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

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Table 5.1. Area, water use, and total production of flooded rice and of rice grown under AWD, in ahypothetical irrigation scheme of 10,000 ha with 134 10 6 m 3 of water available.Land use Area (ha) Water use (10 6 m 3 ) Production (tons)Scenario I (80% farmers, flooded rice; 20% farmers, no crop)Flooded 8,000 134 46,400AWD 0 0 0Fallow 2,000 0 0Sum 10,000 134 46,400Scenario II (65% of farmers, flooded rice; 35% farmers, AWD)Flooded 6,560 110 38,048AWD 3,440 24 14,852Fallow 0 0 0Sum 10,000 134 52,900Table 5.2. Yield, water productivity with respect to total water input (WP IR), and water input of floodedrice and rice grown under AWD (from Table 3.2, Guimba 1989).Yield (t ha −1 ) WP IR(kg m −3 ) Water use (m 3 ha −1 )Flooded 5.8 0.345 1,679AWD 4.3 0.614 700Table 5.3. Area under rice production, and total water use, rice production, and number of farmers,with flooded rice and with AWD as design criteria.Design criterionRice area Water use Production Farmers(ha) (10 6 m 3 ) (tons) (number)Flooded 10,000 168 58,000 10,000AWD 23,986 168 103,000 23,986but illustrates the effect of including the conceptof water productivity (besides yield) in irrigationsystem management.5.5 Irrigation system designAWD irrigation can be taken as a starting point inthe design of a new irrigation system. Suppose thata hypothetical reservoir can be constructed with acapacity of 168 10 6 m 3 , and that a command areawill be designed for rice farmers getting 1 ha each.If AWD irrigation is the design criterion ratherthan flooded rice, the irrigated rice area and totalrice production are larger, and more farmers willbenefit from irrigation development (Table 5.3).If reuse of percolation and drainage water is takeninto consideration in the design, the rice area underirrigation can increase further in both scenarios.With 100% reuse of water, the irrigated rice areaswould be similar in both scenarios since AWDmostly saves water by reducing percolation flows(that can be reused) and only a little by reducingevaporation (which cannot be reduced). However,100% water reuse is in practice not attainable andthe implementation of AWD would lead to thelargest area under irrigation.This example demonstrates the impact thatwater-saving technologies can have on irrigationsystem design. Rather than taking continuous floodingof fields as a design criterion, a rotation of waterdelivery can be used that is designed to let the fieldsdry out for a few days during each rotation cycle.43
Field water requirements during the flooded daysshould be based on evapotranspiration, seepage, andpercolation, whereas, during the nonflooded days,they can be based on evapotranspiration alone.A system can also be designed to maximizethe reuse of seepage and percolation water as muchas possible through check dams and pumping. Ifthere is a salinization hazard, care should be takento avoid using water that has become too saline byreuse through judicious mixing of drainage andfresh water.Construction of field channels (irrigation,drainage) and land leveling should be considered tofacilitate good water management. Farmers in a newirrigation system should be trained in sound watermanagement practices such as those detailed in thismanual (bund maintenance, crack plowing, etc.).44
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 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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