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What is Irrigation System?
Crop plants get water from the soil. Soil obtains water from rain. However, sufficient rain is not always available. Therefore, the soil is not able to supply sufficient water to crops. The extra water required by crops is met through irrigation. The process of supplying water to crop plants by means of canals, wells, reservoirs, tube wells, etc. is known as irrigation.
In our country, there are 12 major river basins and 8 composite river basins. Groundwater also contributes significantly to our total water resources. This is replenished by rainfall. However, only 55% of our cropped area is either partly irrigated (about 25%) or under assured irrigation (about 30%). The remaining about 45% of cropped area is unirrigated and is dependent on rain for the cultivation of crops. It is called rainfed agriculture.
The success of rainfed agriculture depends upon timely and sufficient rain during most of the growing season. Scarcity and irregular distribution of rain can cause drought (sookha). Drought-prone areas generally have light soil (sand-rich soil) which is unable to retain water for long. They are, therefore, more affected by drought. Poor monsoons or rains tend to result in crop failure. However, agriculture scientists have developed some crop varieties which can grow in rain-fed areas and survive drought conditions. Water management is arranging and supplying required water to crops without harming soil aeration, changing the water table, or causing water-logging and soil salinity.
Importance of Irrigation in Agriculture
In agriculture irrigation fulfil the following goals:
- Crop plants are irrigated with freshwater to supply two essential elements to them, hydrogen and oxygen. Both of these elements are present in water molecules and are necessary for the growth and development of crop plants.
- Irrigation of crop fields is necessary to provide sufficient moisture for the germination of seeds, as seeds do not germinate in dry soils.
- Irrigation of crop plants is essential for the growth and elongation of the roots of the crop plants. This is because the roots of crop plants fail to develop and elongate in dry soil.
- Irrigation is necessary to increase the number of aerial branches (called tillers) in crop plants so as to get a good crop yield.
- Irrigation is essential for the absorption of nutrient elements by crop plants from the soil.
- The irrigation water tends to dissolve the nutrients present in the soil of a crop field to form a solution.
- This solution of nutrients is then absorbed by the roots of crops for the development of the plants.
Advantages of Irrigation
Irrigation has many other advantages compared to natural rainwater supplies.
- The supply of water by irrigation is regular and reliable, whereas rainfall is often seasonal or unpredictable.
- Irrigation water supplied by rivers in flood often carries silt which adds to the soil of the fields, enhancing fertility and crop yield.
- With irrigation, cultivation can be done around the year and not during the rainy season only.
- In desert areas, the constant flow of irrigation water through the soil helps to reduce the salinity of the soil.
- However, if the water is allowed to evaporate in the fields, the salt content of the soil will increase.
- Modern multipurpose dams not only provide water for irrigation but also help to control floods, generate hydroelectric power, and improve the navigability of the rivers.
Factors Controlling Irrigation
The irrigation or water requirements of crop plants depend on the following two factors:
- Irrigation is dependent on the nature of the crop plants (i.e., crop-based irrigation).
- Irrigation is dependent on the nature of the soil of the crop fields (i.e., soil-based irrigation).
1. Crop-based irrigation:
Water requirements of different crops are different during the various stages of their growth and maturation (ripening). Some crop plants require more water, while others need less water. For example, the paddy crop (rice crop) is transplanted in standing water (wetlands) and requires a continuous water supply, whereas, other crops such as wheat, gram, and cotton require less water. For cereals such as wheat, irrigation is required before ploughing the field (i.e., before tilling), at the time of flowering, and at the time of development of the grain.
2. Soil-based irrigation:
Irrigation also depends on the nature of the soil in which the crop is grown. The crops grown in sandy soil need irrigation more frequently, whereas the frequency of irrigation is comparatively less for crops grown in clayey soil. Let us find out why this occurs Sandy soil is highly porous and has high permeability.
