Hasil Penelitian The Effect of Elevation on Planting Calendar in West Timor Using Agricultural Rainfall Index (ARI) Methods

Hasil Penelitian Jurnal Teknologi Pertanian Semi Arida, Vol.1 Nomor 1 (2013)

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The Effect of Elevation on Planting Calendar in West Timor Using Agricultural Rainfall Index (ARI) Methods

Jonathan E.Koehuan1 dan Juli Setyanto2

1 Dept. of Agricultural Engineering UKAW Kupang-NTT

Email : [email protected] 2 Lasiana Climatology Station – BMKG NTT

Abstract

Climate is one of the essential factors effecting agricultural production. Better understanding it potential and characteristic would pave the way to gain the optimal agricultural production. The variation of elevation effected rainfall that furthermore determined the dynamic of soil water availability and planting calendar. In dry land farming, the ultimate source of agriculture water is from the rainfall. It is understandable that to secure the farming process and/or to boost the production, the optimal use of climate resources is essential. The research with the aims to determine a planting calendar using Agricultural Rainfall Index (ARI) method and to determine the effect of elevation on planting calendar in West Timor has been conducted. The backbone of the study is by the analysis of climatology data that consists of rainfall, temperature and evapotranspiration data. The data based on the ten days series data of 20 consecutive years. The data was covered 16 climatology local stations that disperse in four districts namely Kupang, Timor Tengah Selatan (TTS), Timor Tengah Utara (TTU) and Belu. Total coverage rain fed areas is 14,635 Ha from total potential agricultural areas of 48,509 Ha. The planting calendar was determined using ARI Method while the identification of the relation regarding elevation and planting calendar was using statistical approached of regression and correlation. The results show that planting calendar has a variation from 130.25 – 190.25 days; furthermore there is a strong correlation between elevation and planting calendar that indicated in correlation coefficient of 0.81. Moreover, the research shows that with the increase of elevation there is an increase of planting calendar. The strong relation meet the polynomial function of Y = 13.54 – 0.04X + 9x10-6 X2 with the determination coefficient (R2) of 0.820.

Keywords: Planting Calendar, West Timor, Elevation, Agriculture Rainfall Index, Correlation, Polynomial

function

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Introduction

Climate is one of the essential factors

effecting agricultural production process. Better

understanding it potential and characteristic

would pave the way to gain the optimal

agricultural production. Rainfall and

evapotranspiration are the main climate’s

component that effecting plant development

and production. Estiningsih and Gatot (2003),

stated that climate especially rainfall is the

main constraint factor in the development of dry

land farming in NTT Province. The amount of

rainfall basically is sufficient for the dry land

farming in NTT, however due to the disperse

distribution and high intensity in the short

period prone to cause a cropping failure.

The hypothesis is that there are the

difference among the initial and the amount of

rainfall every year in the difference altitude in

West Timor – NTT. These phenomena

explained that elevation is one of the prime

climate controls in tropical areas, the highest

the altitude, the rainfall is higher to the certainty

limit and then would decrease (Tadjang, 1992).

The variation of rainfall furthermore affected the

infiltration that would determine the dynamic of

soil water availability. The variation of soil water

availability determine the variation of planting

calendar, especially in the rain fed farming in

semiarid areas ( Stasiun Klimatologi Lasiana,

2000). In rain fed farming or dry land farming,

the ultimate source of agriculture water is from

the rainfall. It is understandable that to secure

the farming process and/or to boost the

production, the optimal use of climate

resources is essential.

Understanding the importance and

problems, this researched aimed are to

determine the planting calendar in West Timor

based on elevation and to understand the

relation among planting calendar with elevation

in West Timor.

Basically, climate is the variation

pattern of temperature, humidity, atmospheric

pressure, wind, precipitation, atmospheric

particle count and other meteorological

variables in a given region over long periods.

The important climate component for the

agricultural process according to Soepriyo,

(1993) including rainfall, evapotranspiration,

temperature, soil temperature, sunshine

radiation, wind velocity, and air humidity.

Furthermore, climate components that are

affected in planting calendar include rainfall,

temperature, and evapotranspiration.

Supangat (1990), underline that rainfall

is a common form of precipitation in tropical

areas. Temperature is the degree of heat and

cold of various gasses in atmosphere. The

temperature various form place to place

depend on factors such as sun radiation, land

and sea dispersion, elevation, wind and

geographic location. Manan et al (1980) stated

that evaportranspiration is a combination of

evaporation and transpiration. So, the

evapotranspiration is the amount of water that

evaporates from soils, water bodies, and living

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organisms. Furthermore, the potential

evapotranspiration is determined by

temperature, wind, humidity, and sunshine

radiation.

