IRRIGATION IN INDIA

by
P.V. Dehadrai
DIII/3403, Vasant Kunj, New Delhi-110070, India

Abstract

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. For soil and water conservation on agricultural lands, both agronomic and mechanical measures are deployed, such as contour farming, management of soil fertility, water nutrient interrelationship, balanced IPNS system and micronutrients. The paper gives details on irrigation water management for major crops in India: rice, wheat, maize, pulses, pigeon pea, gram, mung bean, black gram, field peas, lentil, oil seed crops, sugar cane and cotton. Irrigation is implemented through various methods such as border irrigation, basin irrigation, sprinklers and drip irrigation.

1. Introduction

Water is the most critical input for enhancing agricultural productivity, and therefore expansion of irrigation has been a key strategy in the development of agriculture in the country. The ultimate irrigation potential of India has been estimated to be 139.5 mha, comprising 58.5 mha from major and medium schemes, 15 mha from minor irrigation schemes and 66 mha from groundwater exploitation. India’s irrigation potential has increased from 22.6 mha in 1951 to about 90 mha at the end of 1995. It is estimated that even after achieving the full irrigation potential, nearly 50 percent of the total cultivated area will remain rain fed.

If we analyse agricultural growth during the past four decades, we find that high-yielding varieties, irrigated area expansion and fertilizer use have been the major factors contributing to the achievement of green revolution in India. The present level of consumption of total nutrients (NPK) is 14.3 million tonnes/year. On an all-India basis, per-hectare consumption of fertilizer (NPK), which was a meagre 2.0 kg/ha during the early sixties, has risen tremendously during the last 35 years or so, to a level of 76.5 kg/ha.

The share of water use other than for agriculture was only 13 percent in 1985, which is likely to become 27 percent by 2025. Such a fast growth of water need in the face of emerging supply constraints is likely to result in a wide supply gap for irrigation water in the near future.

2. 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 and 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. Catchment area and water resource potential of these basins is given in Table 1.

The total surface water resources of the country (yearly average flow rate) are about 1 869 km³. It has been estimated that due to extreme variability in precipitation, which disallows assured storage of all flash and peak flows, and due to non-availability of suitable storage sites in hills and plains, only about 690 km³ water is available for different uses. It is further estimated that about 360 km³ of groundwater would be available for irrigation. Thus a total of 1 050 km³ of utilizable surface and groundwater is available for irrigation. The projected budget of water for the twenty-first century is shown in Table 2.

2.1 Waterbodies and storages

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 waterbodies lie in the states of Kerala and Tamil Nadu, whereas Orissa, West Bengal and Kerala have the largest areas of brackish water (Table 3). 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 waterbodies. Today water storages hold 174 km³ of water, and another 72 km³ of the storage capacity will become available after the completion of the ongoing projects. Another 132 km³ of storage capacity is likely to be available from projects under consideration, making a total storage of 378 km³ as compared with the total water resources, including groundwater, available for irrigation, of 2 229 km³ in the country. Additional storage is available in the basins of Ganges, Krishna, Godavari, Narmada, Mahanadi, Brahmaputra and Barak, where the already existing live storage is also high. Tapi basin is leading in terms of storage capacity.

Table 1
Catchments area, average surface and groundwater potential in individual river basins,
India, 1998 (million m³ = Mm³)

Table 2
Freshwater use for various purposes in India (million ha-meters)

2.2 Groundwater resources

The total replenishable groundwater potential is considered to be 431.4 km³ per year. After making provisions for drinking and industrial water supply and for other purposes (other than irrigation), which is about 15 percent of the total potential, the potential available for irrigation is 360 km³ per year.

Table 3
Inland water resources (x10⁵ ha) of various types (1993) by state

There has been a steady increase in the irrigation potential from groundwater the use of which has gone up from 6.5 mha in 1951 to 35.38 mha in 1992. The contribution of groundwater to total food grain production of the country is significant, as more than 50 percent of the irrigated area is using groundwater and in several districts it is more than 80 percent.

