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

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Ψ Air–100 MPaDemandLeafXylemStemRootStomatal cavityΨ Leafг StemΨ Rootг Leaf–1 MPa–0.4 MPaWater phase Vapor phaseEndodermisг RootSupplyWater flowSoil particleΨ Soil–0.02–0.1 MPaΨroot – Ψsoil Ψleaf – Ψroot Ψair – Ψleaf= =гroot гstem гleafFig. 2.2 Schematic overview of water flow and water potentials in the soil-plant-atmosphere continuum. Adapted fromLövenstein et al (1992).Table 2.2. Some typical soil water tension levels in relation to the growth of upland crops (e.g., wheat, maize, cotton).Name pF value ExplanationSaturation –∞ All soil pores are filled with waterField capacity 2 Soil water content that is considered optimum for upland cropsPermanent wilting point 4.2 Soil water content at which most upland crops cannot extractwater from the soil any more and show permanent wiltingAir dryness 7 No free water in soil pores any moreavailability, soil microbial population, soil organicmatter buildup/decomposition, and occurrence ofsoil pests and diseases (Chapter 3.6). Figure 2.3illustrates soil water tensions measured in an aerobicsoil where rice was grown under nonfloodedconditions like an upland crop.Each soil has a specific relationship betweenthe tension of the water and the amount of water:the lower the amount, the higher the tension. Thus,a small amount of water in the soil and a hightension both reflect a condition of relative “waterscarcity” and drought. The relationship betweensoil water tension and soil water content is calledthe “soil water retention curve” or the “pF curve.”The shape of the pF curve depends on soil type,especially on its texture (mixture of clay, silt, andsand particles), bulk density (the weight of a soilover its volume), mineralogy, and organic mattercontent. Examples are given in Figure 2.4 for atypical clay soil and a typical sand soil. There arefour important points on the pF curve for uplandcrops: saturation = pF –∞ (H = 0 cm), field capacity= pF 2, permanent wilting point = pF 4.2, andair dryness = pF 7 (see Table 2.2). The amount ofwater at each of these four tensions is different foreach soil type. When rice fields are flooded, thepF curve is not needed as soil water contents arealways at saturation. However, when a rice soil13
Soil moisture tension (kPa)100908070605040302010PanicleinitiationFloweringHarvest0175 200 225 250 275 300Day numberFig. 2.3. Time course of soil water tension in the root zone of rice grown in a nonpuddled, nonflooded soil (this system iscalled “aerobic rice,” Chapter 3.4). The dips in tension are associated with rainfall or an irrigation event. Adapted from YangXiaoguang et al (2005).Air dryness (pF 7)Soil water tension (pF = log(–H))765ClayPermanent wilting point (pF 4.2)43SandField capacity (pF 2)21Saturation (pF –∞)00 0.1 0.2 0.3 0.4 0.5 0.6Soil water content (cm 3 cm –3 )Fig. 2.4. Typical soil water retention curve (or pF curve) for a clay soil and a sand soil. Notice the differences in water contentat the four critical tension levels (Table 2.2) for the two soil types. Adapted from Lövenstein et al (1992).becomes dry, the pF curve becomes meaningful asit indicates the amount of water available for plantuptake at different tensions.2.2 The rice plant and droughtCultivated rice evolved from a semiaquatic perennialancestor (Lafitte and Bennett 2002). Thewetland ancestry of rice is reflected in a number ofmorphological and physiological characteristicsthat are unique among crop species. Lowland riceis extremely sensitive to water shortage and droughteffects occur when soil water contents drop belowsaturation. Rice has a variety of mechanisms bywhich it reacts to such conditions. The following isa list compiled by Bouman and Tuong (2001):1. Inhibition of leaf production and decline inleaf area, leading to retarded leaf growthand light interception, and hence to reducedcanopy photosynthesis. Drought stress affectsboth cell division and enlargement,though cell division appears to be less sensi-14
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 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

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