Elevation is a one of the climate

controlling factors in tropical areas, mainly to

rainfall and temperature ( Tadjang, 1992). The

highest the elevations tend to increase rainfall

to the certain limit the rainfall would decrease.

Sosodarsono and Tekeda (1997) stated that

rainfall in mountain areas more than in plain

areas with the linear relationship. Manan et all

(1980) underline that the highest the elevation

the lower the temperature.

Planting calendar is a timescale in

which soil moisture support the development of

corps. Soil water balance in the dry land mostly

depends on rainfall as an input and

evapotranspiration as an output from soil and

crops. In order to reduce the water stress

during the growing period, it is important to

determine the timescale in which the rainfall

filling up soil moisture that can be sufficient for

the crops growth and harvesting.

Agricultural rainfall index is a

parameter to determine the availability of soil

moisture for the crops growth (FAO, 1984).

During the dry season, mostly in West Timor

the soil moisture become dramatically

decrease due to lack of rainfall, on the other

hand the evapotranspiration become high that

can accelerate the permanent wilting point.

Growing season in dry land can be

implemented after the soil obtains the supply

form the optimal rainfall so it can be in field

capacity. The rainfall that can supply the water

availability is known as effective rainfall. The

effective rainfall furthermore is statistically a

80% of the rainfall. Soil water availability in the

dry land can be estimated using Agricultural

Rainfall Index (ARI) method. Planting calendar

can be determined based on the index between

0 – 1, where the suitable soil water condition

for crop growth is above 1. In Indonesia the

seasonal period is from September to August in

a year period.

Methods

The population is West Timor dry land

areas from the elevation of 5 MSL to 1,129

MSL in which it sampling by the purposive

sampling technique. There are 16 climatology

observation posts that disperse in four districts

namely Kupang, Timor Tengah Selatan, Timor

Tengah Utara and Belu with four degree of

elevation. The elevation and observation posts

are:

1. 0 – 300 MSL consists of four posts that

are Naikliu (5 MSL) ; Lasiana (20

MSL); Panite (44 MSL) and Betun (53

MSL).

2. 301 – 600 MSL consists of four posts

of Nenuk ( 365 MSL); Kefamenanu (

381 MSL); Oekabiti (415 MSL) and

Oe’ekam (537 MSL).

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3. 601 – 900 MSL consists of four posts

of So’e (742 MSL); Niki-niki (793 MSL);

Lelogama (872 MSL) and Kesetnana

(882 MSL).

4. 901 – 1,200 MSL consists of Nulle

(919 MSL); Oelbubuk ( 1007 MSL);

Netpala (1010 MSL) and Eban (1129

MSL).

Agricultural Rainfall Index (ARI) is

calculating using the formula of:

ARI = P / ETo ........................... (1)

Where:

ARI = Agricultural Rainfall Index P = Rainfall (mm) ETo = Potential Evapotranspiration (mm)

Furthermore the potential

evapotranspiration is calculating using the

formula:

ETo = Eo x Kp …………………………… (2)

Where:

ETo = Potential evapotranspiration (mm) Eo = Potential evaporation (mm) Kp = Pan evaporation coefficient

The determination of soil water

availability is using Agricultural rainfall index

(ARI) criteria. The planting calendar is

estimated based on the month that has an ARI

value more than 1 (>1).

Table1. Soil Water Availability Criteria Based on Agricultural Rainfall Index

No. ARI Value Soil Criteria

1. < 0.6 Dry Soil 2. 0.6 - 1 Moist soil 3. > 1 Wet soil

The correlation of elevation and planting

calendar is calculating using the correlation

coefficient formula (Rianse and Abdi, 2009).

……………………………………………(3)

Where:

xy = Correlation coefficient of elevation (X)

and Planting Calendar (Y) N = Sum of the data

X = Sum of X value

Y = Sum of Y value 2X = Sum square of X value

2Y = Sum square of Y value

2X = Sum of X value squared

2Y = Sum of Y value squared

XY = Sum of X and Y multiplication

In order to understand the effect of

elevation on planting calendar is estimated

using the second order of polynomial

regression with the common formula of:

Y = a0 + a1 X + a2 X2………………… (4)

Where:

Y = Planting calendar (ten days) X = Elevation (m) a0, a1, and a2 = Regression coefficient

2222 YYNXXN

YXXYNrxy

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Result and Discussion

Geographically West Timor is located

in 1230 27’ 40” – 1250 11’ 59” East Longitude

and 080 56’ 17” – 100 21’ 56” South Latitude.

