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

More documents

Recommendations

Info

Distribution (%)100908070605040302010Through-flowManila01968 1973 1978 1983 1988 1993 1998YearAWater allocation (10 6 m 3 )800700B600500400300IrrigationOther uses20010001965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998Fig. 1.6. (A) “Imposed water scarcity”: change in percentage water allocation from Angat reservoir, Philippines, to throughflowin the river for potential agricultural use downstream and to the city of Manila. Data from Pingali et al (1997) andunpublished data from the National Irrigation Administration, Philippines. (B) “Imposed water scarcity”: change in waterallocation to agricultural and nonagricultural use in Zanghe Irrigation System, Hubei, China, between 1965 and 2002. Datapoints are 5-year moving averages. Data from Hong et al (2001) and unpublished data.Yearto cut down on costs if irrigation water is expensive.However, for most rice farmers, there is no deliberatechoice to save water as they are just confrontedby a lack of water. Under such conditions, savingwater simply means coping with scarcity. Thus,the objectives of saving water depend on the natureof the water scarcity and the control farmers haveover the water. Drawing parallels with generaldefinitions of “savings,” we discuss three reasonsfor saving water:Definition 1: to reduce current expenditures onone commodity to allow for redirected expenditureson other commodities. In water terms, this translatesinto “reducing water used for irrigation so that itcan be used for another purpose.” In agriculture, themotivation for this type of water savings is usuallynot an absolute shortage of water but a desire to usethe available water not for irrigation but for otherpurposes such as domestic or industrial. Increasingcompetition for water between sectors of society isthe driving force behind such savings in agriculturalwater use. The examples of what is happening inthe Zanghe Irrigation System in China and at theAngat reservoir in the Philippines are a case inpoint: the managers of these reservoirs are reducingthe amount of water released for agricultureand redirecting this water to cities (Manila, in thecase of Angat) and to industry and hydropower (inthe case of Zanghe) (Loeve et al 2004a,b; Fig. 1.6).These water savings in agriculture are not an activeand deliberate choice by farmers. The choice towithdraw water from agriculture is made at a higher
level: the irrigation system, provincial, or nationallevel. Farmers must face the consequences of thesedecisions: they receive less water and have to copewith “imposed water scarcity.” The notion that weshould ask farmers to actively save water so it canbe used elsewhere, such as by industry and cities,is a fallacy. Farmers can be encouraged to voluntarilyreduce water use, for example, by introducingvolumetric water pricing, but this is the exceptionrather than the rule and “enforced water scarcity” isprevalent. Voluntary water savings by farmers forredirected use work well only with properly functioningwater markets. For example, in Australia,rice farmers in irrigation schemes in the Murraybasin can sell their water rights in a water market toother users, such as other farmers who grow highvaluecrops such as fruits (Thompson 2002).Definition 2: to reduce expenditures becauseof reduced income. In water terms, this translatesinto “reducing the use of irrigation water becausethere is less of it.” This type of water savings inagriculture is induced by actual and physical waterscarcity. An example of this situation for farmersis the “enforced water shortage” discussed above.However, an absolute water shortage can also beinduced by natural causes. For example, when seasonalrains have failed to fill up reservoirs or ponds,the amount of water may not be sufficient to keepall rice fields flooded throughout the year. Whenthe reservoir forms part of a large-scale irrigationsystem, reservoir managers usually respond byreducing the “program area” for irrigation: fewerfarmers will receive irrigation water. However, withsmaller reservoirs such as individual ponds, farmersthemselves can decide how to cope with the waterscarcity. They may decide to reduce their land underirrigation or they could decide to “reduce currentexpenditures to allow for future expenditures”: todeliberately save water early in the season to have itavailable later in the season. Farmers can save waterby reducing the amount of irrigation applied to theirfields early in the season. The best way to do this isby reducing the nonproductive outflows seepage,percolation, and evaporation (Chapter 3).Definition 3: to reduce costs to increase profit.In water terms, this translates into “reducing theuse of irrigation water to lower the costs.” Thisscenario is applicable when farmers pay a high costfor water and have the means to reduce their wateruse to increase their profits. There may be plentyof water, but it is relatively expensive (“economicwater scarcity”). In most surface irrigation systemsin Asia, farmers either pay no cost for their water orpay a flat rate (a fixed sum per unit land area), andwater costs cannot be reduced by reducing wateruse. When farmers pump their own water, eitherindividually or collectively, they pay a relativelyhigh price for their water when pumping is fromdeep aquifers and/or when the price for electricityor fuel is high. In this case, water savings byfarmers are a voluntary and deliberate choice oftheir own. The means to save water are the sameas in the scenario above: to reduce irrigation waterto their fields.These examples illustrate that water scarcity isusually imposed upon farmers (either by nature orby decision makers at higher levels) and that savingwater is hardly a voluntary choice (except in definition3). Farmers just have to cope with physicalwater scarcity, and the term “water-scarcity copingtechnology” may be more appropriate than the term“water-saving technology.”10
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 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 46 and 47: the main system is supply-driven, f
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

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?