1

Chapter 1

TERMINOLOGY, CONCEPTS AND GEOGRAPHIC DISTRIBUTION OF VOLCANIC ASH SOILS

S. SHOJI, R. DAHLGREN and M. NANZYO

1.1. TERMINOLOGY

The term “volcanic ash soils” is commonly used to designate soils formed from tephras or pyroclastic materials. Since most of these soils have unique properties inherited from or associated with the properties of tephra, the general term “volcanic ash soils” is often used to denote Kurobokudo (The Third Division of Soils, 1973), Andosols (FAO/Unesco, 1974), and Andisols (Soil Survey Staff, 1990, 1992). However, not all volcanic ash soils are Kurobokudo, Andosols or Andisols and vice versa. As described in Chapter 3, there are tephra-derived Spodosols, Inceptisols, Mollisols, Oxisols, etc., and there are some Kurobokudo, Andosols or Andisols formed from nontephritic materials such as volcanic rocks, sedimentary rocks, mixed materials of tephra and loess, etc.

A variety of soil names connotative of the volcanic ash soils have been proposed in Japan as follows: Volcanogenous loams (Seki, 1913), Prairie-like brown forest soils (Kamoshita, 1955), Volcanogenous soils (Yamada, 1951), Volcanogenous black soils (Uchiyama et al., 1954), Humic Allophane soils (Kanno, 1961), and Kurobokudo (The Third Division of Soils, 1973). The FAO/Unesco (1974) also lists several soil names to describe volcanic ash soils throughout the world: Yellow- brown loams and Yellow-brown pumice soils (New Zealand); Humic Allophane soils, Trumao soils (Chile); Acid Brown Forest soil, Acid Brown Wooded soil (Canada); Sols bruns tropicaux sur materiaux volcaniques (Zaire); Andosols (France); Andosols (Indonesia); Kurobokudo (Japan); Andepts (U.S.A.); Volcanic soils (former U.S.S.R.). It is interesting to note that soil names, such as “Andosols” and “Andepts” originated from “Ando soils”, while there is no Japanese soil name coined from the term “Ando” (An; dark: do; soils), because “Ando” is an uncommon Japanese word literally translated as “dark soil”.

“Ando soils” was first introduced in 1947 during the reconnaissance soil surveys in Japan by American soil scientists (Simonson, 1979). The principal characteristics of volcanic ash soils which were the basis for recognizing the new Ando great soil group in the intrazonal order (Simonson, 1979) are described below:

(1) The A1 horizons are usually thick and dark, and the soils lack the E horizons expected in Podzols. Amounts of organic matter in A1 horizons commonly range

2 S. SHOJI. R. DAHLGREN and M. NANZYO

up to 15% and reach 30% in the extreme cases. The C/N ratios of the organic matter range from 13 to 25.

(2) Where not cultivated, the soils are moderately to strongly acid with pH ranges of 4.5 to 5.1 in A horizons and 5.0 to 5.7 in deeper profiles. Levels of exchangeable bases are low, ranging from 2 to 9 cmol, kg-’ of soil material, whereas exchangeable Al (in M NH4C1) exceeds 3 cmol, kgg’ generally and ranges up to 8 cmolc kg-’.

(3) The silica-sesquioxide ratios of colloid fractions range from 1.3 to 2.0 in A horizons and from 0.75 to 0.90 in deeper profiles of these soils on Honshu. In Kyushu, the corresponding ranges in ratios are 0.4 to 1.13 in A horizons and 0.67 to 1.03 in deep profiles.

The term “Ando soils” appeared for the first time in the journal Soil Science in 1949 and then the Ando group was identified in widely separated regions of the world (Simonson, 1979).

Though the term “Ando soils” is still widely used, it was replaced by “Andepts (currently the Andisol order)” as a suborder of Inceptisols in Soil Taxonomy (Soil Survey Staff, 1975, 1990, 1992). A part of the original name “Ando soils” was retained in coining the new names of Andosols and Andisols.

1.2. CENTRAL CONCEPTS

The Japanese name “Kurobokudo” means black (Kuro) fluffy (boku) soils (do) and it has been traditionally used in Japan. The central concept for Kurobokudo includes the following (The Third Division of Soils, 1973, 1982):

(1) The parent material is volcanic ejecta. (2) The horizon sequence commonly shows dark-colored A horizons over brown

(3) The soil material is vitric and/or rich in allophane. (4) The allophanic soils have a low bulk density, a high exchange capacity, and

high phosphate adsorption. Andepts were recognized as immature soils (Inceptisols) that have not devel-

oped features diagnostic for other soil orders (Soil Survey Staff, 1975). The central concept can be summarized as follows:

to yellowish B horizons.

