MORPHOLOGICAL, PHYSICAL, AND CHEMICAL CHARACTERISTICS OF SOME VOLCANIC SOILS OF MT. GALUNGGUNG

Results of study on morphological, physical, and chemical characteristics of three pedons developed on volcanic materials of Mt. Galunggung, namely BM1, BM2, and BM3, showed that these pedons had a different stage of profile development. Pedon BM1 is dassified as undeveloped, BM2 is medium developed, and BM3 is strongly developed. This is mainly caused by differences in relative age of the parent rocks, and elevation. Although classified as undeveloped, the soil represented by pedon BMI, the youngest, has immediately been used by farmers for rice cultivation because of water abundance, and h i availability of P, and basic cations derived from weathering of easily weathered amorphous materials and minerals. According to the Soil Taxonomy system of the USDA (Soil Survey Staff, 1996), pedons BMI, BM2, and BM3 are classified as Typic Udipsamment, Tapsha Hapludandic Typic Tmpdhent, and Hwnic ~ I Yres,pecti vely. Whitst, according to FAOtUNESCO system (1988), these pedons are dassified as Ed& Regosol, Eubic Regosol and Humic Alisol, respectively.


INTRODUCTION
Soils developed on volcanic materials usually have distinctive properties which in many parts of the wor1d are reflected in extremely high crops productivity, sometimes significantly associated with some of the world's highest human carrying capacity (Leamy, 1984), such as those developed in Java Island (Sutanto, 1988).The most important diagnostic features of volcanic ash derived soils include variation in chemical composition, specific morphologic features and the presence of some specific minerals such as short range order minerals, i.e. allophane, imogolite and some oxides (De Coninck, 1990).
According to FAO/UNESCO (1974), volcanic materials constitute the parent material of many different soils.Volcanic material derived soils have been classified in many countries: as Andosols, Regosols, and Latosols in Indonesia (Pusat Penelitian Tanah, 1976); Allophane soils and Kuroboku soils in Japan; Alluvial or Yellowish Brown Loam in New Zealand; as Andosols by FAO/ UNESCO (1974) and Andisol by Soil Survey Staff (1996).
In Indonesia, a group of soils derived from volcanic materials is widely spread over the archipelago, from Sumatera in the west over Java to Lesser Sunda Islands in the east (Tan, 1965), and covers about 20 millions hectares or about 10.4 % of the total land area (Pusat Penelitian Tanah, 1976).Most of food crops production in Indonesia are derived from these soils.Unfortunately, documentation or studies on these very important soils are very ra.re.
B. Mu/yanto.1999.J./1.This paper presents results of study on morphological, physical, and chemical properties of different volcanic materials derived soils of Galunggung Volcano in West Java and their cla~cation.

PHYSICAL ENVIRONMENT
Some physical environmental factors strongly determine characteristics of a soil.The most important factors are geology, topography, climate and landuse.The geological factors are related to the properties of parent materials.Topographic position of the soil is related to the water regimes, which influence the weathering processes, and physical and chemical properties.The climate and landuse also determine the weathering processes.

Geology
Mt. Galunggung is located at about 1'15' South Latitude and 1 08°03' East Longitude which covering an area in part of Garut and Tasikmalaya districts, West Java.The eruption activities of this volcano were reported in 1822, 1894, 1918, and 1982(Escher, 1920;;Bronto, 1982).From these eruptions, young deposits were built on the ruin of old deposits from eruptions before 1822.

Climate
The climate of Java is significantly characterised by a distinct wet and dry seasons.This season type is well pronounced in East and Central Java and less pronounced in West Java (Table 1).
Rainfall almost occurs over the whole year.Minimum rainfall coincides with the monsoon months, that are in June, July and August.The annual rainfall is higher than 3.000 mm.The average annual temperature is generally 24.5°C and the temperature is fair1y uniform during the whole year with a variation that never exceeds 2°C.Generally speaking, the mean monthly relattve humidity does not vary greatly and is always higher than 80 % due to high rainfall.The highest peak values of potential evapotranspiration is found in March and the lowest one in July.
According to Soil Taxonomy (1996), the investigated soils have udic moisture regime and isohyperthermic temperature regime.