According to BPS NTT (2009), West Timor has

a potential dry land area of 30% or 14,635 Ha

from total potential agricultural land of 48,509

Ha. The topography in the area is variety from

plain, hilly and mountainous areas. The plain

area is utilized as farm land in Kupang, TTU

and Belu districts. Hilly and mountainous areas

are utilized as plantation that mainly in TTS

district.

As a semi arid region, West Timor has

two seasons yearly that are rain and dry

seasons. Rain season occur in November to

February due to the Asian monsoon that carry

steam from Asia. On the other hand, dry

season occur during Mei to August due to the

dry monsoon from Australia. There are also

transition periods on September to October and

March to April.

Rainfall

Average ten days rainfall in 20 years of

elevation 0-300 MSL between 33 mm to 45

mm, with minimal 0 mm and maximum of 168

mm. The average rainfall in Naikliu (5 MSL) is

36 mm with the maximum of 124 mm. The

average rainfall in Lasiana (20 MSL) is 45 mm

with the maximum of 168 mm. The average

rainfall in Panite (44 MSL) is 33 mm with the

maximum of 80 mm, and the average in Betun

(53 MSL) is 38 mm with the maximum of 131

mm.

Figure 1. The Average Rainfall of Four Stations in Elevation of 0-300

The average rainfall of elevation 301 –

600 MSL is 34 mm to 52 mm. The minimal

rainfall for all stations is 0 mm. The average

rainfall in Nenuk (365 MSL) is 52 mm with the

maximum of 178 mm; in Kefamenanu (381

MSL) is 34 mm with the maximum of 104 mm;

in Oekabiti (415 MSL) is 45 mm with the

maximum of 172 mm; and the average rainfall

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in Oe’ekam (537 MSL) is 37 mm with the maximum of 105 mm.

Figure2. The Average Rainfall of Four Stations in Elevation of 301-600 MSL

The minimum rainfall of four stations in elevation of 601 to 900 MSL is 0 mm except So’e (742 MSL) and Lelogama (872 MSL) are 1 mm. The average rainfall in So’e (742 MSL) is 48 mm, Niki-Niki (793 MSL) is 37 mm,

Lelogama (872 MSL) is 70 mm and Kesetnana (882 MSL) is 44 mm. The maximum rainfall in So’e is 149 mm; Niki-Niki is 102 mm; Lelogama is 238 mm and Kesetnana is 122 mm.

Figure3. The Average Rainfall of Four Stations in Elevation of 601-900 MSL

The minimum rainfall of four station in elevation 901 to 1,200 MSL is 0 mm except in Netpala (1,010 MSL) of 4 mm. The average rainfall in Nulle (919 MSL) is 42 mm; in Oelbubuk (1,007 MSL) is 57 mm, in Netpala

(1,010 MSL) is 58 mm and in Eban (1,129 MSL) is 58 mm. The maximum rainfall in Nulle is 120 mm, in Oelbubuk is 169 mm, in Netpala is 175 mm and in Eban is 151 mm.

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Figure4. The Average Rainfall of Four Stations in Elevation of 900-1,200 MSL

Evapotranspiration

The average of ten days

evapotranspiration of 20 consecutive years in

0-300 MSL is 46 mm to 48 mm. The average

evapotranspiration in Naikliu (5 MSL), Lasiana

(20 MSL) and Panite (44 MSL) is 48 mm, while

in Betun ( 53 MSL) is 46 mm. The maximum

evapotranspiration is between 61 – 63 mm

while the minimum are 30 mm – 34 mm.

Figure5. The Average Evapotranspiration of Four Stations in Elevation of 0-300 MSL

The minimum evapotranspiration in

elevation 301 – 600 MSL varied between 36 –

38 mm while the maximum varied between 59

mm – 63 mm with the average varied between

43 mm – 46 mm. The average

evapotranspiration in Nenuk (365 MSL) is 50

mm, in Kefamenanu (381 MSL) is 49 mm, in

Oekabiti (415 MSL) is 47 mm, and in Oe’ekam

(537 MSL) is 48 mm.

