use of sea surface temperature for predicting optimum planting window for potato at pengalengan n.
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USE OF SEA SURFACE TEMPERATURE FOR PREDICTING OPTIMUM PLANTING WINDOW FOR POTATO AT PENGALENGAN. Rizaldi Boer Bogor Agricultural University E-mail: rizaldiboer@yahoo.com.

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use of sea surface temperature for predicting optimum planting window for potato at pengalengan

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

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

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
slide3
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

Planting

Onset of WS delay

slide4
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

> 3 month

Seed harvesting time

Planting time delayed

slide5
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

> 3 month

Seed harvesting time

Planting time delayed

methodology

3. Simulate yields using historical data for different planting time

4. Develop fitting curve for yield data against planting time

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

Methodology

1. Evaluate strength of ENSO signal

2. Crop model validation

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

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

spatial correlation between mjja rainfall and sst
Spatial correlation between MJJArainfall 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

form of relationship between ar j o and soi dmi m j
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

(a)

(b)

Line 1:1

Result of Validation

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

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

yearly yield pattern

Develop fitting curve using Fourier Regression

200 fitting lines

Determine planting date that give maximum yield

Yearly Yield Pattern
equation to predict opt from soi and dmi
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.
slide14

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

concluding remark
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

Planting

Onset of WS delay

concluding remark1
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

> 3 month

Seed harvesting time

Planting time

slide19

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)

slide20

10N

W

E

10S

70

50

110

90

IOD=SSTW-SSTE