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Ecosystem services andthe environment44.1 Ecosystem servicesAlthough the main function of rice fields is toproduce rice, they also provide a range of other“ecosystem services” (also referred to as “multifunctionality”)(Bouman et al 2006a). Ecosystemservices can be grouped into the following categories(Millennium Ecosystem Assessment 2005): Provisioning (e.g., fresh water and commoditiessuch as food, wood, timber, and fuel) Regulating (e.g., water purification, and climateand flood regulating) Supporting (e.g., nutrient cycling, soil formation,primary production) Cultural (e.g., aesthetic, spiritual, educational,recreational)The most important provisioning function ofrice environments is, of course, the production ofrice. Examples of other provisioning services arethe raising of fish and ducks in rice fields, ponds, orcanals. Frogs and snails are collected for consumptionin some countries.As part of regulating services, bunded ricefields may increase the water storage capacity ofcatchments and river basins, lower the peak flowof rivers, and increase groundwater flow. For example,in 1999 and 2000, 20% of the floodwaterin the lower Mekong River Basin was estimated tobe temporarily stored in upstream rice fields (Masumoto2004). Other possible regulatory services ofbunded rice fields and terraces include the preventionor mitigation of land subsidence, soil erosion,and landslides (PAWEES 2005). Percolating waterfrom rice fields, canals, and storage reservoirsrecharges groundwater systems (Mitsuno 1982).The moderation of air temperature by rice fieldshas been recognized as an important function inperi-urban areas where rice fields and urban land areintermingled (Oue 1994). This function is attributedto relatively high evapotranspiration rates resultingin reduced ambient temperature of the surroundingarea in summer, and in lateral heat emissionfrom the water body in winter. Rice can be usedas a desalinization crop because the continuouslypercolating water (Chapter 1.3) leaches salts fromthe topsoil (Bhumbla and Abrol 1978). The leachateshould be removed by a good drainage system, orelse there is risk for increased salinization of thegroundwater. Rice soils that are flooded for longperiods of the year contribute to the mitigation ofthe greenhouse effect by taking CO 2from the atmosphereand sequestering the carbon (C) (Bronson1997a, Dobermann 2003).As a supporting service, flooded rice fields andirrigation channels form a comprehensive waternetwork, which, together with the contiguous dryland, provides a complex mosaic of landscapes. Irrigatedrice land has been classified as human-madewetlands by the Ramsar Convention on Wetlands(Ramsar 2004). Surveys show that such landscapessustain a rich biodiversity, including unique aswell as threatened species, and also enhance biodiversityin urban and peri-urban areas (Fernandoet al 2005).The cultural services of rice fields are especiallyvalued in Asian countries where, for centuries,rice has been the main staple food and thesingle most important source of employment andincome for rural people. Many old kingdoms aswell as small communities have been founded onthe construction of irrigation facilities to stabilizerice production. Rice affects daily life in many waysand the social concept of rice culture gives meaningto rice beyond its role as an item of production and35
consumption (Hamilton 2003). Many traditionalfestivals and religious practices are associated withrice cultivation and rice fields are valued for theirscenic beauty.4.2 Environmental impactsThe production of lowland rice affects the environmentin negative ways, such as the emissionof greenhouse gases and water pollution. In thissection, environmental impacts that have a relationshipwith water and the hydrology of rice fields aresummarized.4.2.1 Ammonia volatilizationAmmonia (NH 3) volatilization from urea fertilizeris the major pathway of N loss in tropical floodedrice fields, often causing losses of 50% or more ofthe applied urea-N (Buresh and De Datta 1990).Ammonia-N emissions from lowland rice fields areestimated to be roughly 3.6 Tg per year (comparedwith a total of 9 Tg y −1 emitted from all agriculturalfields), which is some 5−8% of the estimated 45−75Tg of globally emitted ammonia-N per year (Kirk2004). The magnitude of ammonia volatilizationlargely depends on climatic conditions, field waterstatus, and the method of N fertilizer application.Volatilized ammonium can be deposited on theearth by rain, which can lead to soil acidification(Kirk 2004) and unintended N inputs into naturalecosystems.4.2.2 Greenhouse gasesIrrigated rice systems are a significant sink for atmosphericCO 2(Chapter 4.1), a significant sourceof methane (CH 4), and a small source of nitrousoxide (N 2O). In the early 1980s, it was estimatedthat lowland rice fields emitted some 50−100 Tgof methane per year, or about 10−20% of the thenestimated global methane emissions (Kirk 2004).Recent measurements, however, show that manyrice fields emit substantially less than those investigatedin the early 1980s, especially in northern Indiaand China. Also, methane emissions have actuallydecreased since the early 1980s because of changesin crop management such as a decreased use oforganic inputs (Van der Gon et al 2000). Currentestimates of annual methane emissions from ricefields are in the range of 20 to 60 Tg, being 5–10%of total global emissions of about 600 Tg (Kirk2004). The magnitude of methane emissions fromrice fields is mainly determined by water regime andorganic inputs, and to a lesser extent by soil type,weather, tillage, residue management, fertilizer use,and rice cultivar (Bronson et al 1997a,b, Wassmannet al 2000). Flooding of the soil is a prerequisitefor sustained emissions of methane. Mid-seasondrainage, a common irrigation practice adopted inmajor rice-growing regions in China and Japan,greatly reduces methane emissions. Similarly,rice environments with an uneven supply of water(for example, those suffering from water scarcity,Chapter 1.7) have a lower emission potential thanfully irrigated rice.Few accurate assessments have been made ofemissions of nitrous oxide from rice fields (Abao etal 2000, Bronson et al 1997a,b, Dittert et al 2002),and the contribution to global emissions has not yetbeen assessed. In irrigated rice systems with goodwater control, nitrous oxide emissions are quitesmall except when excessively high fertilizer-Nrates are applied. In irrigated rice fields, nitrousoxide emissions mainly occur during fallow periodsand immediately after flooding of the soil at the endof the fallow period.4.2.3 Water pollutionChanges in water quality associated with rice productionmay be positive or negative, dependingmainly on management practices such as fertilizationand biocide (all chemicals used for crop protection,such as herbicides, pesticides, fungicides, etc.)use. The quality of the water leaving rice fields maybe improved as a result of the capacity of the ricefields to remove nitrogen and phosphorus (Feng etal 2004, Ikeda and Watanabe 2002). On the otherhand, nitrogen transfer from flooded rice fields bydirect flow of dissolved nitrogen through runoffwarrants more attention. High nitrogen pollutionof surface fresh waters can be found in rice-growingregions where fertilizer rates are excessivelyhigh, such as in Jiangsu Province in China (Cuiet al 2000).Contamination of groundwater may arisefrom the leaching of nitrate or biocides and theirresidues (Bouman et al 2002). Nitrate leachingfrom flooded rice fields is quite negligible becauseof rapid denitrification under anaerobic conditions(Buresh and De Datta 1990). For example, in thePhilippines, nitrate pollution of groundwater underrice-based cropping systems surpassed the 10 mgL −1 limit for safe drinking water only when highly36
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 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

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