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

Table 3.4. Water input (I = irrigation R = rainfall) and yield of two aerobic rice varieties (HD502, HD297) under flooded andaerobic conditions in 2001 and 2002, Beijing, China. Data from Yang Xiaoguang et al (2005).YearWater Water input (mm) Yield (t ha −1 )managementI I + R HD502 HD2972001 Flooded 1,057 1,351 6.8 5.4aerobic 350 644 5.3 4.7283 577 4.6 4.3292 586 4.3 4.2225 519 3.5 3.4175 469 3.0 2.52002 Flooded 900 1,255 4.6 5.3aerobic 522 917 5.7 5.3374 769 4.8 4.7225 620 4.0 3.9300 695 4.3 4.6152 547 3.6 2.9upland crop, such as wheat or maize. Unlike lowlandrice, upland crops are grown in nonpuddled,nonsaturated (i.e., “aerobic”) soil without pondedwater. When rainfall is insufficient, irrigation is appliedto bring the soil water content in the root zoneup to field capacity after it has reached a certainlower threshold level, such as halfway between fieldcapacity and wilting point (Doorenbos and Pruit1984). The amount of irrigation water should matchevaporation from the soil and transpiration by thecrop (plus any application inefficiency losses). Thepotential water reductions at the field level whenrice can be grown as an upland crop are large, especiallyon soils with high seepage and percolationrates (Bouman 2001; Chapter 3.5). Besides seepageand percolation losses declining, evaporation decreasessince there is no ponded water layer, and thelarge amount of water used for wet land preparationis eliminated altogether (Chapter 3.1.3).In Asia, “upland rice” is already grown aerobicallywith minimal inputs in the upland environment,but mostly as a low-yielding subsistence cropto give stable yields under the adverse environmentalconditions of the uplands (Lafitte et al 2002).Upland rice varieties are drought tolerant, but havea low yield potential and tend to lodge under highlevels of external inputs such as fertilizer and supplementalirrigation. Alternatively, high-yieldinglowland rice varieties grown under aerobic soilconditions, but with supplemental irrigation, havebeen shown to save water, but at a severe yieldpenalty (Blackwell et al 1985, Westcott and Vines1986, McCauley 1990). Achieving high yieldsunder irrigated but aerobic soil conditions requiresnew varieties of “aerobic rice” that combine thedrought-tolerant characteristics of upland varietieswith the high-yielding characteristics of lowlandvarieties (Lafitte et al 2002, Atlin et al 2006).The development of temperate aerobic ricestarted in the mid-eighties in northern China andBrazil. In China, breeders have produced aerobicrice varieties with an estimated yield potential of6-7 t ha –1 (Wang Huaqi et al 2002). In experimentswith Chinese aerobic rice varieties close to Beijingin 2001 and 2002, Yang Xiaoguang et al (2005) andBouman et al (2006b) obtained aerobic rice yieldsof 2.5−5.7 t ha −1 with only 500−900 mm of total(irrigation plus rainfall) water input (Table 3.4). Forcomparison, the aerobic varieties yielded 5.4−6.8t ha −1 under flooded lowland conditions, receivingabout 1,300 mm of total water input. At the samesite, Xue et al (2007) reported yield maxima of3.6−4.5 t ha −1 with 688 mm of total water input in2003, and 6.0 t ha −1 with 705 mm of water inputin 2004 (Table 3.5). The relatively high yields ofaerobic rice at Beijing were obtained under “harsh”conditions for growing rice. The soil containedmore than 80% sand, was permeable, and heldwater above field capacity for a few hours afterirrigation only. The groundwater table was deeperthan 20 m, the soil moisture content in the root zonewas mostly between 50% and 80% of saturation,and soil moisture tensions went up to 90 kPa (seeFig. 2.3 in Chapter 2.1). In field experiments near24