When the crop plants standing in sandy soil are irrigated, water quickly percolates down the soil and the crop plants are not able to absorb adequate amounts of water. So, due to the poor water retaining capacity of the sandy soil, the crops cultivated in sandy soil need more frequent irrigation. In contrast to sandy soil, clayey soil is much less permeable, so it can retain water for a much longer time.
So, when the crops grown in clayey soil are irrigated, the water persists in the soil for a longer time and as a consequence plants grown in clayey soil can absorb this water in adequate amounts. Thus, due to the good water-retaining capacity of the clayey soil, the crops cultivated in clayey soil need irrigation less frequently.
Different Types and Methods of Irrigation Systems
Our country is blessed with large water and land resources with varied climatic conditions. Under such circumstances, various types of irrigation systems have been adopted to supply water to agricultural lands. Some most commonly used irrigation systems are the following:
1. Canal System:
In a canal system, the human-made canals receive water from one or two reservoirs or from rivers. This is usually an elaborate and extensive irrigation system. Thus, the main canal is distributed into branch canals and branch canals further have distributaries or field channels. These unlined field channels may serve individual fields or a group of fields. Under the canal irrigated areas, the rotation system is followed. Rotation system is known as water bandhi or intermittent water delivery method. This provides adequate irrigation to all the fields when the water supply is short. Each field or group of fields is given water by rotation.
Tanks are small storage reservoirs, which catch and store the runoff of smaller catchment areas. Small dams are built below the higher elevations of the catchment areas. In the tanks, outflows are controlled according to the availability of water. Otherwise, it causes an uneven distribution of water. The main drawback of uneven distribution of irrigation water is that it causes a shortage of water at the tail end and excessive use at the top.
Wells are constructed wherever exploitable groundwater is present. Wells are of two types:
- Dug wells: In the dug wells, the water is collected from water-bearing strata. These dug wells have
their base below the groundwater table. The water from the shallow strata slowly accumulates in the pit. From these wells, water is lifted by mechanical means, e.g., bullock-operated devices.
- Tube wells: A tube well can tap water from the deeper strata. From these wells, water is lifted by diesel or electricity-run pumps. A deep bore tube well can supply water continuously for many years.
- Wells and tube wells are successful in those areas where underground water is not saline, in areas where underground water is saline, canal water is used for irrigation.
- Excessive irrigation causes water logging and increases surface salinity. In water-logged soil plants, roots do not get proper aeration.
4. River Lift System:
A river lift system is more useful in those areas where canal flow is insufficient or irregular due to inadequate water release. In this system, water is directly drawn from the rivers for supplement irrigation.
5. River Valley System:
Certain parts of the country such as Karnataka and Kerala which lie along the Western Ghats, use water that is discharged into the steep and narrow riverine valleys, during the rainy season. In these parts of India, the rainfall is heavy but concentrated in four or five months period of the year. This is followed by drying up during the rabi season. On the slopes of these valleys and in the valleys perennial plants (= crops) such as coconuts, areca nuts (supari), coffee, rubber, and tapioca are cultivated. The bottom flat lands of the valleys are used for growing a single rice crop.
The sprinkler irrigation system is being introduced in canal-irrigated areas of Haryana, Rajasthan, and Madhya Pradesh.
The drip irrigation system is being encouraged in Maharashtra, Karnataka, Andhra Pradesh, Orissa, and Tamil Nadu for fruit crops. Fertigation is an innovation of applying fertilizer through drip irrigation to maximize farm productivity with available water.
6. Drip and Sprinkler System:
Overhead pipes for spraying water and sprinkler systems save a lot of water and are more natural. They, however, require a pumping system. These methods are very common in the U.S.A., Britain, Europe, and parts of India.
Water availability for irrigation can be assured by augmenting groundwater. It is carried out by following two methods.
- Rainwater harvesting: Rainwater is not allowed to go to waste. It is collected and used for recharging groundwater by sinking deep drain pipes. It can also be poured into wells or used to recharge ground water by digging up wells.
- Watershed management: Small check dams are built up in watershed areas to increase the percolation of water into the ground, reduce the flow of rainwater and prevent soil erosion.