Water management in irrigated rice - Rice Knowledge Bank ...

the main system is supply-driven, farmers havecontrol over the timing and amount of water at thefarm gate because water is stored in small farmponds, which can also provide water for other uses(Mushtaq et al 2006).5.2 Field versus irrigation system levelThe relationships between water use at the fieldand at the irrigation system level are complex andinvolve hydrological, infrastructural, and economicaspects. At the field level, farmers can reduce waterlosses by adopting water-saving technologies(Chapter 3). If they pay for the cost of the waterthey use, they can thereby increase the profitabilityof rice farming. At the irrigation system level, theadoption of field-level water-saving technologieswill reduce the total amount of water lost as evaporation,but by relatively small amounts only. Mostof the water saved at the field level is by reducedseepage, percolation, and drainage flows. On theone hand, this results in more water retained at thesurface (in the irrigation canals), which is availablefor downstream farmers. On the other hand,it reduces the amount of water re-entering the hydrologicalcycle and thus reduces the options forinformal reuse downstream. Reducing percolationfrom rice fields can lower groundwater tables. Thiscan adversely affect yields since rice plants may beless able to extract water directly from the groundwater(Chapter 1.4; Belder et al 2004). Deepergroundwater tables will also increase the cost ofpumping for reuse downstream. Any adoption ofwater-saving technologies requires considerablewater control by the farmers. This is not much ofa problem for farmers using their own pump, butit is so for farmers in large-scale surface irrigationsystems that lack flexibility in, and reliability of,water delivery. It is also a problem for farmers usingelectricity to pump groundwater where supplies areunreliable, as in northwest India. To allow farmersto profit from water-saving technologies, suchirrigation systems need to be modernized, whichcomes at an economic cost.The “beneficiaries” of water savings at thefield and irrigation system level are different in mostcases. At the irrigation system level, the irrigationsystem management can save water in agricultureand use this water for other purposes such as hydropowergeneration or industry. Farmers will beinterested in saving water only if they can derivebenefits such as reduced irrigation costs. A detaileddiscussion of motives to save water is presented inChapter 1.7.5.3 Integrated approachesApproaches that integrate agronomic measures,improved policies, institutional reforms, and infrastructuralupgradings may have the best chance ofsuccessfully responding to water scarcity. A recentsuccess story is the Zanghe Irrigation System (ZIS)in the middle reaches of the Yangtze Basin in China(Loeve et al 2004a,b). ZIS has a command area ofabout 160,000 ha and services mainly rice in thesummer season. Since the early 1970s, the amountof water released to agriculture has been steadilyreduced in favor of increased releases to cities,industry, and hydropower (Fig. 5.4). Since the mid-1990s, the amount of water received by agriculturehas been less than 30% of the amount received inthe early 1970s. In the same period, however, totalrice production has increased, with a productionpeak of around 650,000 tons in the late eighties thatwas nearly twice the amount produced in the latesixties. Although rice production has leveled off toa stable 500,000 tons in the last decade, more ricehas been produced with less water over the past 30years. This feat has been accomplished by a varietyof integrated measures (Dong et al 2004, Hong etal 2001, Loeve et al 2001, 2004a,b, Mushtaq et al2006, Moya et al 2004): Double rice cropping has been replaced bymore water-efficient single rice cropping.This was possible because of the availabilityof modern short-duration high-yielding varieties. The alternate wetting-drying water-savingtechnology has been promoted and widelyadopted. Policies, such as volumetric water pricing,and institutional reforms, such as water-userassociations, have been introduced that driveand promote efficient use of water by farmers. The irrigation system has been upgraded (e.g.,canal lining). Secondary storage has been developedthrough the creation of thousands of small- tolarge-size ponds and reservoirs.The ZIS case study suggests that win-winsituations can exist where rice production can be41