(1) The parent material is mostly pyroclastic material. (2) The soil material contains an appreciable amount of allophane and shows

(3) The soil material is mostly vitric. By comparing the two central concepts described above, it appears that the

central concept of Kurobokudo places emphasis on the existence of dark-colored A horizons while that of Andepts includes some nontephritic materials such as pyroclastic rocks, sedimentary rocks, or basic extrusive igneous rocks. Both of these concepts suggest that the unique chemical and physical properties are primarily attributable to allophane. Andosols described by Duchaufour (1982),

low bulk density, or

TERMINOLOGY, CONCEPTS AND GEOGRAPHIC DISTRIBUTION OF VOLCANIC ASH SOILS 3

FitzPatrick (1971), etc., have a central concept similar to that of Andepts. Before 1978, Andisols were regarded as soils dominated by allophanic mineral-

ogy. The discovery of Andisols with nonallophanic mineralogy by Shoji and Ono (1978) initiated a reevaluation of the central concepts of Kurobokudo, Andosols, and Andepts, because the nonallophanic soils share many of the unique chemical and physical properties exhibited by allophanic soils. The name “Andepts” was changed to “Andisols” in the Andisol proposal (Smith, 1978), and the central con- cept of “Andisols” was based on the presence of active forms of Al and Fe, such as the noncrystalline materials, allophane, imogolite, ferrihydrite or aluminum- humus complexes (Leamy et al., 1988).

As described above, there are many soil names referring to volcanic ash soils. However, none of them are defined as precisely as the Andisols described in Chapter 4.

1.3. GEOGRAPHIC DISTRIBUTION OF VOLCANIC ASH SOILS

The distribution of soils derived from volcanic materials closely parallels the global distribution of active and recently active volcanoes. Because of this association, the distribution of volcanic ash soils is geographically predictable. Volcanic ash soils cover approximately 124 million hectares or 0.84% of the world’s land surface (Leamy, 1984). Approximately 60% of volcanic ash soils occur in tropical countries. While volcanic ash soils comprise a relatively small extent of the world’s surface, they represent a very important land resource due to the disproportionately high human populations living in these regions as described in Chapter 8. This section briefly describes the geographical distribution of volcanoes and Andisols throughout the world.

1.3.1. Geographic distribution of volcanoes

The great majority of active and recently extinct volcanoes are concentrated in the circum-Pacific Ring of Fire. This ring includes many volcanoes in New Zealand, Melanesia, the Philippines, Japan, Kamchatka, Aleutian, Alaska, and the western coast of North America to South America (Bullard, 1984).

The volcanoes in the Pacific Ring of Fire are associated with geologically young or still growing volcanic mountains and show high explosion indices of approximately 80 percent (Katsui, 1978). Their rocks and tephras are mostly andesite belonging to the Calc-alkali-rock series. Thus, the volcanoes of this belt disperse andesitic tephras resulting in a wide distribution of Andisols or volcanic ash soils in their proximity.

The Alpine-Himalayan volcanic belt extends from the Canary and Madeira Islands through the Mediterranean region including Italy and Sicily, the Turkish- Armenian border and Mount Demavend in Iran. The volcanic belt reappears in Burma and is traced to Sumatra, Java and the Lesser Sunda Islands in Indonesia (Bullard, 1984). There are many active andesitk volcanoes along this belt.

4 S . SHOJI, R. DAHLGREN and M. NANZYO

Many active volcanoes occur in the vicinity of the Red Sea to central Africa being associated with the great Rift Valleys. They show a mean explosion index of approximately 40 percent and their ejectas are various alkali rocks characterized by high KzO content (Katsui, 1978).

About 17 percent of the known active volcanoes of the world occur within the true ocean basins (Bullard, 1984). The ejectas of these volcanoes are largely basalt and the explosion indices are very low (for example, 1-3 percent for basaltic volcanoes in Hawaii) (Katsui, 1978). Thus, the tephra dispersal of these volcanoes is not extensive and Andisols formed from these ejectas under perhumid, isohyperthermic conditions as in Hawaii are very rich in noncrystalline Al and Fe hydroxides, reflecting the high content of these elements in the parent material.

1.3.2. Andisols on a regional basis

Andisols are distributed preferentially in regions where active and recently extinct volcanoes are located as shown in the Map of “Major Soil Regions of the World” with a scale of 1 : 30,000,000 which has been prepared by Eswaran et al. (1992). This soil resources map is based on a recent map produced by FA0 in 1990. The mapping units are defined by the suborders of Soil Taxonomy and the temperature regime. Thus, the distribution of five suborders of Andisols such as Cryands, Xerands, Vitrands, Ustands and Udands are shown on the map.

The principal regions of the world where Andisols are found were summarized by Leamy (1984) as follows:

- In Europe: Italy, Sicily, Sardinia, France (Massif-Central). - In Afnca and the Indian Ocean: Kenya, Rwanda, Tanzania, Ethiopia, Camer-

oon, Malagasy, Reunion, Canary Islands, Uganda, Sudan, Zaire. - In America: Alaska, British Columbia, Washington, Oregon, California, Mex-

ico, Costa Rica, Panama, Honduras, Guatemala, El Salvador, Nicaragua, West Indies, Ecuador, Colombia, Peru, Chile, Argentina, Bolivia.