Vegetation and land use
Not much of original vegetation is left in this area.They are mostly found on the top of volcanoes and mountains as protection forest areas.Areas unsuitable for agriculture are used for production forest of Swietenia macrophylla, Pinus merkusii, and Albizia fa/cataria or used as reforestation and agroforestry areas.The landuse for farming of the study area is mostly irrigated rice field, particular1y on the northern and eastern footslope.Since there exist no limitation of water, the cropping pattern varies from continuous rice (3x with short age cultivar or 2x rice of medium age cultivar) to 1 x rice and secondary crops or another pattern depending on the market demand.In area where irrigation is not possible, rainfed agriculture is the dominant land use type with a great variety of crops planted in various combinations.

Material
The three selected pedons are located in locations near Singapama, Sukajadi and lndihiang of the Mt.Galunggung area, Tasikmalaya, West Java (Figure 2).They were selected on the basis of the Soil Map of West Java, at scale of 1 :250 000 prepared by Pusat Penelitian Tanah (1976).
Soil samples were taken from every identifiable horizon of the selected pedons.Two kinds of soil samples were collected: bulk samples for routine physico-chemical analysis and undisturbed soil samples for physical analysis.

Methods
The routine physico-chemical analysis was carried out mainly according to the methods described in "Procedure for Soil Survey" (1984) except for granulometric analysis.All data were reported on the basis of the < 2 mm material.
This paper presents results of study on morphological, physical, and chemical properties of different volcanic materials derived soils of Galunggung Volcano in West Java and their claiSification.
PHYSICAL ENVIRONMENT Some physical environmental factors strongly determine characteristics of a soil.The most important factors are geology, topography, climate and landuse.The geological factors are related to the properties of parent materials.Topographic position of the soil is related to the water regimes, which influence the weathering processes, and physical and chemical properties.The climate and landuse also determine the weathering processes.

Geology
Mt. Galunggung is located at about t>15' South Latitude and 1 08°03' East Longitude which covering an area in part of Garut and Tasikmalaya districts, West Java.The eruption activities of this volcano were reported in 1822, 1894, 1918, and 1982(Escher, 1920;;Bronto, 1982).From these eruptions, young deposits were built on the ruin of old deposits from eruptions before 1822.

Climate
The climate of Java is significantly characterised by a distinct wet and dry seasons.This season type is well pronounced in East and Central Java and less pronounced in West Java (Table 1).
Rainfall almost occurs over the whole year.Minimum rainfall coincides with the monsoon months, that are in June, July and August.The annual rainfall is higher than 3.000 mm.The average annual temperature is generally 24.5°C and the temperature is fair1y uniform during the whole year with a variation that never exceeds 2°C.Generally speaking, the mean monthly relattve humidity does not vary greatly and is always higher than 80 % due to high rainfall.The highest peak values of potential evapotranspiration is found in March and the lowest one in July.
According to Soil Taxonomy (1996), the investigated soils have udic moisture regime and isohyperthermic temperature regime.

Vegetation and land use
Not much of original vegetation is left in this area.They are mostly found on the top of volcanoes and mountains as protection forest areas.Areas unsuitable for agriculture are used for production forest of SWietenia macrophy/la, Pinus merkusii, and A/bizia fa/cataria or used as reforestation and agroforestry areas.The landuse for farming of the study area is mostly irrigated rice field, particular1y on the northern and eastern footslope.Since there exist no limitation of water, the cropping pattern varies from continuous rice (3x with short age cultivar or 2x rice of medium age cultivar) to 1 x rice and secondary crops or another pattern depending on the market demand.In area where irrigation is not possible, rainfed agriculture is the dominant land use type with a great variety of crops planted in various combinations.

