USE OF SEA SURFACE TEMPERATURE FOR PREDICTING

OPTIMUM PLANTING WINDOW FOR POTATO AT PENGALENGAN

Rizaldi Boer

Bogor Agricultural University

E-mail: rizaldiboer@yahoo.com

Introduction• Pengalengan is the main potato

production centre – 76% of potato production of

Bandung district comes from Pengalengan, while Bandung district contributes 60 % to total production of West Java

– Significant reduction in production Pengalengan will have great influence of potato supply in the region

W e s t J a v a

P e n g a l e n g a n

B a n d u n g D i s t r i c t

0

150

300

450

600

750

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

Month

Pla

ntin

g A

rea

(ha)

Porekat Ceboran Wuku

• There planting season for potato called Porekat (January-April), Ceboran (May-July) and Wuku (September-December). Yield at Ceboran are mostly for seeds not for trading

• ENSO may affect potato farmers in a number of ways:– False rains that may occur early

September normally triggered farmers to start planting, while the actual onset of WS may delayed to October or November. Crop will have low yield due to poor seedling

– Farmers who delay their planting up to November due late onset of rainy season may also have low yields as the seeds produce in Porekat season will lose their viability as they were kept more than 3 months

• Thus, method for predicting optimum planting window based on sea surface temperature (ENSO indicator) prior to the planting season is required to overcome the above two problems

0

150

300

450

600

750

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

Month

Pla

nti

ng

Are

a (h

a)

Porekat Ceboran Wuku

Plantin

g

Onset of W

S

delay

• ENSO may affect potato farmers in a number of ways:– False rains that may occur early

September normally triggered farmers to start planting, while the actual onset of WS may delayed to October or November. Crop will have low yield due to poor seedling

– Farmers who delay their planting up to November due late onset of rainy season may also have low yields as the seeds produce in Porekat season will lose their viability as they were kept more than 3 months

• Thus, method for predicting optimum planting window based on sea surface temperature (ENSO indicator) prior to the planting season is required to overcome the above two problems

0

150

300

450

600

750

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

Month

Pla

nti

ng

Are

a (h

a)

Porekat Ceboran Wuku

Planting tim

e delayed

Seed harvesting

time

> 3

month

• ENSO may affect potato farmers in a number of ways:– False rains that may occur early

September normally triggered farmers to start planting, while the actual onset of WS may delayed to October or November. Crop will have low yield due to poor seedling

– Farmers who delay their planting up to November due late onset of rainy season may also have low yields as the seeds produce in Porekat season will lose their viability as they were kept more than 3 months

• Thus, method for predicting optimum planting window based on sea surface temperature (ENSO indicator) prior to the planting season is required to overcome the above two problems

0

150

300

450

600

750

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

Month

Pla

nti

ng

Are

a (h

a)

Porekat Ceboran Wuku

Planting tim

e delayed

Seed harvesting

time

> 3

month

Methodology1. Evaluate strength of ENSO signal1. Evaluate strength of ENSO signal

2. Crop model validation2. Crop model validation

3. Simulate yields using historical data for different planting time 3. Simulate yields using historical data for different planting time

4. Develop fitting curve for yield data against planting time4. Develop fitting curve for yield data against planting time

5. Determine planting time that give maximum yield for the curves (OPT)5. Determine planting time that give maximum yield for the curves (OPT)

6. Develop distribution of OPT to define optimum planting window (OPW)6. Develop distribution of OPT to define optimum planting window (OPW)

7. Develop equation to predict OPT from sea surface prior to the OPW7. Develop equation to predict OPT from sea surface prior to the OPW

Spatial correlation between MJJA rainfall and SST

Relationship of seasonal rainfall with SST at Pacific is consistently negative while with Indian Ocean is consistently positive,

particularly for dry season rainfall

Relationship between ARJ-O and SOI/DMIM-J

Margahayu

y = 13.45x + 11.147

R2 = 0.203

-600

-400

-200

0

200

400

600

800

-30 -20 -10 0 10 20

SOI (Mei-Juni)

Ra

infa

ll A

no

ma

ly (

Jul-

Oct

)

Margahayu

y = -205.25x + 13.862

R2 = 0.065

-600

-400

-200

0

200

400

600

800

-1 -0.5 0 0.5 1

IOD (Mei-Juni)

Ra

infa

ll A

no

ma

ly (

Jul-

Oct

)

Montaya

y = 18.958x - 1.615

R2 = 0.3496

-600

-400

-200

0

200

400

600

800

-30 -20 -10 0 10 20

SOI (Mei-Juni)

Ra

infa

ll A

no

ma

ly (

Jul-

Oct

)

Montaya

y = -191.7x + 19.241

R2 = 0.0337

-600

-400

-200

0

200

400

600

800

-0.5 0 0.5 1

IOD (Mei-Juni)

Ra

infa

ll A

no

ma

ly (

Jul-

Oct

)

DMI

DMI

Form of Relationship between ARJ-O and SOI/DMIM-J

• ARJ-O=a + bSOIM-J + c(SOI*DMI)M-J

– The R2 ranged between 22% and 56% with mean of 37% – Values of coefficients b and c are 0

