GCP 2011 General Research Meeting

21-25 September,2011

Hyderabad, India

Characterization of drought-prone

rainfed rice ecosystems of

the Mekong Region

Inthavong, T., Linwattana, G., Touch, V.,

Pantuwan, G, Jongdee, B., Mitchell,

J.H., and Fukai, S.

(NAFRI, BRRD, CARDI, UQ)

Objectives

1. Development of Soil Water Balance Model

and use it for quantifying field water

availability during the growing season

2. Identify the spatial pattern of drought prone

areas in the Mekong Region.

3. Estimation of yield reduction by water stress

4. Conclusions

Rainfed lowland rice production area

Large areas of rainfed lowland areas with drought-prone and drought- & submergence-prone environments in the Mekong region

65% of total rice land in Cambodia, 44% in Laos, 56% in Thailand

% Irrigated Rainfed lowland Upland Deepwater

Total F D DS S MD

Cambodia 16 75 7 22 43 0 3 1 8

Indonesia 54 35 20 4 0 3 8 11 0

Laos 14 65 22 22 22 0 0 21 0

Malaysia 66 21 15 0 0 5 1 12 1

Myanmar 30 59 24 6 0 15 14 4 7

Philippines 67 30 15 5 1 3 6 3 0

Thailand 20 74 6 38 18 9 3 2 4

Vietnam 53 39 15 8 0 12 4 5 3 F: favorable, D: drought-prone, DS: drought- and submergence-prone, S: submergence-prone, MD: medium-deep

Source: Mackill et al. (1996), IRRI (2005)

Rainfall distribution

(i) uncertainty in the onset of the rainy season that can affect

timely sowing and transplanting.

(ii) late season drought affects on reproductive stage of

plant growth and development.

• Coarse soils

CL (4.5%)LL (11.5%)

SL (38.1%)

LS (41.3%)

SA (4.5%)

Proportion of % soil texture types distributed throughout

the Savannakhet province

Soil characteristics

Top paddy

Middle paddy

Bottom paddy Groundwater

table/head Downward movement

Lateral movement

Groundwater flow

Runoff (catchment)

Toposequence

» A sequence of

paddy fields on

slopping land

Development and use of a soil water balance

model (SWB) for quantifying:

weekly rice field water storage

spatial variation in field water availability

water stress development during rice growing

period

Rainfall Transpiration

Evaporation

Runoff

Seepage

Under-bund Percolation

Lateral movement Downward movement

Quantifying water balance components

Surface layer

D

Subsoil layer

DP

bund

Surface soil water content (Wsurface)

within 0 - 20cm

Subsoil water content (Wsubsoil) between 20 -

100cm where Dsubsoil equals to deep

percolation (DP)

The total amount of water storage in two

layers (surface + subsoil)

+

=

Development of a 2-layer soil water balance model

Lateral water

movement

Quantifying

downward water

movement (D)

Groundwater

tube

Perched water

tube

Percolator

Percolation on different soils (clay content)

Large variation in percolation across locations could be

explained by clay content of the soil.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 10 20 30 40 50

Dow

nw

ard

wate

r f

low

(m

m/d

ay)

Clay content (%)

D= 18.7/clay -0.16 (r=0.67) D measured from

NEThailand

D predicted for

these three regions

D measured from

southern Laos

D measured from

CARDI (Cambodia)

When there is standing water in the field.

When field water storage decrease from soil Saturate to FC

When there is no standing water, there is no downwater loss.

Generate climate input

Spatial interpolation function in GIS (Variography and kriging) Rainfall data (1985-2008) 325 met and hydrological stations: 33 met. and 10 hydro. Stations (Laos) 169 met. (North and North-East Thailand) 94 stations (Cambodia)

- Rainfall

- Crop Evapotranspiration (ETc)

Thailand

Laos

Cambodia

Crop Evapotranspiration (ETc)

ocsc ETKKET

2

2

34.01

273

900408.0

U

eeUT

GR

ETdan

o

airdryWFCW

airdryWsurface

sSS

SWK

__

_

+ Crop coefficient (Kc)

(Initial stage Kc=1.05,development stage Kc=1.2,

late season stage Kc=0.6-0.9) (Allen et al.,1998)

+Water stress coefficient (Ks)

+ Reference Evapotranspiration (ETo)

Potential evapotranspiration (Penman-Monteith equation)

Week 15 Week 25

Week 35 Week 40

Soil profile samples

Schematic diagram for quantifying free water level and water stress

development based on lowland water balance model

Soil data

Clay

% Downward

(D)

Climate data

Rainfall ETc

FIELD WATER BALANCE MODEL: W(t)= W(t-1)+RF(t)-ETc(t)–D(t)-L(t)-R(t)

Determination of LGP, SGP, EGP

Daily free water level

Estimation probability of drought occurrence

Sat, FC,

WP, Air (Saxton & Rawls)

•Point based (daily)

•Gridded surface

(weekly)

Soil water balance model for quantifying LGP

Duration for the length of growing period (LGP)

Start of growing period (SGP) End of growing period (EGP

The prediction of water availability can be

made with weather forecasting

Weather Forecast Division

Department of

Meteorology and

Hydrology

050

100150200250300350400450500550

1 2 3 4 5 6 7 8 9 10 11 12

Months

mm

20002001200220032004Mean

Results of weekly water availability prediction

made at two different times in 2010.

Forecast standing water level for

week 28 (9-15 July 2010)

Forecast standing water level for

week 41 (8-14 Oct 2010)

0

10

20

30

40

50

60

70

80

90

100

-40 -35 -30 -25 -20 -15 -10 -5 0

Ralative water level (cm)

Gra

in y

ield

red

ucti

on

(%

)

Early

Medium

Late

Y = -1.68X; r2 = 0.80

Linear (Y = -1.68X; r2

= 0.80)

Y=-1.68X; r2 =0.80 (cm)1.68WL- (%)reduction Yield Rel

-100.00

-50.00

0.00

50.00

100.00

150.00

200.00

250.00

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

Weeks

mm

Rainfall Depth of standing water Field water storage

Soil water at FC Soil water at WP

StartLGP wk19 End LGP wk41Flowering

Khanthaboury (wet

season rice, 1988)

Estimation of Yield limited by water stress

• Water stress around

flowering (3 week

before and after)

Ouk et al.,(2006)

Start LGP End LGP LGP Flowering date Wlrel(mm) %yield reduction

19 43

25 17-Sep -74.1 12

Using SWB in conjunction with GIS can provide:

a geographical dimension of soil hydrological patterns for

various rice growing environments.

identify the spatial pattern of drought stress that is likely to

occur from long term climate data.

identify strategies for plant breeding and geographical targeting

of improved varieties with particular drought tolerance or

drought avoidance characteristics.

To provide guidelines for practical advice to the rice farmers

and researchers for the determination of appropriate crop

management strategies (e.g. time of planting, selection of

varieties) and policy makers for investment decisions.

Conclusion

THANK YOU!