What is irrigation?
Irrigation is the application of water to the soil for the purpose of supplying moisture essential for plant growth especially during stress periods. It is necessary for the survival and proper devlopment of the crop plants and provide sufficient moisture for the germination of seeds as they do not germinate in dry soils. Similarly, roots of crop plants fail to develop and elongate in dry soil. Also, irrigatton is essental for the absorption or nutrient elements by the crop plants from the soil.
The irrigation requirements of crop plants responseble on the following two factors
(1) irrigation depending on the nature of the crop plants (i.e, crop-based irrigation);
(2) irrigation depending on the nature of soil of the crop fields (i.e., soil-based irrigation)
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, paddy crop (rice crop) is transplanted in standing water (wet-lands) and requires continuous water supply, whereas, other crops such as wheat, gram and cotton require less water.
Soil based irrigation: –
The crops grown in a sandy soil need irrigation nmore frequently, whereas the frequency of irrigation is comparatively less tor crops grown in a clayey soil. This is because sandy soil is highiy porous having high permeability. Water quickly percolates down the soil and the crop plants are not able to absorb adequate amounts of water. In contrast to sandy soil, clayey soil is much less permeable, so it can retain water for a much longer time.
Dought and poor rainfall pose a serious threat to rainfed farming areas. These areas need supply of water from external soùrces. Under such conditions, irrigation system is adopted to supply. water from diffenent water resources Some common irrigation systems are discussed below
1) Wells: –
These are wells are constructed wherever exploitable groundwater is present. there are two types of wells
(A) Dug wells : These are open wells where water gets collected from water bearing strata. They are owned privately by the farmers. They do not have long life and soon become dry whenever water table goes down.
(B) Tube wells: Shallow tube wells meant for irrigation are privately owned and water is lifted by bullock operated devices or by electrically operated or diesel operated pumps. They get water from porous soil strata. Deep bore tube wells take water from the deeper strata and have longer life period of many years.
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. Outflow of water in tanks is regulated so that all areas get adequate water for irrigation.
(3) Canal system:
Canals take water for irrigation from rivers, dams, lakes or reservoirs to agricultural land. Canals form an extensive irrigation system. Main canal divides into distributaries,these distributaries ultimately supply water to the individual field or group of fields.
(4) River lift system:
In areas where canal flow is insufficient or irregular due to inadequate water release, this system is very useful, Water is lifted directly from the rivers for supplementary irrigation in areas close to rivers.
Artificial applications of water to the land are through the following methods:
Sprinkler (or overhead irrigation):-
In this system, water is piped to one or more central location within the field and is distributed by overhead high-pressure sprinklers or overhead pipes,
Drip irrigation (or trickle irrigation) :-
In this type of irrigation method, water is delivered at on near the root zone of plants, drop by drop. This is most water efficient method as evaporation and run off are minimised
Historically, this has been the most common method of irrigating agriculture land. Water moves over and across the land by simple gravity flow in order to wet it and to infiltrate the soil.