What is Irrigation
Water needs to be applied to crops in the exact amount and on time. In this context, irrigation becomes important in order to reduce risks associated with agriculture. Irrigation is the artificial supply of water to crops for the purpose of agricultural production. There can be various artificial means for supplying water such as canals, wells, tube-wells, tanks etc. which transport water from different sources such as rivers, ponds or underground water.
Need for Irrigation
1. In the next 35 to 45 years, world food production will need to double to meet the demands of increased population.
2. Agriculture requires adequate amount of water throughout the lifecycle of a crop. If the rainfall decreases to less than 30 cm, agriculture becomes impossible without irrigation.
3. India’s rainfall pattern suffers from both – spatial and temporal variations – as well is known for its uncertainty, irregularity, unreliability and erratic nature.
4. India, with her 1.2 billion population, has to have to ensure food security for her citizens through increased agricultural productivity and production and cannot remain dependent on others.
5. Irrigation increases crop yield, protects from famine and also helps in cultivating superior crops with the water supply as per need of the crops.
6. Irrigation maintains moisture in the soil. Moisture is necessary for the germination of seeds.
7. Crops like rice, jute, sugarcane, etc. need more water, which can be fulfilled only through irrigation.
8. New and high-yielding seeds need additional water through irrigation for higher
9. Agricultural activities provide employment to more than 50 % of the total workforce in India so we need to reduce the risk associated with agriculture and increase its productivity to provide better returns to farmers.
Types of Irrigation System
1. In India, the irrigated area consists of about 36 per cent of the net sown area.
2. There are various types of systems of irrigation practices in different parts of India which differ in how the water obtained from the source is distributed within the field.
3. In general, the goal is to supply the entire field uniformly with water, so that each plant has the amount of water it needs, neither too much nor too little.
Irrigation System Based on Source
Depending on the way irrigation water is conveyed to the head or upstream point of a field, irrigation system can be categorized as following:
1. Tank Irrigation
A tank is a water storage system developed by constructing a small bund of earth or stones built across a stream. The water impounded by the bund is used for it. The ratio of tank irrigated land to the total irrigated area of the country has reduced from 14 per cent in the 1960-61 to about 4.6 per cent in 2000-01, primarily due to increase in well and tube well irrigation and partly due to fall in the tank irrigation.
(i) Areas where Tank Irrigation is Prevalent
(a) In peninsular area, tank irrigation is prevalent in Andhra Pradesh, Telangana, Tamil Nadu, Karnataka plateau, eastern Madya Pradesh, eastern Maharashtra, interirio Orissa and Kerala.
(b) Outside the Peninsular plateau, West Bengal, Bihar, Bundelkhand area of Uttar Pradesh, Rajasthan and Gujarat have tank irrigation.
(ii) Merits of Tank Irrigation
(a) Most of the tanks are natural and do not involve heavy cost for their construction.
(b) Tanks are generally constructed on rocky bed and have longer life span.
(c) In many tanks, fishing is also carried on, thus, supplementing both the food resources and income of the farmer.
(iii) Demerits of Tank Irrigation
(a) Many tanks dry up during the dry season and fail to provide it when it is needed the most.
(b) Silting of the tank bed is a serious problem and it requires desilting of the tank at regular intervals.
(c) Much water is evaporated from the large expanse of shallow water and is thus not available for irrigation.
(d) Lifting of water from tanks and carrying it to the fields is a strenuous and costly exercise which discourages the use of tanks as a source of irrigation.
2. Wells and Tube Wells
A well is a hole dug in the ground to obtain the ground water. An ordinary well is about 3-5 metres deep but deeper wells may go up-to 15 metres. This method is being used since time immemorial to lift the ground water for this, drinking, bathing and for other purposes.
(ii) Areas of Well Irrigation
(a) Well it is more popular in those regions where ground water is in plenty and where there are few canals.
(b) These areas include a large part of the Great Northern Plain, the deltaic regions of the Mahanadi, the Godavari, the Krishna and the Cauvery, parts of the Narmada and the Tapi valleys and the weathered layers of the Deccan Trap and crystalline rocks and the sedimentary zones of the Peninsula.
(c) However, the greater part of the Pennisular India is not suitable for well irrigation due to rocky structure, uneven surface and lack of underground water.
(d) Large dry tracts of Rajasthan, the adjoining parts of Punjab, Haryana, and Gujarat and some parts of Uttar Pradesh have brackish ground water which is not fit for irrigation and human consumption and hence unsuitable for well irrigation.
(iii) Tube Wells
A tube well is a deeper well (generally over 15 metres deep) from which water is lifted with the help of a pumping set operated by an electric motor, a diesel engine or solar power. In several areas, the ‘Persian wheel’ earlier used for lifting water has been replaced by tube wells. A tube well cannot be constructed everywhere and requires some geographical conditions favouring its installation, such as:
(a) There should be sufficient quantity of ground water because a tube well can generally irrigate 2 hectares per day against 0.2 hectares per day irrigated by an ordinary well.
(b) The water level should be nearly 15 metres. If the water table is more than 50 metres deep the cost of pumping out water from the tube well becomes uneconomic.
(c) There should be regular supply of cheap electricity or diesel so that water from the tube well can be taken out at the hour of need.
(d) The soil in the immediate neighbourhood of the tube-well should be fertile so that there is demand for irrigation and the cost involved in the construction and operation of the tube well can be recovered by the increased farm production.
(iv) Major Areas under Tube Wells
More than three fourths of India’s tube wells are functioning in Tamil Nadu, Maharashtra, Andhra Pradesh, Telangana, Uttar Pradesh, Madhya Pradesh, Karnataka and Punjab.
3. Canal Irrigation
(i) Canals used to be the most used source of irrigation up-to 1960s, but in the 1970s they wells and tube wells became most used source of irrigation and now, canals constitute the second most important source of irrigation in India.
(ii) Canals are an effective source of irrigation in areas of low level relief, deep fertile soils, perennial source of water and extensive command area.
(iii) Therefore, the main concentration of canal irrigation is in the northern plain of India, especially the areas comprising Uttar Pradesh Haryana and Punjab.
(iv) The digging of canals in rocky and uneven areas is difficult and uneconomic. Thus the canals are practically absent from the Peninsular plateau area.
(v) However, the coastal and the delta regions in South India do have some canals for irrigation.