The Philippine islands are part of a circum-Pacific volcanic belt. There are many volcanoes and volcanic ash soils including 'Kuroboku-do', 'Andosols', 'Andepts' and 'Andisols', are widely distributed in this country.
The objective of this study is to investigate the distribution of volcanic ash soils including their morphological characteristics, physico-chemical properties and characteristics of organic matter in relation to clay mineralogy for the purpose of comparing these parameters with those of corresponding soils in Japan.
Tagaytay soils are found on the northwestern slope of Taal volcano. Organic matter content decreases with decreasing elevation. They also show a high base saturation. The young volcanic ash and pumice have high total phosphorus contents. The buried humic layers and the A horizon were developed 1170 ± 70 yrs.B.P. and 710 ± 100 yrs.B.P.,respectively.
Caliraya soil derived from Mt. Banahaw ejecta has a very low pH, high exchangeable aluminum content, low base saturation, low phosphate absorption and high peak of halloysite in the X-ray diffraction pattern. The soil may represent a transition from Andisols to Ultisols.
Isarog soil showed the highest soil organic matter contents, high pH (NaF), high phosphate absorption and water contents but low exchangeable cation contents and bulk density. A similar behavior was observed for the Kuroboku soils with amorphous X-ray patterns in Japan. The age of the humic layers ranged from 580 ± 90 yrs.B.P. to 610 ± 90 yrs.B.P.
lriga soil in the Bicol area has a high pH, high exchangeable cation contents and base saturation.
There were two types of soils from Mayon volcanic ash: one consisting of relatively old ash with a fine texture, high phosphate absorption and water content while the other consisted of young ash with a coarse texture and low phosphate absorption. Both of them display high exchangeable cation contents.
Bulusan soil in Sorsogon has a low pH, high exchangeable aluminum content and low base saturation.
Zambales soils derived from Mt. Pinutubo, Zambales province have a high pH, phosphate absorption, and coarse texture but low C.E.C. and water contents.
Negros soils found at high elevations of Mt. Canlaon, Negros Occidental, have a high pH, high organic matter content and phosphate absorption but low exchangeable cation content with indications of the presence of amorphous clay minerals.
From the relationships established between the phosphate absorption coefficients and base saturation of the samples, volcanic ash soils in the Philippines and thosefromJapan may be classified into two groups according to varying combinations in the range of these two properties.
Eighteen profiles were classified as Udol1, 2 profiles; Ochrept, 5 profiles, Andept, 9 profiles and Udult, one profile based on the Soil Taxonomy. Using lCOMAND, 10 of them were classified as Udand and Ustand. It was considered that the volcanic ash soils in the Philippines have undergone a transition through two types:
(1) Vitric Hapluudand → Pachic Hapluudand → Eutrochrept → Distrochrept → Hapludult,　and (2) Udivitrand, Vitric Hapludand, or VitricHapluustand → PachicHapludand →Hydric Melanudand.