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

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Table 3.8. Comparison of water use <strong>in</strong> a hypothetical aerobic <strong>rice</strong> crop with that of lowland <strong>rice</strong> on different soil typescharacterized by their seepage (S) and percolation (P) rates.<strong>Water</strong> flow process Aerobic <strong>rice</strong> (mm) Lowland <strong>rice</strong> (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 <strong>in</strong>efficiency loss 90 335 − − −Total 590 835 700 1,100 2,100Yield (t ha –1 )10987654321AerobicFlooded0200 400 600 800 1,000 1,200 1,400<strong>Water</strong> <strong>in</strong>put (mm)Fig. 3.7. Yield of aerobic <strong>rice</strong> varieties HD297 ( ) and HD502 ( ) and lowland <strong>rice</strong> variety JD305 ( ) at different levels ofwater <strong>in</strong>put. Data from Yang Xiaoguang et al (2005).higher yields than flooded lowland <strong>rice</strong> is given <strong>in</strong>Figure 3.7 for field experiments at Beij<strong>in</strong>g <strong>in</strong> Ch<strong>in</strong>a(Yang Xiaoguang et al 2005). Two aerobic <strong>rice</strong>varieties (HD297 and HD502) and one lowland <strong>rice</strong>variety (JD305) were grown under flooded conditionsand under aerobic soil conditions with differentamounts of total water <strong>in</strong>put. Under floodedconditions with 1,300−1,400 mm of water <strong>in</strong>put 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, quicklydecl<strong>in</strong>ed with <strong>in</strong>creas<strong>in</strong>g water shortage and aerobicsoil conditions. With less than 1,100 mm of water<strong>in</strong>put, and under aerobic soil conditions, aerobic<strong>rice</strong> varieties HD297 and HD502 outperformed thelowland variety.When water is physically available, but has ahigh cost, the choice of adopt<strong>in</strong>g any of the watersav<strong>in</strong>gtechnologies becomes more of an economicissue. Adopt<strong>in</strong>g certa<strong>in</strong> water-sav<strong>in</strong>g technologiesmay reduce water but at the expense of yield loss.If the f<strong>in</strong>ancial sav<strong>in</strong>gs <strong>in</strong>curred by us<strong>in</strong>g less irrigationwater under a certa<strong>in</strong> technology outweigh thef<strong>in</strong>ancial loss of reduced yield, then the adoptionof that technology becomes attractive. Figure 3.8gives so-called “water-response curves” obta<strong>in</strong>edfrom two different field experiments <strong>in</strong> India wheredifferent forms of AWD were implemented (different<strong>in</strong>tervals between irrigations). The experimentof the lower curve was done <strong>in</strong> Cuttack, Orissa(Jha et al 1981). The climatic yield potential wasrelatively low s<strong>in</strong>ce the experiment was performed31

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