Water for irrigation

Dr Ramesh Kumar Thusoo
One of the basic needs of human life is the water which is becoming increasingly scarce worldwide due to various reasons. This fact has compelled various organizations to think about its conservation and most efficient use for the survival of the humanity and its eco system. Most of the countries located in arid and semi-arid regions, the problems of water scarcity is expected to be aggravated further .Macro-level estimate carried out by the
International Water Management Institute (IWMI), Colombo, indicates that one-third of  the world population would face absolute water scarcity by the year 2025. As per this estimate, the worst affected areas would be the semi-arid regions of Asia, the Middle-East and Sub-Saharan Africa, all of which are already having heavy concentration of population living below poverty line. Studies carried out across different countries including India have confirmed that irrigation plays a vital role in increasing the use of yield increasing inputs and  enhancing cropping intensity as well as productivity of crops. The well developed irrigation system plays a lot in terms of increasing returns   and employment of the agricultural community and also of land less laborers, which are essential to reduce the poverty among the general mass.
In spite of having the largest irrigated area in the world, India too has started facing  Sever water scarcity in different regions. Owing to various reasons the demand for water  for different purposes has been continuously increasing in India, but the potential water  available for future use has been declining at a faster rate. Though India has the largest irrigated area in the world, the coverage of irrigation is only about 40  percent of the gross cropped area as of today. One of the main reasons for the low coverage of irrigation is the predominant use of flood (conventional) method of irrigation, where water use efficiency is very low due to various reasons. Available estimates indicate that water use efficiency under flood method of irrigation is only about 35 to 40 percent because of huge conveyance and distribution losses. While the various strategies introduced to improve the water use efficiency have been continuing, the net impact of these strategies in increasing the water use efficiency is not very impressive as of today. One of the demand management strategies introduced relatively recently to control water consumption in Indian agriculture is micro irrigation which includes mainly drip and sprinkler irrigation method.
Under micro-irrigation, unlike flood method of irrigation, water is supplied at a   required interval and quantity using pipe network, emitters and nozzles. Therefore, the conveyance and distribution losses are reduced completely which result in higher water  use efficiency under micro irrigation. Though both drip and sprinkler irrigation method of irrigation is treated as MI, there are distinct characteristics differences between the two in terms of flow rate, pressure requirement, wetted area and mobility. While drip method supplies water directly to the root zone of the crop through a network of pipes with the help of emitters, where as  in  sprinkler irrigation method water is supplied similar to rainfall into the air through nozzles which subsequently break into small water drops and fall on the field surface. The on-farm irrigation efficiency of properly designed and managed drip irrigation system is estimated to be about 90 percent, while the same is only about 35 to 40 percent  for surface method of irrigation. In sprinkler irrigation method, water  saving is relatively low (up to 70 percent) as compared to drip irrigation .
Micro-irrigation is introduced primarily to save water and increase the water use  efficiency in agriculture. While increasing the productivity of crops significantly, it also reduces weed problems, soil erosion and cost of cultivation substantially, especially in labour-intensive operations. The reduction in water consumption in micro-irrigation also reduces the energy use (electricity) that is required to lift water from irrigation wells.
Closely grown crops such as millets, pulses, wheat, sugarcane, groundnut, cotton,  Vegetables, fruits, flowers, spices and condiments have been found to be suitable to  cultivate under sprinkler irrigation. Given the population growth and increasing requirement of agricultural commodities, there is a need to increase the area under cultivation. Micro-irrigation can be one of the viable options for expanding area under cultivation.  Though remarkable growth has been achieved over the last 15 years  in adopting micro-irrigation, its share to the gross irrigated area of the country is only  negligible percent as of today. Among the various reasons for the slow progress of  adoption of this new technology, seems to be  capital intensive nature which may be one of the  main deterrent factors. Micro-irrigation technology requires fixed investment that varies from  Rs. 20,000 to Rs. 55,000 per hectare depending upon the nature of crops (wide or narrow  spaced) and the material to be used for the system. Since the Indian farmers have been   getting water for low cost from the public irrigation system and also from well irrigation (because of free and flat-rate electricity tariff), there is less incentive to them to adopt this capital-intensive technology unless it is necessary .Considering the limited potential of water resources as well as growing demand for  water from different purposes, it has become essential to adopt Water Saving Technologies  so as to avoid the water stress in the future. It has been proved by studies that drip and sprinkler method of irrigation helps to save water and improves water  use efficiency.
While reducing water consumption, it also reduces substantial amount of electricity required for irrigation purpose, by reducing working hours of irrigation pump sets. There are various other reasons for enormous water savings under drip method of irrigation. As water is supplied through a network of pipes, the evaporation and distribution losses of water are very minimum or completely absent under drip irrigation method , water is supplied under drip irrigation method at a required time and required level and thus, over-irrigation is totally avoided. Lastly under the conventional method of irrigation, water is supplied for the whole cropland, whereas drip irrigation irrigates only the plants. Our planners and development agencies need to enforce such system as will give more profitability in less cost and even un irrigated areas can also be taken care off in the near future. In states like Karnataka . Maharashtra Andhra Pradesh, the micro irrigation system is developing at a faster rate and employment in floriculture, olericulture and horticulture is increasing at a faster rate  and benefiting the farming community .

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