Friday, May 15, 2009

Soil distribution in the Philippines

The distribution of soils in the Philippines is largely controlled by parent material, relief, and vegetation. In general, Philippine soils are younger than the tropical soils in mainland Asia, Central and South America, and Africa. This is because most Philippine islands are geologically young since they were the result of, just like much of Southeast Asia, recent Cenozoic tectonic events and have emerged from the sea recently (Hall, 2002).

Philippine soils maybe grouped based on geomorphology and for practical purposes, into: soils in lowland areas, soils in young and unstable uplands, and soils in old and stable uplands.

Soils in lowland areas

Lowland areas include all flatlands located near sea level. Most of these areas are underlain by recent alluvial sediments. Because of this and due to periodic deposition of sediments during flooding events, the soils in lowland areas are poorly developed.

Arenosols (Entisols)
. These are weakly developed sandy soils common in alluvial plains andcoastal areas.
Gleysols (Entisols, Inceptisols)
. These are the poorly developed wet soils in alluvial plains and marshes. They are used chiefly for lowland rice production. Together with Histosols, Gleysols are the dominant soils of wetlands.
Cambisols (Inceptisols)
. These are weakly developed soils showing poor horizon B development. They occur in association with Gleysols although they can also be found in mountainous areas.
Fluvisols (Entisols)
. These are the undeveloped soils commonly found along rivers. Periodic deposition of river sediments retard soil development.
Vertisols (Vertisols)
. These are the clayey soils in lowland areas that produce large cracks on the surface during the dry season. They are very fertile and are widely used for lowland rice production. A typical example can be found in Mangaldan, Pangasinan.
Histosols.
These are found in swamps, marshes, shallow lakes, and depressions. The saturated condition favors the accumulation of organic materials. Large areas are found in Leyte, Samar and Surigao.

Soils in young and unstable uplands

Uplands are undulating as well as hilly lands ranging in elevation from near sea level to about 1000 meters. Many upland areas around the country are the result of recent volcanic activity or geologic uplift. These are young landscapes underlain by young volcanic deposits or reef limestone and thus have also poorly developed soils.

Leptosols (Entisols, Inceptisols). These are the shallow soils (less than 50 cm deep) in rocky areas. Many soils derived from limestone in various islands have very thin solum and thus they belong to Leptosols.
Andosols (Andisols).
These are the poorly developed soils on young volcanic landscapes in the mountains of Negros, Leyte, Bicol, Taal and other volcanic areas of the country. The soil is soft and very friable and appears dark due to the high organic matter content. Except for their very low P availability, the properties of these soils are generally favorable for crop production.
Chernozems (Mollisols)
. These are very fertile soils due to their organic matter-rich topsoil. They can be found in limestone areas in Leyte, Bohol and other islands.

Soils in old and stable uplands

Old uplands were formed by volcanism or geologic uplift millions of years ago. They typically occur on the lower slopes of volcanic mountains. Soils in these areas are well-developed or highly weathered.

Ferralsols (Oxisols). These are the very deep, red, acidic and very infertile soils found in old landscapes in Palawan, Mindanao, and Samar.
Acrisols and Alisols (Ultisols)
. These are the reddish, clayey, acidic soils widespread in hilly and mountainous areas throughout the archipelago.
Luvisols (Alfisols)
. These are the well-developed soils with high base saturation (fertile) found in old alluvial terraces in various areas in the Philippines.

(Photo above shows the typical soil-landscape relationship in the volcanic island of Leyte)

References

Asio VB. 1996. Characteristics, weathering, formation and degradation of soils from volcanic rocks in Leyte, Philippines. Hohenheimer Bodenkundliche Hefte vol. 33, Stuttgart.

Asio VB, PP Garcia, GAA Garcia. 2005. Development of a new soil map of Leyte. Unpublished project report, VSU, Baybay, Leyte.

Barrera A, F Aristorenas, JA Tingzon. 1954. Soil survey of Leyte province, Philippines. Soil Survey Report No. 18, Bureau of Print, Manila.

Bureau of Soil and Water Management (undated). Soil map of the Philippines (1:7,500,000). http://www.fap.org/ag/AGL/swlwpnr/reports/y_ta/z_ph/phmp231.htm#s133.

Hall R. 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: model and animation. J. Asian Earth Sci. 20: 353-431.

Hirayama R, R Carating, T Ohkura, V Castaneda, M Vinluan. 2002. The soils of the Philippines. Proc. 3rd and 4th symposia on collection building and natural history studies in Asia and the Pacific Rim (T Kubodera et al., eds). National Science Museum Monographs 22: 109-113.


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