- In Asia and the Pacific: Hawaii, Aleutian Islands, Kamchatka, Japan, Korea, Micronesia, Philippines, Indonesia, Papua New Guinea, Solomon Islands, Vanuatu, Fiji, Samoa, Tonga, New Zealand.

Dudal et al. (1983) reported an estimate of the extents of Andisols in the major regions of the developing world as follows: 5,424,000 ha for Africa, 59,000 ha for southwest Asia, 7,353,000 ha for southeast Asia, 30,421,000 ha for South America, and 13,526,000 ha for Central America.

REFERENCES

Bullard, EM., 1984. Volcanoes of the Earth, 2nd revised edition. University of Texas Press, Austin. Duchaufour, P., 1982. Andosols. In: TR. Paton (translated), Pedology: Pedogenesis and Classification.

George Allen and Unrwin, London, Boston, and Sydney, pp. 196-210.

TERMINOLOGY, CONCEPTS AND GEOGRAPHIC DISTRIBUTION OF VOLCANIC ASH SOILS 5

Dudal, R., Haggins, G.M. and Pecrot, A., 1983. Utilization of soil resource inventories in agricultural development. Proc. 4th Int. Soil Classification Workshop, Rwanda, 2 to 12 June, 1981. Part 1: Papers, Al3OS-AGCD, Brussels, Belgium. pp. 6-17.

Eswaran, H., Bliss, N., Lytle, D. and Lammers, D., 1992. The 1 : 30,000,000 Map of Major Soil Regions of the World (in preparation).

FAO/Unesco, 1974. Soil Map of the World, 1 : 5,000,000. Vol. 1, legend. Unesco-Paris. FitzPatrick, E.A., 1971. Andosols. In: Pedology, A Systematic Approach to Soil Science. Oliver and

Kamoshita, Y., 1955. Principal soil types (great soil groups) in Japan. Soil and Plant Food, 1: 99-101. Kanno, I., 1961. Genesis and classification of main genetic soil types in Japan, I. Introduction and

Humic Allophane soils. Bull. Kyushu Agr. Exp. Sta, 7: 13-185 (in Japanese, with English abstract). Katsui, Y., 1978. Distribution of volcanoes. In: Volcanoes. Urban Kubota, No. 15, Osaka, pp. 30-40 (in

Japanese). Leamy, M.L., 1984. Andisols of the world, In: Congresco International de Suelos Volcanicos, Commu-

nicaciones, Universida de La Laguna Secretariado de Publicaciones, serie informes 13, pp. 368- 387.

Leamy, M.L., Clayden, B., Parfitt, R.L., Kinloch, D.I. and Childs, C.W., 1988. The Andisol proposal 1988, Final proposal of the International Committee on the Classification of Andisols (ICOMAND). New Zealand Soil Bureau, Lower Hutt, New Zealand.

Boyd, Edinburgh, pp. 165-167.

Seki, T, 1913. Zwei vulkanogene Lehms aus Japan. Landw. Versuch. Sta. 79/80: 871-890. Shoji, S. and Ono, T., 1978. Physical and chemical properties and clay mineralogy of Andosols from

Simonson, R.W., 1979. Origin of the name “Ando soils”. Geoderma, 22: 333-335. Smith, G.D., 1978. A preliminary proposal for the reclassification of Andepts and some Andic subgroups

Soil Survey Staff, 1975. Soil Taxonomy, A basic system of soil classification for making and interpreting

Soil Survey Staff, 1990. Keys to Soil Taxonomy, 4th edition. AID, USDA-SMSS Technical Monograph

Soil Survey Staff, 1992. Keys to Soil Taxonomy, 5th edition. AID, USDA-SMSS Technical Monograph

The Third Division of Soils, 1973. Criteria for making soil series and a list of soil series. The first

The Third Division of Soils, 1982. Classification of cultivated soils in Japan. Nat. Inst. Agr. Res., Japan. Uchiyama, N., Abe, K. and Tsuchiya, T, 1954. Research on soil types of arable land, Tochigi Prefecture.

Yamada, S., 1951. A method to survey volcanogenous soils and volcanogenous soils in Hokkaido. Bull.

Kitakami, Japan. Soil Sci., 126: 297-312.

(The Andisol proposal, 1978). New Zealand Soil Bureau, Lower Hutt, New Zealand.

soil surveys. USDA-SCS Agric. Handb. 436. U.S. Gov. Print. Office, Washington, D.C.

No. 19, Blacksburg, Virginia.

No. 19, Blacksburg, Virginia.

approximation. Nat. Inst. Agr. Res., Japan (in Japanese).

Bull. Nat. Inst. Agr. Sci., B3: 43-139 (in Japanese, with English abstract).

Hokkaido Nat. Agr. Exp. Sta., 4 4 1-93 (in Japanese)