Overexploitation of groundwater resources has caused continuous decline in water level, decline of well yields, drying of shallow wells, deterioration of groundwater quality, seawater intrusion into coastal aquifers and increase in cost of energy required to lift water from a greater depth.

The underground aquifers are supplemented from sources other than rainfall, such as seepage from canals and field channels, ponds, tanks, influent drainage from rivers and deep percolation from irrigated fields. In most of the canal-irrigated areas of the country, a substantial component of the water applied to fields percolates below the root zone and contributes to the groundwater potential. Based on the total length of main canals and distributaries, the total possible recharge in India due to canal seepage in estimated to be 5.463 mha-metres per year.

Conjunctive use of the surface and groundwater is being practised in India to a limited extent. The practice has been prevalent in the Cauvery delta in Tamil Nadu, the Godavari Pravara Canal system in Maharashtra, the Ganga and the Western Jamuna Canal in Haryana and in parts of Punjab and Uttar Pradesh.

In Israel and USA, saline groundwater has been used for irrigation to a limited extent after diluting it with good quality surface water. There is scope for adopting such practices in certain areas of Gujarat and Rajasthan where the groundwater is brackish.

2.3 Present water use

By 1994 utilization of water (surface and groundwater) was about 606 billion m³, leaving 536 billion m³ as unutilized. Of this, the use for irrigation, domestic and industrial purposes and for hydropower production and other purposes was 501.0, 30.4, 20.0, 34.0 and 20.0 billion m³, respectively. Statewise net irrigated area according to sources is given in Table 4.

The pre-eminent role of water in the environment is well reflected in the India’s National Water Policy, adopted in 1987, which emphasizes that the preservation of the quality of the environment and the ecological balance should be a primary consideration for the sustainable development of water resources. Since 1978, techno-economic appraisal of water resource projects in India includes an assessment of environmental impact. Due to a monsoonal climate about 40 mha of the land in India is prone to floods.

2.4 Farming practices

Both agronomic (contour farming, mulching, tillage, strip cropping and mixed cropping) and mechanical measures (contour bunding, graded bunding, bench terracing on steep slopes) are deployed, depending upon soil and climate. A simple practice of farming operations, viz. ploughing, cultivation and planning across the slope at the same elevation, is called contour farming. The ridges and furrows and the rows of the plants placed across the slope form a series of innumerable miniature reservoirs and barriers to the water moving over the land surface, reducing run-off, soil erosion and loss of plant nutrients.

Maintenance of optimum soil fertility using fertilizers has been receiving great attention, which is evident from the increase in fertilizer inputs from nearly 0.07 million tonnes in 1950 to 14.4 million tonnes in 1996-97. This has greatly contributed towards increasing the crop production.

Table 4
Statewise net area irrigated (thousand hectares) according to sources, 1992-93 (provisional)

2.5 Water management for individual crops

Rice

It is estimated that out of 42.8 mha area cultivated under rice in the country, about 6.8 mha are rainfed uplands, 21 mha are irrigated medium lands, and 15 mha are rainfed lowlands, where water depth varies from 5 cm to more than 100 cm under natural conditions. The storage of rain water in rice fields enhances its utilization in crop production, and induces groundwater recharge.

One of the objectives of storing rain water in rice fields is to minimize irrigation water application. In an experiment, irrigation was applied after one day of disappearance of ponded water. Under such a water regime, four irrigations were required to the rice crop grown in the plots having 6 cm bund height, three irrigations to 10 and 14 cm bund heights, and two irrigations to plots having 18, 22 and 30 cm bund heights.

Wheat

The Indo-Gangetic plains, comprising the states of Uttar Pradesh, Punjab, Haryana, Rajasthan, Madhya Pradesh and Bihar, form the most important wheat-growing areas. During 47 years wheat production increased about 11-fold, from 6.39 million tonnes in 1949-50 to 69.27 million tonnes in 1996-97. During the same period the area increased from 9.8 mha to 25.93 mha and yield from 655 kg/ha to 2 671 kg/ha.

