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Table 3.8. Comparison of water use in a hypothetical aerobic rice crop with that of lowland rice on different soil typescharacterized by their seepage (S) and percolation (P) rates.Water flow process Aerobic rice (mm) Lowland rice (mm)Lowland soil SP rate − − 1 mm d −1 5 mm d −1 15 mm d −1Irrigation efficiency 85% 60% − − −Evaporation 100 100 200 200 200Transpiration 400 400 400 400 400Seepage and percolation − − 100 500 1,500Irrigation inefficiency loss 90 335 − − −Total 590 835 700 1,100 2,100Yield (t ha –1 )10987654321AerobicFlooded0200 400 600 800 1,000 1,200 1,400Water input (mm)Fig. 3.7. Yield of aerobic rice varieties HD297 ( ) and HD502 ( ) and lowland rice variety JD305 ( ) at different levels ofwater input. Data from Yang Xiaoguang et al (2005).higher yields than flooded lowland rice is given inFigure 3.7 for field experiments at Beijing in China(Yang Xiaoguang et al 2005). Two aerobic ricevarieties (HD297 and HD502) and one lowland ricevariety (JD305) were grown under flooded conditionsand under aerobic soil conditions with differentamounts of total water input. Under floodedconditions with 1,300−1,400 mm of water input tothe right-hand side of the horizontal (water) axis,lowland variety JD305 gave the highest yields of8−9 t ha −1 . The yield of JD305, however, quicklydeclined with increasing water shortage and aerobicsoil conditions. With less than 1,100 mm of waterinput, and under aerobic soil conditions, aerobicrice varieties HD297 and HD502 outperformed thelowland variety.When water is physically available, but has ahigh cost, the choice of adopting any of the watersavingtechnologies becomes more of an economicissue. Adopting certain water-saving technologiesmay reduce water but at the expense of yield loss.If the financial savings incurred by using less irrigationwater under a certain technology outweigh thefinancial loss of reduced yield, then the adoptionof that technology becomes attractive. Figure 3.8gives so-called “water-response curves” obtainedfrom two different field experiments in India wheredifferent forms of AWD were implemented (differentintervals between irrigations). The experimentof the lower curve was done in Cuttack, Orissa(Jha et al 1981). The climatic yield potential wasrelatively low since the experiment was performed31
Yield (t ha –1 )864200 500 1,000 1,500 2,000 2,500 3,000Water input (mm)Fig. 3.8. Yield versus water input in two experiments in India. Top curve data ( ) are from Pantnagar, Uttar Pradesh (Tripathiet al 1986), and bottom curve data ( ) are from Cuttack, Orissa (Jha et al 1981). The curved lines are fitted productionfunctions of the shape [yield = a*(1 – e (b*(water input – c)) )]. Adapted from Bouman and Tuong (2001).in the winter season (low radiation levels). Fertilizerapplication was only 80 kg N ha −1 and zero Pand K. The soil SP rate was about 21 mm d −1 . Theexperiment of the top curve was done in Pantnagar,Uttar Pradesh (Tripathi et al 1986). The climaticyield potential was higher because the experimentwas done in the summer (high radiation levels). Torealize the higher yield potential, fertilizer applicationswere also higher: 120 kg N ha −1 , 60 kg P 2O 5ha −1 , and 40 kg K 2O ha −1 . The soil SP rate was 9−14mm d −1 . Going from right to left on the horizontalaxis, water use decreased with adopting increasingintervals between irrigations in AWD. Yieldswere initially not affected, but, after a certain point,yields declined with less water use. This happenedsomewhere below 1,750 mm for the top curveand somewhere below 1,000 mm for the bottomcurve. This example illustrates the site-specificityof results of AWD. Farmers will decide on thetype/severity of AWD to adopt based on the sitespecificfinancial trade-off between yield declineand water savings.3.6 SustainabilityWhile relatively much work has been done onthe development of technologies to maintain cropproductivity under water scarcity, little researchhas been done on their long-term sustainability andenvironmental impacts. Given assured water supply,lowland rice fields are extremely sustainableand able to produce continuously high yields, evenunder continuous double or triple cropping eachyear (Dawe et al 2000). Flooding of rice fields hasbeneficial effects on soil acidity (pH); soil organicmatter buildup; phosphorus, iron, and zinc availability;and biological N fixation that supplies thecrop with additional N (Kirk 2004). When fieldscannot be continuously flooded any more becauseof water scarcity, these beneficial effects graduallydisappear. A change to more aerobic soil conditions(such as in AWD and aerobic rice) will negativelyaffect the soil pH in some situations and decreasethe availability of phosphorus, iron, and zinc. Underthe “safe AWD” practice (Chapter 3.3.2), theseproblems do not occur, but, when more severe formsof AWD are implemented, they may start to occur.Under fully aerobic conditions, whether on flat landor on raised beds, problems with micronutrientdeficiencies have been reported by Choudhury etal (2007), Sharma et al (2002), Singh et al (2002),and Tao Hongbin et al. (2006). The introductionof aerobic phases in rice fields may also decreasethe soil organic carbon content. In a long-term experimentat IRRI, where a continuous rice systemis compared with a maize-rice system, 12 yearsof maize-rice cropping caused a 15% decline insoil organic C and indigenous N supply relative to32
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 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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