Rice and water. Crop and Environmental Sciences Division International Rice Research Institute Los Baños, Philippines

Transcription

1 Rice and water Crop and Environmental Sciences Division International Rice Research Institute Los Baños, Philippines

2 Irrigated rice and water 95% of the world s rice is produced in Asia 75% of rice produced is irrigated (75 m ha) Irrigation in developing countries: uses 80-90% of fresh water developed In Asia: > 50% of this is for rice Rice requires much water: l kg-1 rice Rice receives 34-43% of world s irrigation water Rice receives 24-30% of world s developed fresh water Rice is biggest single user of developed fresh water

3 106 ha World irrigated area World irrigated rice area Asia irrigated area

4 km World water withdrawal Rice water use in irrigation World water use in irrigation

5 Why does rice require so much water?

6 Field water balance lowland rice

7 Computing water balance Input outputs = storage change Neglect storage change: Inputs = outputs Measure (weir, flume, flow meter) Rest term Irrigation + rainfall = seepage & percolation + evapotranspiration Measure (rain gauge) Calculate (Penman, pan evaporation)

8 Water requirements in lowland rice Daily (mm d-1) Season (100 d) Land preparation Evapotranspiration Wet season Dry season Seepage & percolation Heavy clay Loamy sand Total season Typical value (30-40% evaporation) : mm : mm

9 Examples water use; China ZIS (Wuhan) Experiment Farmers Mezo site Shimen (HZ) Early Late Water (mm) SP (mm d-1) (3.8) (3.8)

10 Examples water use; Philippines Water (mm) Guimba Muñoz Talavera San Jose San Jose (DS) (DS) PhilRice SP (mm d-1) (-> 4.4)

11 Groundwater: a hidden source of water Groundwater depth (cm) 20 (cm) 20 0 Groundwater depth (cm) Day number Panicle initiation Flow ering Harvest Day number Tuanlin, China, Changle, China, 2002 Groundwater depth (cm) Direct uptake of water by plant roots Dolores, Philipines,

12 Where do the outflows go? Evaporation and transpiration: unrecoverable Overbund flow, seepage, percolation: reusable Pokhara, Nepal, 2006

13 Surface and subsurface water flows across a toposequence of rice fields. D = drainage (over-bund flow); I = irrigation, P = percolation; S = seepage.

14 Water re-use through reservoirs and on-farm ponds Z H A N G H E MAP OF WENJIAXIANG SITE IN CHINA I R R I G A T I O N D I S T R I C T N g an Zh r e Riv Ju Rive r Zhongxiang Ci ty The Fourt h Mai n Canal * We njiaxi ang Ji nmen City ing Hanj * r Rive The Main West Cana l Zhanghe Reservoir General Ma in Canal The Mai n Second Can al * Tuan lin ird l Th an a e T h in C Ma The First Main Canal Zhanghe Project Administration Dangyang Ci ty * Ri Juzhang Shayang Ci ty ve r Zhi jian g Ci ty Roads Drainage Canals Changhu Lake Ji angl in City Irrigation Canals Boundary Shashi Ci ty GPS Meas urements points Tanks Yangtze River Railway track Roads Main Ir rigation canals Irrigation canals Dr ainage canals Natiral streams Cities River s Reservoirs IW MI - J ANU A RY So ur ce : Z ha ng he P ro ject Adm inis tra tio n De ce mb er N Designed Ir rigated ar ea Catchment area reservoir Area with supplementary Irr igation, prone to flooding

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16 UPRIIS irrigation scheme, Philippines District I: 18,000 ha Increased production with increase in scale, using same amount of irrigation Water re-use by pumps: 18% farmers 23% area 10% water reused Reuse surface water by small dams 45% water reused

17 Water reuse (106 m 3) y = x R = y = x R = Area (ha) Water reuse by check dams in creeks/drains ( ) and by pumping from shallow groundwater ( ) District I, UPRIIS, Philippines, 2002

18 Water productivity (WP) Amount of grain produced per unit of water used kg grain m-3 water What water used? WPT WPET WPI WPIR : water transpired : water lost by evapotranspiration : water put in by irrigation : water put in by irrigation and rainfall Start counting water at land preparation or at crop establishment

19 Water productivity (WP) Water productivity (kg grain m-3 water) Rice Dryland cereal Per transpiration (T) 1 up to 2 wheat: up to 2 Per evapotranspiration (ET) (1.1) wheat: maize: Per inputs by rain and irrigation (RI) (0.4) : measured in pots 2 : measured in fields 1

20 Frequency (%) 30 Zwart and Bastiaans, WPET 0 Frequency (%) Tuong, Bouman, Mortimer, WPIR 0

21 Some conclusions Rice plant same WPT as other C3 cereals Rice field same WPET as other C3 cereals Variation in WPET caused by variety, climate, management Rice field requires 2-3 times more water than other cereals, mainly because percolation and seepage losses (25-50% in heavy soil with shallow groundwater, to 50-85% in lighter soils with deep groundwater) Percolation and seepage are/can be reused downstream

22 Pressure to produce more food (rice) is getting greater because of ever increasing population But also: More people want more industry more drinking water more cities more swimming pools more. => Water is getting scarce and expensive

23 Need to develop technologies to help farmers cope with water shortage (ie, not enough water to keep rice fields continuously flooded) Water-saving technologies