About 85.2 percent of the total wheat sown is irrigated (1994-95). Wheat is grown largely under irrigation in most of the states. Efficient management of water seems to hold the key, since the use of fertilizers and other inputs is largely linked with it.

Maize

Maize is one of the important crops of India. The area under maize cultivation remained almost the same since 1968-69 (5.72 mha) to 1996-97 (6.25 mha). However, the production has increased by 85 percent, i.e. from 5.70 million tonnes in 1968-69 (yield 0.997 tonnes/ha) to 10.61 million tonnes (yield 1.698 tonnes/ha) in 1996-97. This has been achieved by extensive use of improved technologies, comprising high-yielding varieties, fertilizers, and irrigation. The irrigated area under maize has increased from about 0.41 mha in 1949-50 to 1.259 mha in 1994-95 (20.5 percent of total area).

Pulses

Pulses form a major part of food and a source of protein for a large section of the vegetarian population of the country. Pulses are mostly grown on marginal lands under rainfed conditions and are considered as poor farmers crop. In 1994-95, only 12.7 percent of the total area under pulse production (23.0 mha) was irrigated.

Pigeon pea (arhar)

The results of experiments involving irrigation at critical growth stages have shown that the main kharif crop responded to up to two irrigations (6-7 cm each) at pre-flowering/flowering and pod-development stages. However, under limited availability of irrigation water, one irrigation could be provided either at flowering stage, which enhances the yield by 0.40 tonnes/ha over the rainfed treatment (0.42 tonnes/ha) at Morena, or at pod-development stage for which a 14 percent increase in yield over rainfed treatment (1.42 tonnes/ha) was recorded at Faizabad.

Gram

Gram has been found to respond to irrigation at branching, flowering and pod-formation stages at Nafasari where it yielded 2.01 tonnes/ha, which is superior to two irrigations provided at any two stages (1.62 to 1.72 tonnes/ha). One irrigation applied at pod-formation stage yielded 9.5 percent more than the watering at branching (2.01 tonnes/ha) at Delhi, whereas at Kota the flowering stage was found more responsive to irrigation which yielded 19.3 percent more than watering at branching (2.02 tonnes/ha).

Mung bean

Mung bean is one of the important kharif season pulse crop of India. At Jammu two irrigations (6 cm each) applied at presowing and 20 days after sowing were found optimal for higher yield (1.56 tonnes/ha) during summer.

Black gram (urd)

Black gram is a highly prized pulse, rich in phosphoric acid. Its annual production in the country is about 1 million tonnes from about 2.5 mha area. A study conducted at Bhavanisagar in sandy loam soils has shown that the optimum value of IW/CPE was 0.6 for kharif season crop, involving 8 irrigations (4 cm each) besides a presowing irrigation (6 cm) to ensure proper germination, which yielded 1.08 tonnes/ha.

Field peas

The crop is grown in Uttar Pradesh, Punjab, Haryana, Madhya Pradesh, Jammu and Kashmir, Bihar, Delhi, Maharashtra, West Bengal, northeastern Himalaya states and Tamil Nadu. If winter rains are insufficient it needs one or two irrigations at appropriate growth stages. One irrigation at flowering gave optimum yield of 1.75 tonnes/ha at Pantnagar. Similarly, at Kota one irrigation at either flowering or pod-formation stage produced 2.39 tonnes/ha yield which was superior to one irrigation applied at branching that yielded 2.01 tonnes/ha.

Lentil (masoor)

Lentil is an important crop of the winter season and is grown throughout the northern and eastern regions. It is mainly grown on low-lying marginal lands that are subject to inundation. Lentil is normally cultivated as a rainfed crop, but it responds favourably to one or two irrigations depending upon rainfall and initial soil moisture storage in the profile.