Material
The three selected pedons are located in locations near Singapama, Sukajadi and lndihiang of the Mt.Galunggung area, Tasikmalaya, West Java (Figure 2).They were selected on the basis of the Soil Map of West Java, at scale of 1 :250 000 prepared by Pusat Penelitian Tanah (1976).
Soil samples were taken from every identifiable horizon of the selected pedons.Two kinds of soil samples were collected: bulk samples for routine physico-chemical analysis and undisturbed soil samples for physical analysis.

Methods
The routine physico-chemical analysis was carried out mainly according to the methods described in "Procedure for Soil Survey" (1984) except for granulometric analysis.All data were reported on the basis of the < 2 mm material.The granulometric analysis was carried out by sieving and sedimentation.The particle size distribution of fraction <2mm analysis was done with H 2 ~ 30 % to remove organic matter by successive sedimentation after• treatment.The sand fraction was separated by wet sieving using a 50 J.Ull sieve.Separation of clay and silt was carried out by successive sedimentation.The clay was siphoned and collected after 8 hours and 35 minutes from the suspension from 10 em depth.
The percentage was calculated on the dry weight basis, following the size classes of USDA and textural classes according to International classification (Soil Survey Staff, 1996).Stratigraphically, the Qta unit is the youngest, since it was due to the eruption of 1982.The pedons 8M1 and 8M2 are situated above 500 m asl, 8M3 below 500 m asl.The footslopes of volcanoes have been dissected, giving rise to a gently to rolling landscape at lower altitude, passing over into rolling and hilly at higher altitude.

Figure 2. The location of soil profiles
The recent soil on Qta is a Grey Regosol (BM1).
On the older deposits situated at higher altitude the soil is Andosol (8M2) while profile 8M3 on the oldest deposit and at lower altitude fonns a Reddish Brown Latosol.Due to repeated eruptions and sedimentation, the pedons display a composite morphology and several buried soils may be present underneath the present day profiles.Various types of land utilisation are recognised in these areas: gently sloping to level terrain have been transformed into irrigated rice field while the undulating to rolling land Is used for dry land agriculture.The hilly to mountainous terrain are mostly for agroforestry.

Morphological properties
Pedon BM1 is located on a recent volcanic alluvial plain at the eastern footslope of Galunggung, about 550 m asl.The terrain is level, without evidence of erosion.The profile has no horizon differentiation, sandy, massive and strudur1ess, finn, and no root development.
These sandy soils are mined for building construdion and afterwards they are transfonned into paddy rice fields.Pedon BM2, located in Kampung Sukajadi Linggawangi, Leuwisari distrid, Tasikrnalaya is situated in hilly terrain on the southern convex slope of Mt.Galunggung, at about 750 m asl .. The upper layers I to IV are recent and have little or no development.Layer V is an older soil.The soil is mostly sand to sandy loam, alternating massive and loose strudureless in the layers I to IV, but layer V is weak, fine subangular blocky, very friable and finn consistence In the range of very dark brown to dark yellowish brown.
This area is dominated by dryland agriculture.Terracing and mixed fanning are applied without fertilization.
Pedon BM3, located in Cigalontang village, Tasikrnalaya is observed on the middle slope of a hill on the Southern lower footslope of Mt.
Galunggung.The evidence of erosion is moderate.This soil is relatively deep and well drained.
The colour changes from dark grey brown in the A horizon through reddish brown in the E and Bt1 horizons to strong brown in the Bt2 and the Bt3 horizons.The texture is clay throughout, and very weak patchy cutans are noticed in the Bt2 and Bt3 horizons.The structure is moderate-medium granular in the A horizon, gradually changes into weak medium subangular blocky in the E, Bt1 and Bt2 horizons, and to moderate medium subangular blocky in the Bt3 horizon.The consistence in moist condition is friable in the A, E, and Bt1 horizons and gradually changes to finn and very finn in the Bt2 and Bt3 horizons.The material is plastic to very plastic.Root development is up to 90 em depth.The land utilisation is mostly agroforestry.Paddy rice field is found only where water is available.

