drip irrigation, also called trickle irrigation, involves slow application of water to the plant root zone.
The losses by deep percolation and evaporation are minimized.
A precise amount of water is applied to replenish the depleted soil moisture at frequent intervals, for optimum plant growth.
The system enables the application of water and fertilizer at an optimum rate to the plant root system.
The amount of water supplied to the soil is almost equal to the daily consumptive use, thus maintaining a low moisture tension in soil.