Oil seed crops

Oil seeds, though energy-rich crops, are grown under energy starved conditions. The area under all the oil seed crops has increased by 2.5 fold between 1950-51 (10.7 mha) and 1996-97 (26.8 mha); at the same time the production has increased from 5.16 million tonnes to 25.0 million tonnes, which is nearly 5 fold. The increased productivity (0.48 tonnes/ha to 0.80 tonnes/ha) during the period is attributed to the use of improved varieties and management practices, including better use of irrigation water and fertilizers. Ground nut, rapeseeds and mustard, sesame, coconut, linseed, sunflower and soybean are the major oil seed crops grown in India.

Sugar cane

Sugar cane is the major source of sugar in the country. It is an important tropical crop, whose cultivated area has grown about 2.4 fold from 1.71 mha in 1950-51 to 4.17 mha in 1996-97. During the same period the area under irrigated cane has expanded from 67.3 percent to 87.9 percent, thus registering a 2.7-fold increase. Increased irrigated cane area in conjunction with other improved production technologies have steadily boosted the production from 57 million tonnes to 277 million tonnes.

Cotton

Cotton is one of the most important commercial fibre crops playing a key role in the economic and social affairs of the country. India ranks first in the world in respect of area under cotton and fourth in its production. The area under its production has expanded from 7 mha during 1953-54 to 9.12 mha during 1996-97. The production has increased from 4.13 million bales (of 170 kg each) to 14.25 million bales during the same period. The irrigated cotton area has also gone up from 10 percent in 1955-56 to 34.2 percent in 1994-95, which, together with other improved production technologies, has contributed to the increase in production.

Water requirements of crops vary with the crop and its variety, soil condition, fertilizer schedule and climate. Table 5 presents the rate of peak consumptive use expected under different climatic conditions.

Table 5
Maximum rates of soil moisture use by crops under different climatic conditions

2.6 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. Irrigation water may be applied to the crops by spreading it in a sheet or in small streams on the soil surface, by spraying it over the crop through pipes and nozzles or by applying it in drops to wet the crop root zone.

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.

Future gains in agricultural productivity of the country shall be critically determined by proper development and utilization of its surface and groundwater resources. Technological developments in pump manufacturing and deep well drilling have made groundwater extraction a common phenomenon, and the last three decades have witnessed a substantial increase in the groundwater development and utilization. Presently, groundwater is used to irrigate almost 50 percent of the total irrigated land in the country through about 5.5 million tubewells and more than 10 million dug wells. Unfortunately, these advantages have led to overexploitation and unsustainable utilization of this precious natural resource.

2.7 Management of poor quality water

Selection of crops, their varieties and salt tolerance at various stages of their growth are also important. Detailed guidelines for using saline irrigation water in India are available.

In the extreme cases of waterlogging and salinity, the seeds may not germinate and the plants may wilt permanently. Waterlogging and salinity of agricultural lands are due to a natural process or man-made activities. In irrigated areas, chemical degradation of land is a subsequent development on account of long duration waterlogging. Besides the erratic rainfall distribution, inundation of coastal areas by back-water flow from the sea and absence of proper soil and water-conservation measures in the catchments are also important factors leading to drainage congestion and related problems in the agricultural lands.

There is a lack of up-to-date and methodically monitored information on the type, severity and extent of drainage problems in the country. Estimates of waterlogged areas in India range from 2.5 to 16 mha, and those for salinized areas from 3.3 to 10.9 mha.

Beyond the above gross estimates for the whole country, very few published records based on rigorous monitoring exist on the progressive development of waterlogging and salinity in India.

2.8 Management of rain water resources

The technologies of rain water management are highly location-specific and are determined by physiographic, environmental, technical and socio-economic reasons. The main features are to conserve rain water where it falls, i.e. in the soil profile up to its maximum capacity and in storage structures for crop irrigation at a later stage. The technologies practised are (i) in situ water conservation, (ii) supplemental irrigation by run-off recycling, (iii) watershed management including agriculture, (iv) pond culture adjunct to canal system, (v) construction of high tidal-dykes, (vi) rice-fish integrated farming, (vii) using pressurized irrigation system, (viii) groundwater management, (ix) flood water management, (x) management of drainage and water-logging. Needless to say, ultimately the approaches have to be compatible with socio-economic adjustments of the target population.