FARMING SYSTEMS DICTATED BY AGROECOLOGICAL
CONDITIONS IN SOUTHEAST ASIA
M. Zaki Ghazali
ABSTRACT
The agroecology of Southeast Asia has been classified on a large scale by making use of rainfal1 data
In this paper, an agro-climatic classification based on rainfall data is presented. Rainfall and dry
period distributions are used to assess the suitability of food crops in the agro-climatic zones. While
data on the forages are scarce, the methodology can be applied to these crops.
INTRODUCTION
The climatic environment of the humid tropics of Southeast Asia is conditioned by its geographic
position on one hand and by the local topographic differences on the other. While the climate varies
from extremely dry zones with annual rainfall below 500 mm to extremely wet zones with over 7000
mm annually, there are certain climatic patterns in the region that prevail over major parts of the area.
The climatic changes from month to month are related largely to the general air circulation over
this part of the world. Within latitudes of 30 deg N and S of the Equator, the surface of the earth
absorbs more heat by solar radiation than it loses by terrestrial radiation. Outside these latitudes the
situation is reversed. The atmosphere regulates these differences. Because of the heating of the earth
there exists a temperature decrease in the troposphere from the Equator to the higher latitudes. There
is also a vertical drop in temperature until the tropopause.
Unequal heating creates air streams in the atmosphere which have a zonal direction because of
the earth's rotation. These airstreams, however, neither have constant direction nor constant speed.
Near the earth surface their direction is influenced by temperature differences between the continents,
the ocean streams and the mountain chains. A typical atmospheric circulation over Southeast Asia in
July is described by Oldeman (1982).
AGRO-CLIMATIC CLASSIFICATION
In general a fair amount of data on rainfall is available for most parts of the Southeast Asian countries.
However, other macro-climatic parameters such as evaporation, temperature, relative humidity, wind
speed, and particularly solarradiation are seldom recorded. Thus it has been difficult to evaluate the
regional evapotranspiration scenario. Thus rainfall has been used as the dominant factor in most
agro-climatic studies (IRRI 1974, Oldeman (undated), Nieuwolt et. al. 1982).
In evaluating rice cropping systems potentials in Southeast Asia (IRRI 1974), the main criterion used
for selecting major climatic zones was monthly rainfall. An arbitrary boundary was set at 200 mm.
This amount is based on two assumptions: (1) Losses due to evaporation, although variable over the
year, generally amount to around 100 mm per month; and (2) Losses due to percolation and seepage,
although variable, depending on soil characteristics, are generally set ar~ around 100 mm per month.
The following zones were delineated.
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1)
Zone I. Areas with more than nine consecutive wet months (rainfall greater than 200 mm per
month). This zone includes the major pert of Kalimantan and East Malaysh, central Sumatra and
along the northwest coast of Sumatra and eastern parts of Philippines (Fig. 1a & b).
2)
Zone II. Areas with five to nine consecutive wet months. This climatic characteristic covers most
of Malaysia, Indonesia and the Philippines. The rainfall peaks are separated by months of
rainfall between 100 to 200 mm per month or less than 100 mm which then would be a dry
month
Since this zone is of interest for multiple cropping, it is divided into four sub-divisions.
a) Zone II.1. Areas with five to nine consecutive wa months and with 100 to 200 mm rainfall
per month during the remaining part of the year. Year-round cropping is possible with one
crop of puddled rice.
b) Zone II.2. Areas with five to nine consecutive wet months and with 100 to 200 mm rainfall
per month during the remaining part of the year and with another minor rainfall peak. This
area is equally suitable for multiple cropping although farmers are likely to grow two crops
of puddled rice.
c) Zone II.3. Areas with five to nine consecutive wet months and with at least two months of
less than 100 mm per month rainfall. This area covers large part of central and east Java,
southern Thailand, eastern and southeast Thailand, southern Burma, and major parts of the
Philippines.
d) Zone II.4. Areas in the southeast and east of Thailand are characterised by a sharp end to the
rainy season; the dry season in these areas and in parts of Burma is very pronounced with
virtually no rain during 2 to 3 months.
3)
Zone III. Areas with two to five consecutive wet months. Although the wet season may often be
too short to grow two crops of rice, areas that receive 100 mm or more of rainfall per month
during the dry season have been separated from those that receive less than 100 mm per month
during the dry season:
a) Zone III.I. Areas with two to five consecutive wet months but with at least 100 mm rainfall
per month during the remainder of the year.
b) Zone III.2. Areas with two to five consecutive wet months and a pronounced dry season with
at least 2 months less than 100 mm rainfall per month.
