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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
Water for irrigation (10 6 m 3 )1,4001,200Rice production (000 t)8007001,000Water600800600400200019651969 1973 1977 1981 1985 1989 1993 1997 2001YearRice5004003002001000Fig. 5.4. Total rice production and irrigation water supply in Zanghe Irrigation System, Hubei, China, between 1965 and2002. Data points are 5-year moving averages. See also Fig. 1.6B from Hong et al (2001).maintained, or even increased, while freeing upwater for other purposes.5.4 Irrigation system managementWhen water is scarcer than land, it may be beneficialto maximize water productivity rather than landproductivity (which is yield; kg ha −1 ) in irrigationsystem management. Take, for example, a typicalrice-based irrigation system that faces water shortagein the main reservoir. A usual response optionof the irrigation system manager is to programless area for irrigation than the designed commandarea. In practice, this means that upstream farmerswould get sufficient water for flooded rice production,and downstream farmers would not get anywater at all and their land would be left fallow.However, to maximize total production from theirrigation system, and to improve equity amongfarmers, it would be more beneficial to spread outthe available amount of water over the completecommand area and “impose” some water scarcity onall farmers. Instead of upstream farmers practicingcontinuously flooded irrigation, and downstreamfarmers having no water at all, there could be amix of farmers growing flooded rice and adoptinga water-saving technology such as AWD. Table 5.1quantifies the water use and total rice production ofa hypothetical irrigation system in two contrastingscenarios of water distribution. The productivityand water-use parameters of flooded rice and AWDrice used in our example are taken from Table 3.2(Guimba, 1989 data), and are repeated in Table 5.2.To simplify the calculations, we assume there is norainfall and that all water is supplied by irrigation.The system is 10,000 ha, with a storage capacity ofthe reservoir of 168 10 6 m 3 . With a full reservoir,this amount of water is sufficient to have 10,000 haof flooded rice, producing a total of 58 10 3 tons ofrice. Suppose there is a water scarcity and that thereservoir is filled only to 80%, storing 134 10 6 m 3of water. In scenario I, only 80% of the commandarea receives water, allowing these farmers to growflooded rice, whereas the remaining 20% is leftfallow. In scenario II, 65% of the command areareceives the “full” amount of water, allowing thesefarmers to grow flooded rice, and the remaining35% receives a reduced amount that is sufficientto grow rice under AWD. In scenario I, the totalrice production in the irrigation system is 46 10 3tons, and, in scenario II, it is 53 10 3 tons. Moreover,there is more equity among the farmers in scenarioII than in scenario I.The above example is quite simple (and ignoresthe complexities of diversified cropping and of systemsoperation to allow farmers to practice AWD)42
Page 2: Water Management in Irrigated Rice:
Page 5 and 6: PrefaceWorldwide, about 79 million
Page 8 and 9: Fig. 1.2. Water balance of a lowlan
Page 10 and 11: given in Table 1.1. Water losses by
Page 14 and 15: Distribution (%)1009080706050403020
Page 16 and 17: The plant-soil-water system22.1 Wat
Page 18 and 19: Ψ Air-100 MPaDemandLeafXylemStemRo
Page 20: tive to water deficit than cell enl
Page 23 and 24: Water input (mm)4003503002502001501
Page 25 and 26: Table 3.1b. Yield, water input, and
Page 27: Grain yield (t ha -1 )98A2002 20037
Page 30 and 31: Table 3.5. Water input (I = irrigat
Page 32 and 33: Practical implementationTemperate e
Page 34 and 35: Practical implementationSpecific in
Page 36 and 37: Table 3.8. Comparison of water use
Page 38: Flooded yield (t ha -1 )87A65432102
Page 41 and 42: consumption (Hamilton 2003). Many t
Page 44 and 45: Irrigation systems55.1 Water flows
Page 48 and 49: Table 5.1. Area, water use, and tot
Page 50 and 51: Appendix: InstrumentationDetailed d
Page 52: 0.5 cm in diameter and spaced 2 cm
Page 55 and 56: Bronson KF, Singh U, Neue HU, Abao
Page 57 and 58: Lampayan RM, Bouman BAM, De Dios JL
Page 59: Uphoff N. 2007. Agroecological alte

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