Dr. Anuradha Saha and
Dr. Vijay Bharti
Water is called elixir of life and is available in plenty on earth. According to the UN estimation, the total amount of water on earth is estimated at 1400 M km3. Out of total water resources of earth, only 2.7% are fresh water of which 75.2% lies frozen in Polar Regions, 22.6% as ground water and the rest in lakes, rivers, atmosphere, soil and vegetation. Consumption of water is the small fraction of water available in rivers, lakes and ground water.
In many parts of tropical Asia, rice plants suffer from either too much or too little water because of irregular rainfall and landscape patterns. In India, rice is grown under diverse agro ecological conditions and is largely dependent on monsoonal rains and its distribution which also influences the production potential of the system. Depending on the topography, the crop is exposed to extreme hydrological conditions of near dry soil moisture in uplands and shallow low lands (drought) to water stagnation up to 5 m level (flooding and submergence) besides several soil and management stresses of excess salts (salinity, alkalinity), acidity and nutrient deficiency and toxicity.
Rice is known as an inefficient water user crop, as it consumes about 4000-5000 litres of water to produce a kg of grain. Rice is most sensitive to moisture stress from 20 days before heading to 10 days after heading. The water requirement of rice is low at the seeding stage. Immediately after transplanting, sufficient water should be provided to facilitate early rooting. Following the early rooting stage, a shallow water depth facilitates tiller production and promotes firm root anchorage in the soil. The last phase of the growing period includes the milk, dough, yellowish and full grain ripening stages, very little water is needed at this period and after the yellowish ripening stage no standing water is required.
In India, about 52% of total rice area is irrigated (24 m ha) which contributes more than 75 % to the total rice production in the country. Large investments have been made since independence to develop irrigation facilities. But the existing irrigated rice cultivation practices are water intensive. Moreover, a large amount of non-productive water is lost from rice field through seepage, percolation and evaporation which decrease the water use efficiency.
On the other hand, the ever increasing cross sectoral demands (industrial, urbanization) for water and land is gradually reducing the share of water for agricultural use in general and for rice cultivation in particular, which is projected to decrease the per capita water availability from 2500 m3 / year in 1990 to 1500 m3 / year in by 2050. Further, the availability of water for agriculture may drastically go down thus putting enormous pressure on rice cultivation. Therefore, there is need to improve its water use efficiency with the objective of more rice crop from every drop of water.
For a farmer, “water saving” is likely to mean using less irrigation water to grow a crop-ideally with the same or higher yield (or ultimately profit), thus increasing irrigation water productivity. However, irrigation water saving does not necessarily mean that total water use (from rain and soil water as well as irrigation) is reduced at field scale.
Water saving in agriculture is ultimately about reducing non-beneficial losses-losses that can’t be economically recaptured elsewhere in agriculture. These non-beneficial losses are evaporation from the soil and surface and deep drainage into water to contaminated for reuse (e.g. saline ground water, the sea) or into locations from which it is too difficult to recapture (e.g. aquifers with low transmissivity).
New water cannot be created; thus we have to conserve and make judicious use of every drop. Two possible options are to minimize water losses through better management thus ensuring more water for crop production, and improve water use efficiency i.e. increase in production per unit of water. Other option is choice of crops according the soil. Because, soil type influences the need for irrigation water e.g. coarse-textured soils have higher percolation losses. Land leveling also facilitates uniform water application in less time and helps in weed control.
Although water is a nature’s gift, it has become priceless due to its decreasing availability. Like all other agricultural inputs it is also pertinent to assess the efficiency of applied water and its range under different management practices. Current scenario of water resources indicate that it is not possible to continue the way water is used for rice cultivation, since the expected 10% cut in irrigation water supplies to agriculture in the next decade, due to cross sectoral demands viz., domestic, industrial and other sectors. Further the predicted climate changes are likely to accentuate the impending water crisis. There is need to economise water use for rice production based on the objective assessment of the crop need. There is need of a paradigm shift towards maximizing output per unit of water instead of per unit of land. There is an urgent need for development and the adoption of water management technologies for rice that follows three important principles: rice ecology; integrated water resource management; and sustainability. Adoption of improved soil and water management practices by farmers to avoid unproductive water losses via percolation, seepage, run-off, evaporation and improve crop productivity through synchronization of irrigation at critical stages of plant growth. Such methods help produce more rice per given unit of water. Producing more food with less water may be the only viable option to ensure food security and sustain natural resources system in the long run provided it is implemented on a large scale with the involvement of all end users. For farmers with limited supply of water, improving water productivity is a boon to expand area under irrigation and thus improve income livelihoods. In rice, production has to come from lesser and lesser resources (land, water, labour etc.) with due consideration given to keep the environment safe and continuously enhance profitability in rice cultivation. Most importantly, there is an urgent need to change the mindset of farmers that successful rice crop can be grown without the standing water in the field. Concerted efforts in reviving the water saving technologies, demonstrating them in farmer’s field and extensive campaigns to save water in rice cultivation would go a long way to sustain rice production even under the threat of severe water crisis.
(The authors are Agronomist, SKUAST-Jammu, Chatha.)
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