Future concerns about rice production
in relation to water
Koki Homma
Graduate School of Agricultural Science,Tohoku UniversityIn Japan, decrease of 1st graded rice percentage
has remarkable occurred due to globalwarming.
Temperature in the major rice productionseason in Japan is not necessarily lower thanthat in Southeast Asia.
NormalChalky grain

Temperature degree CGlobal warming impacts on rice production
454035
30
2520
15
10
50-5Max.. and min. air temp. Mean +- SD for a 27yr.

Kyoto(MAFF)

Temperature degree C

1st graded rice (%)

10080604020454035302520
151050■Nagasaki◆Fukuoka

01970

Max. and min. temp. Mean +- SD

1990

2010

Khonkaen, Thailand

Global warming impacts on rice production
The simulation study also suggested that the rice productivity
in southwestern Japan will be reduced.
No breakthrough method has been found to break thissimulated results.
Only the effect of a few ˚C difference is quite difficult toexperimentally clarify.
Counter measures of late-planting, fertilizer treatment, water
management and so on are tested besides breeding of newvarieties.

The global warming is the common issue
in rice production in Asia.
Adaptation of crop management is firstly required.
However, water management which is one of the mostimportant management in rice production has not been wellinvestigated under future climate condition.

Koshihikari, present+4˚C [CO2] = 525 ppm
can be cultivatedfurther northwill be reduced
in southwesternClimate (precipitation) change impacts on rice production
Combined crop simulation model with hydrological model

Irrigation

Crop (fertilizer,planting)Management

Leaf area index

Water circulation

Rain fallSoil moisture40- %30-39 %
Managements
20-29 %{Transplanting Date (Tp_date),
10-19 %Fertilizer Application Date (F_date),
0-9 % Fertilizer Application Rate (F_rate)}
Water surface
Dense plants
Urban area

Weather Data
{Solar Radiation (Sn), Average
Temperature (T), Precipitation(Pr), Day length(Dl)}

Crop simulation model
Photosynthesis

Water
Stress(Ws)Developmental Rate (Dvr)Harvest index(Hi)LAI (Lai)

Weather data
Soil moisture

Evaluation in
the present

Yield

Dry Matter (Dm)Fraction ofTranspirable
Soil Water(Ftsw)

Developmental Index (Dvi)
Respiration(Rm)Biomass

Leaf Area
Expansion
Water
Stress(Ws)Plant N Content (Pnc)

N uptake (Nu)

Soil Parameter{Soil OrganicCarbon(Soc)}

GCM output

N Pool (Npool)
N mineralization(Nm)

N loss(Nl)DateFigure 13. The concept of the model for simulating rice growth under rainfed
conditions (Homma et al., 2003a). Terms in ellipses are input variables. Fractionof transpirable soil water is derived from the sub-model for simulating water
budget shown in Figure 12.

Prediction for
the futureClimate (precipitation) change impacts on rice productionThe combined model was applied for theMusi river basin in Indonesia.
Rice production is divided into 4 ecotypes:
 Rainfed:
without irrigation facility(depending on rainfall)
106,000ha 1 or 2 crops/year
 Irrigated:with irrigation facility
110,000ha 2crops/year Tidal swamp:utilize tide for irrigation
240,000ha 1 or 2 crops/year Fresh water swamp:utilize recession water
350,000ha 1 crop/year

Musi river basin
Jakarta
Tidal Swamp
Rainfed paddies are
distributed widely in the area

IrrigatedFresh water swamp
5IrrigatedClimate (precipitation) change impacts on rice production

Relative yield

Simulation was conducted after calibration based on farmers’ fields investigation. Yield
was simulated for future climate (2050-2065) and compared against those for present
climate (1985-2012).
The yield was compared with relative yield (yield relative to that obtained in irrigatedecotype in dry season.

Present

Climate (precipitation) change impacts on rice production
1

Dry season rice

Rainy season rice

0.8

Impact assessment
0.60.4
gfdl_2_1
presentplanting

0.2
0600

0100200
DOY300500
Yield (g m-2)

The reduction could be
alleviated byadjustment of planting
month or developmentof drought tolerantvariety with fertilizer
enhancement.

Soil moisture (m3 m-3)

The large yield
reduction of rainfed rice
in rainy season under
GFDL 2.1 scenario was
due to lower soil
moisture content
during the beginning ofrainy season rice
planting.

Present●Future●Cont.
400●+Fertilizer〇+Drought tolerant〇+Drought tolerant + Fertilizer

400
300
200
100012345678
Planting month9101112

Salinity problem in relation to water
One of our activities evaluates rice productivity in saline affected area in northeast Thailand.
Salinity levels are classified into 5 classes in Thailand:
1: “very severely (salt crust >50%)”; 2: “severely (salt crust 10-50%)”……5: “no salinity”
Salinity area （class 2；
Our major investigated fields）

Salinity area（class 1）

Salt accumulation pond

Salinity problem in relation to water2016.11Non-vegetation
11.4%
area
Precipitation
624 mm(Aug.-Oct.)

2018.112019.11

14.6%

10.0%

269 mm

515 mmSalinity problem in relation to water

Salinity problem in relation to water
We are now accessing the salinity damage on rice production.
The salinity problem is mainly caused with rock salt under the ground in the area.
However, deforestation is thought to be involved in the background: deforestation increased theground water level in dry season which enhanced salt accumulation at the soil surface.

Rice yield

Rice yield(Central)

3F60

Forest area
(Northeast)

240t/ha（）Rice yield(Northeast)

101920（％20 ）
04060

80

2000

Forest area

Forecasts and countermeasures are necessary beyond decades
in relation to water.
80
4F