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

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Appendix: InstrumentationDetailed descriptions and user guides of equipmentto measure water flows and soil physical andhydrological properties of rice soils are given byIRRI (1987) and Wopereis et al (1994). Calculationand measurement procedures for evapotranspirationare given by FAO (1998). Here, we introduce twosimple tools that are practical in characterizing thewater status (hydrological conditions) of rice fieldsand can help guide the implementation of watersavingtechnologies.A.1 Field water tubeThe field water tube is used to measure the depth ofstanding water on the field, be it on top of the surfaceor just below the surface (Fig. A.1). PerforateWith standing wateron top of the surface:read this20-cm-diameter PVC pipeUse a ruler tomeasure water depth15 cmSoil surfacePuddledtopsoil20 cmWith water belowthe soil surface:read thisPlow panHoles are 5 mm in diameter,and spaced 2 cm apartFig. A.1. Field water tube for monitoring the depth of standing water on a rice field.45
Fig. A.2. Groundwatertube for monitoringgroundwater depth belowrice fields.Cover(used tin can)5-cm-diameter PVCpipeBund surface50 cmReadhere100 cm 200 cmMeasuringdeviceGroundwater levelHoles are 5 mmin diameter, 2 cm apart50 cma hollow and bottomless PVC-tube of about 20 cmin diameter and 35 cm long with small holes using adrill. The holes should be about 0.5 cm in diameterand spaced 2 cm apart. Install this tube in the fieldso that the bottom of the tube is buried in the plowsole (about 20 cm deep) and that some 15 cm ofthe tube protrudes above the soil surface. Removethe soil from inside the tube down to the bottom ofthe tube. Water will flow through the holes into thetube, so that the water level inside the tube is thesame as outside. After irrigation, the level of thewater in the tube can be seen going down every day.The tube can be placed at the side of the field closeto the bund (but at least 1 m away from the bund),so it is easy to record the water depth (no need towalk very deep into the field). Make sure that thespot chosen to install the tube is representative forthe whole field (don’t place it in a depression or inan elevated patch).The water depth is measured from the top ofthe tube to the level of the water in the field usinga simple ruler. Subtract 15 cm from the reading toobtain the depth of ponded water. A negative valuemeans that the water is standing on the field; a positivevalue means that the water level is below thesurface. To make the measurement more accurate,the height of the tube protruding above the surfacecan be measured a few times during the season tocheck whether it is 15 cm.A.2 Groundwater tubeThe groundwater tube is used to measure the depthof the groundwater below the rice fields (Fig. A.2).Cut a length of 175 to 250 cm of hollow and bottomlessPVC-tube of about 5 cm in diameter. Use adrill to make holes along a section of 50-cm lengthat one end of the tube. The holes should be about46
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 46 and 47: the main system is supply-driven, f
Page 48 and 49: Table 5.1. Area, water use, and tot
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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