1)
Zone IV. Areas with less than two consecutive wet months. These areas are not suitable forany
type of agriculture unless additional water is available.
AGRO-CLIMATIC SUITABILITY ASSESSMENT
There is a dearth of information on the environmental requirements of forages and grasses. The
fact that there is a phylogenetic similarity among the forages and grasses associated with natural
grasslands throughout the tropical regions of the world (Most and Popenoe, 1977), shows that these
plants are highly adaptable to the environment. Further studies need to be carried out to screen the
valuable livestock food sources that are best suited for each environment. (TABLE 1)
To date most crop adaptability studies are done on the human food crops. Since most of these
crops provide residues that are important as animal feeds, in the following paragraphs the regional
distribution of these crops are discussed. Any grass and forage crops that have similar environmental
requirements as the human food crops, will also possibly thrive well in the same environment.
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Table 1. Attributes of climatic and edaphic adaptability of some crops
ATTRIBUTE
Millet
Sorghum
Maize
Soybean
Grdnut
Sorghum
Highland
Maize
Cassava
>70
>70
40-50
>70
40-50
optimum temperature (C)
30-35
30-35
25-30
20-30
25-30
operative range (C)
15-45
15-45
15-35
10-35
15-35
Radiation intensity at
max PS (cal/cm2/min)
1.0
1.0
0.3-0.8
1.0
0.3-0.8
Length of growth cycle
70-120
90-120
90-120
>120
180-330
Seed
Seed
Seed
Seed
Tuber
Warm
W
W
M Cool
W
0-8
0-8
0-8
0-8
0-8
MW-W
MW-W
MW-W
MW-W
W
Climatic adaptability
Photosynthesis rate at
light saturation
(mgCO2/dm 2/h)
Harvested part
Suitable thermal climate
for rainfed production
Edaphic Adaptability
Slope %
(optimum)
Drainage
Flooding
Texture
Optimum
------------------- no flooding ------------------
Margina1
-------------------- occasional flooding -----------------
Optimum
L-CL
Marginal
Depth (cm)
L
L
L
L
--------- kaolinitic clay ---------------- >50 ---------
>100
pH
5.5-8.2
5.5-8.2
5.5-7.5
5.5-8.2
5.2-7.0
Fertility
low/med
med
med
low/med
low
0-5
0-4
0-3
0-4
0-2
Salinity (mmhos)
(After Kassam, et.al, 1980)
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The grains - millet, sorghum, maize.
Millet and sorghum are drought-resistant crops. They are extensively grown under rain-fed
conditions in the dry areas. They do not tolerate prolonged water-logging. Their water requirement
is minimal - 450 to 650mm during the growing period. They are thus found to be suitable in the drier
parts of the region (Zones III and IV).
Maize requires more water - 500 to 800 mm depending on the climate. The crop is found more
extensively in the region but still requires distinct dry periods during the ripening stage. The crop
extends into Zone II, depending on the climate, soil and terrain.
The grain legumes - soybean.
The small legumes require relatively little water, 300 -500 mm during the growing period The
greatest demand is during the vegetative mid-season stage. At maturity and ripening, the evapotranspiration is minimum, thus a dry condition is preferable. These crops thrive well in the II.2 and drier
zones. The tree legumes would presumably tolerate mare humid conditions, thus should be able to be
widely grown in the southeast asian region, depending on the soil conditions. Most tropical soils are
acidic in nature with high exchangeable aluminium that need to be adjusted.
Cassava
Cassava is a crop adaptable to the warm, humid tropical climate and therefore is commonly
grown in Southeast Asia. It is found to be suitable for most countries in the region.
REFERENCES
IRRI (1974). An agro-climatic classification for evaluating cropping systems potentials in Southeast Asian
regions.
Kassarn A H., H.T Van Velthuizen, G.M. Higgins, A. Chrisbafrides, R.L. Voortman and B. Spiers (1980).
Assessment of land resources for rainfed crop production in Moz unbique. FAO/AGOA: MOV75/011.
Oldanan, L.R., (undated). The agro-climatic classification of rice growing environments in Indonesia. Central
Research Institute for Agriculture, Indonesia~.
(1982). A Study of the Agroclimatology of th Hu nid Tropics of South-East Asia, FAO-WMO.
Mott, C.O. and H.L. Popenoe. Grasdands. In P.T. Alvim and T.T. Kozlowski (eds.). Ecophysiology of Tropical
Crops. Academic Press N.Y. 1977. p 157 -186.
Nieuwolt, S., M2. Ghazalli and B. Gopinathan (1982). Agro-ecological Regions in Peninsular Malaysia. MARDI.
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