Definition, objective and importance of irrigation
Irrigation generally is defined as the application of water to the soil for the purpose of supplying moisture essential for plant growth.
Irrigation is essential for crop production. Following are the objectives of irrigation-
1. To supply water for the nutrition and growth of plant.
2. To leach or wash out injurious salt from the soil.
3. To remove the stress (moisture deficit) condition of plants.
4. To release nutrients in soil solution for absorption by plants.
5. To keep the activity of soil microbes at the optimum level and to hasten the decomposition organic matter in the soil.
6. To maintain the temperature and humidity of the soil.
7. To control harmful soil insects.
8. To create water stagnation for controlling dry land weeds.
9. To create condition suitable for puddling.
10. Irrigation is necessary to reclaim fallow land and sometimes, to bring desirable condition for tillage.
Plants must be supplied with water as required them for successful crop production. Irrigation is necessary for crop production due to following reasons:
1. Uncertainty of monsoon rainfall: Monsoon wind cause 80 per cent rainfall in Bangladesh. But the monsoon rain is very uncertain. There is no liked schedule that exactly when the rain start and what will be the duration of the, season. In fact these are variable for every year. So irrigation is very important to supply water to plants as and when needed i.e. at the right time and in correct amount.
2. Uneven distribution of rainfall: Rainfall is uneven in all the places of Bangladesh. Irrigation is essential for crop production in an area having low and uncertain rainfall.
3. Winter rainfall:Rainfall is rare in winter season in our country. Rabi crops need much water for their growth and development. Therefore, irrigation is very important for the cultivation of Rabi crops. The cultivation of boro rice is impossible without irrigation.
4. Cultivation of high yielding crops: The high yielding crops are being cultivated in our country which require sufficient water for their growth and development. Irrigation has the key role to play for the successful cultivation of high yielding crops.
5. Difference in water-holding capacity of soil: There are different types of soil in our country having difference in water holding capacity. In such cases, irrigation must be provided depending on the soil texture.
Rainfall is the primary source of water for irrigation. But it is not available throughout the year in all arable areas and in appropriate quantities required by each crop variety at the different stages of its growth. Rainfall reserved in other water bodies is used as resources of irrigation water for an indefinite time. Following are the sources of irrigation water:
Surface water: Surface water is provided by flowing water of river of from still waters of tanks, ponds, lakes pools or artificial reservoirs such as dams, barrages and diversionary bunds with different storage capacity. Water from these sources is carried to the field by lifting them with the help of water lifting devices used for irrigation.
Ground water: Water is reserved underground enriched by percolation of the surface water through the porous state of earth crust land this type of water is known as ground water. The subterranean water tapped by digging or drilling wells. Wells may be shallow (9- 11 m) or deep (25-30 m or more) the water front wells is lifted to be used for irrigation.