• This means that if the SOI is negative (indicating El-Nino) and DMI is also negative (sea surface temperature in the region of 90°E - 110°E/ 10°S –equator, near Indonesia is higher than that of 50°E - 70°E/10°S - 10°N or IDM occurs), the (SOI*DMI) value will be positive. This means that the DMI negative will counteract the reducing effect of El-Nino on rainfall. This finding is in agreement with previous studies (Yamagata et al. 2001; Kumar et al. 1999)

Result of Validation

0

5

10

15

20

25

30

35

6/1/

2002

6/4/

2002

6/5/

2002

6/11

/200

26/

12/2

002

6/12

/200

26/

15/2

002

6/15

/200

26/

15/2

002

9/1/

2002

9/2/

2002

9/3/

2002

9/5/

2002

9/5/

2002

9/9/

2002

9/15

/200

29/

15/2

002

9/16

/200

29/

17/2

002

9/18

/200

29/

19/2

002

10/7

/200

211

/1/2

002

1/3/

2003

1/5/

2003

1/10

/200

32/

15/2

003

2/20

/200

3

Planting Time

Yie

ld (t

/ha)

ObservedSimulated

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Simulated Yield (t/a)O

bser

ved

Yie

ld (t

/ha)

Line 1:1

(a) (b)

Model is able to mimic real system. This means that it can be used to study how past climate affect yield variability

Observed yield data for the validation were collected from 28 farmers planted their crop in the period of June 2002-February 2003

Yearly Yield Pattern

Ceboran without Irrigation

0

5

10

15

20

25

30

35

40

1-J

an

15

-Jan

1-P

eb

15

-Peb

1-M

ar

15

-Mar

1-A

pr

15

-Ap

r

1-M

ei

15

-Mei

1-J

un

15

-Ju

n

1-J

ul

15

-Ju

l

1-A

gt

15

-Ag

t

1-S

ep

15

-Sep

1-O

kt

15

-Ok

t

1-N

ov

15

-No

v

1-D

es

15

-Des

Planting Time

Yie

ld (

t/ha)

Determine planting date that give maximum yieldDetermine planting date that give maximum yield

Develop fitting curve using Fourier RegressionDevelop fitting curve using Fourier Regression

n

kkkt ktcktbaY

10 )]'cos(*)'sin(*[

200 fitting lines

Distribution of OPT and yield at optimum planting time for Wuku Season

Ceboran without Irrigation

0

10

20

30

40

50

60

2/29

3/15

3/30

4/14

4/29

5/14

5/29

6/13

6/28

7/13

7/28

8/12

8/27

9/11

9/26

10/1

110

/26

11/1

011

/25

12/1

012

/25

Planting Date

Fre

quen

cy

OptimumPW

Ceboran without Irrigation

0

15

30

45

60

75

10 15 20 25 30 35 40 45 50

Yield (t/ha)

Fre

quen

cy

EQUATION TO PREDICT OPT FROM SOI AND DMI

• As SOI and DMI has significant impact on rainfall variability, and rainfall variability has significant impact on yield variability, the SOI and DMI can be used to define optimum planting time (OPT)

• The form of the relationship is the same as that of rainfall– OPTW = 272 + 0.843 SOIJA - 1.57 (SOI*DMI)JA

• The equation suggests that when El-Nino occur (SOI negative) but DMI also strongly negative (Indian Dipole Mode also occur), the onset of rainy season may not delay and therefore planting early in the Wuku season should have no risk. But if DMI strongly positive, then planting early in the Wuku season (early September) is not suggested.

0

SOI

-30 –25 –20 –15 –10 –5 0 +5 +10 +15 +20 +25 +30

+1.5

+1.0

-1.0

-1.5

DM

I Julian Days

This approach can also be used to estimate expected yield of potato planted in Wuku season from July-August SOI and DMI

Estimated Potato Yield at different planting time and different SOI/DMI

Concluding Remark

• Having capability to predict optimum planting time will help potato farmers in:– Avoiding drought risk at

initial stage of crop development if onset of WS is expected to delay based on SOI/DMI May-June Information

0

150

300

450

600

750

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

Month

Pla

nti

ng

Are

a (h

a)

Porekat Ceboran Wuku

Plantin

g

Onset of W

S

delay

Concluding Remark

• Having capability to predict optimum planting time will help potato farmers in:– Deciding which seeds

produced at Ceboran season should be sold and kept for planting in Wuku Season

0

150

300

450

600

750

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

Month

Pla

nti

ng

Are

a (h

a)

Porekat Ceboran Wuku

Planting

time

Seed harvesting

time

> 3

month

The Indian Ocean, like the Pacific, has an El Niño. A warm pool in the Indian Ocean moves eastward (1 to 3) in a cycle of 3 to 7 years. The same phenomenon

occurs in the Pacific (4 to 6)

10N

10S

7050 11090

EWIOD=SSTW-SSTEIOD=SSTW-SSTE