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Figure6. The Average Evapotranspiration of Four Stations in Elevation of 301-600 MSL

The minimal evapotranspiration in

elevation 601 to 900 MSL varied from 34 mm to

35 mm. The maximal evapotranspiration varied

from 55 mm to 57 mm with the average of 43

mm to 46 mm. The average evapotranspiration

in So’e (742 MSL) is 46 mm, in Niki-niki (793

MSL) is 45 mm, in Lelogama (872 MSL) and

Kesetnana (882 MSL) is 43 mm.

Figure7. The Average Evapotranspiration of Four Stations in Elevation of 601-900 MSL

The minimal evapotranspiration in

elevation 901 to 1,200 MSL varied from 32 mm

to 34 mm. The maximal evapotranspiration

varied from 52 mm to 56 mm with the average

of 41 mm to 42 mm. The average

evapotranspiration in Nule (919 MSL) and

Oelbubuk (1,007 MSL) is 42 mm while in

Netpala (1,010 MSL) and Eban (1,129 MSL) is

41mm.

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Figure8. The Average Evapotranspiration of Four Stations in Elevation of 901-1,200 MSL

Planting Calendar

Planting calendar depict the begining

and last of planting season. In West Timor the

average planting calendar begins in Nopember

I and last in Mei III. The shortest period of

planting calendar is 120 days ( 12 ten days)

and the longgest is 200 days ( 20 ten days).

The shortest period happen in lower elevation (

0-300 MSL) and the longgest happen in higher

elevation of 901 – 2,001 MSL.

Planting calendar in elevation 0-300

MSL begins in November III and last in April II.

Planting calendar in elevation 301 – 600 MSL

from November II to April I. Planting calendar

in elevaion 601-900 MSL begins in November I

and last in April II. While the planting calendar

in elevation 901 – 1,200 MSL is from

November I to Mei III.

The Correlation and Regression of Elevation and Planting Calendar

Correlation and regression were use to

examine the relationship of elevation and

planting calendar. There is a strong correlation

between elevation and planting calendar in

West Timor. The strong correlation is indicate

by the value of correlation coefficient of 0.81

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Table2. Planting Calendar in Various Elevation of West Timor

No. Elevation

Grade (MSL)

Location Elevation

(MSL) Begin Last

Period (Ten

Days) Days

1

0-300

Naikliu 5 November III Maret III 13 130 2 Lasiana 20 November III Maret II 12 120 3 Panite 44 November III April I 14 140 4 Betun 53 Desember I April II 14 140 5

301 - 600

Nenuk 365 November II April I 15 150 6 Kefamenanu 381 November II Maret III 14 140 7 Oekabiti 415 November III Maret III 13 130 8 Oe'Ekam 537 Desember I April I 13 130 9

601 - 900

So'e 742 November II April I 15 150 10 Niki-niki 793 Desember I April II 14 140 11 Lelogama 872 November I April II 17 170 12 Kesetnana 882 November II April I 15 150 13

901- 1,200

Nulle 919 November I April III 18 180 14 Oelbubuk 1,007 November II Mei III 20 200 15 Netpala 1,010 November I Mei I 19 190 16 Eban 1,129 November II Mei III 20 200

The strong relation of elevation and planting calendar meet the second order of polynomial regression, the formula is Y = 13.54 – 0.004X + 9x10-6 X2 with the determination coefficient of 0.82. Correlation and regretion analysis show that the increasing of elevation the longest the planting calendar.

In West Timor with the higher the elevation that would be the more intense and

longer rainfall period, on the other hand the higer the elevation, the evaporation tend to decrease. The proportion of rainfall and evapotranspiration in higher elevation more higher than in the lower elavation, the consequence is the higer elevation has the longest planting calendar.

Figure9. The Polynomial Relation of Elevation and Planting Calendar

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Conclusion

The average planting calendar period

at an elevation of 0-300 MSL comparatively

shorter (133 days) when compared with the

elevation of 301-600 MSL (138 days), elevation

601-900 MSL (153 days) , while the average

planting calendar longest period at an elevation

of 901 - 1200 MSL (193 days).

There is a very close relationship

between elevation and planting calendar in

West Timor that indicated by correlation

coefficient of 0.81.The increasing elevation

from sea level, likely the longer the period of

planting calendars in West Timor, which can be

explained by second order polynomial

regression equation as follows: Y = 13.54 to

0.004 X + 9x10-6X2 with a coefficient of

determination R2 = 0.820.

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