Definition of Irrigation
The process of artificial application of water to the soil for the growth of agricultural crops is termed as irrigation. It is practically a science of planning and designing a water supply system for the agricultural land to protect the crops from the bad effect of drought or low rainfall. It includes the construction of weirs, dams, barrages and canal systems for the regular supply of water to the culturable (i.e. cultivable) lands.
Necessity of Irrigation
Throughout the crop period, adequate quantities of water are required near the root zone of the plants for their growth. At times during the crop period, the rainfall may not be adequate to fulfil the water requirement. The intensity of rainfall is practically uncertain and beyond the control of human power and it may not be well distributed throughout the crop season or the culturable area. So, irrigation becomes absolutely necessary to fulfil the water requirement of crops. The following are the factors which govern the necessity of irrigation.
When the seasonal rainfall is less than the minimum requirement for the satisfactory growth of crops, the irrigation system is essential.
(b) Uneven distribution of rainfall
When the rainfall is not evenly distributed during the crop period or throughout the culturable area, the irrigation is extremely necessary.
(c) Improvement of perennial crops
Some perennial crops like sugarcane, cotton, etc. require water throughout the major part of the year. But the rainfall may fulfil the water requirement in rainy season only. So, for the remaining part of the year, irrigation becomes necessary.
(d) Development of agriculture in a desert area
In a desert area where the rainfall is very scanty, irrigation is required for the development of agriculture.
Benefits of irrigation
The following are the important benefits of irrigation:
(a) Yield of crops
In the period of low rainfall or drought, the yield of a crop may be increased by the irrigation system.
(b) Protection from famine
The food production of a country can be improved by ensuring the growth of crops by availing the irrigation facilities. This helps a country to prevent famine situation.
(c) Improvement of cash crops
Irrigation helps to improve the cultivation of cash crops like vegetables, fruits, tobacco, etc.
(d) Prosperity of farmers
When the supply of irrigation water is assured, the farmers can grow two or more crops in a year on the same land. Thus the farmers may earn more money and improve their living standard.
(e) Source of revenue
When irrigation water is supplied to the cultivators in lieu of some taxes, it helps to earn revenue which may be spent on other development schemes.
The irrigation canals may be utilised for inland navigation which is further useful for communication and transportation of agricultural goods.
(g) Hydroelectric power generation
In some river valley projects, multipurpose reservoirs are formed by constructing high dams where hydroelectric power may be generated along with the irrigation system.
(h) Water supply
The irrigation canals may be the source of the water supply for domestic and industrial purposes.
(i) General communication
The inspection road along the canal banks may serve as a communication link with the otherwise remote villages.
(k) Development of fishery
The reservoir and the canals can be utilised for the development of fisher projects.
ILL-effects of irrigation
The following are the ill-effects of irrigation:
(a) Rising of the water tables
Due to the excessive seepage of water through the bed and banks of canals, the water table in the surrounding area may be raised which may constantly saturate the root zone of the crops and the soil may develop alkaline property which is harmful to the crops.
(b) Formation of marshy land
Excessive seepage and leakage of water from the irrigation canals may lead to the formation of marshy lands along the course of the canals. These marshy lands form the colonies of mosquitos which may be responsible for diseases.
(c) Dampness in weather
The temperature of the commanded area of an irrigation project may be lowered considerably and the area may become damp. Due to dampness, the people residing around the area may suffer from cold, cough and other such diseases originating from dampness.
(d) Loss of valuable lands
Valuable land may get submerged when storage reservoirs are formed by constructing barrages or dams and, it also may be lost while constructing irrigation canals.
Book – Irrigation Engineering, Writer – N N Basak