Physical and Chemical Properties
The physical and chemical analysis data are presented in Table 2. and Table 3.
The samples of the young volcanic soil (BM1) disperse in alkali solution.The particle size distribution is dominated by sand fraction.Textural class of the horizons ranges from sand to loamy sand.The bulk density has not been detennined.The soil reaction is acid in H 2 0 and pH KCI is 0.6-1.1 units lower than the pHH 2 0. These feature has been assumed to express a net negative charge of the exchange complex throughout the profile (Tan, 1982).The organic carbon content seems very tow (0.11-0.88 %) and shows an irregular distribution with depth.The low content of nitrogen is related to the low content of organic matter.The high amount of available P is a result of weathering of volcanic glass and fluoroapatite microcrystals which nonnally occurs as an accessory mineral or as an inclusion of ironbearing minerals in all types of eruptive rocks (Prinz et.a/., 1978)  (1.18-4.73o/o) and base saturation are low (4.41-14.64%).The samples of the old volcanic soil (BM3) disperse with nonnal dispersing agent and particle size distribution is dominated by the clay fraction ranging between 50.01 to 88.28 %.The clay content increases with depth.Bulk density is higher than 0.9 glee.
The pH H 2 0 is acid, ranging from 5.0 to 5.7.The pH KCI is lower than pH H 2 0 with a difference in the range of 1.2 to 1.4 units.Organic carbon content decreases with depth and ranges from 0.25 to 2.29 %.The totai-N is low (0.4-0.14 %) and the available-P is mostly not significant.The sum of cations is relatively high (7.28-10.36me/1 OOg} and is dominated by calcium, while the NH 4 0ac CEC pH 7 is medium (22.84 to 26.96 me/100g).Therefore, the base saturation is also medium (30.01-45.36%).
Pedon BM2 (Yellowish Brown Andosols).The soil has an ochric epipedon, < 35 o/o rock fragments and sand to sandy loam texture.The profile can be divided into two parts, the upper part is a soil without profile development and the buried part is soil with andic properties.The base saturation is higher than 50% in the upper soil but less than 50% in the buried soil.This soil is classified as Taptho Hapludandic Typic Troporthents, sandy loam, isohyperthennic (Soil Survey Staff, 1996), or as Eutric Regosol (FAO/UNESCO, 1988).1996), and Humic Aliso/ (FAOIUNESCO, 1988).The morphological, physical and chemical characteristics described above suggest that three pedons of the studied soils have different development.Pedon 8M1 is Typic Udipsamment, 8M2 is Taptho Hapludandic Typic Troporthent, and 8M3 is Humic Hapludult.This different stages of development is mostly caused by different relative ages of the parent materials, besides that the elevation difference also plays a roll.As mentioned ear1ier, the parent material of pedon BM1 is the youngest and that of 8M3 is the oldest; hence pedon 8M3 has a stronger development • than the others and pedon 8M1 has the weakest.
Comparison of pedons 8M3 and 8M2 shows that below 500 m asl (8M3) no andic properties are present, while above soom asl (8M2) the andic properties are well developed.This is probably due to the clear1y temperature influence at both elevations with causes difference in organic matter accumulation in both profiles.transform this sandy soil into paddy rice field.This seems an appropriate decision, because the chemical analysis showed that the available-P and available basic cations in this soil are high.However, they have to add nitrogen fertiliser because nitrogen content of this soils is very low.
In the older classification system is pedon 8M3 classified as Latosol.According to Mohr, et a/.
(1972) Latosols are included in Oxisols without plinthite.Macro and micro morphological analyses show that this pedon seems to be an Oxisol, but mineralogical and chemical analyses show that the weatherable minerals and also the CEC NH40Ac pH7 of clay are still too high for the oxic horizon requirement.Hence, pedon 8M3 is classified as Ultisol (Humic Hapludult).

CONCLUSIONS
The morphological, physical and chemical characteristics of three pedons developed on the volcanic materials of Mt.Galunggung show that these three pedons have different profile developments.The pedon 8M1, 8M2 and 8M3 have no development, medium development and strong development respectively.This different stages of development is mostly caused by different relative ages of the parent materials, and the elevation difference.
According to the Soil Taxonomy (Soil Survey Staff, 1996)

Figure 1 .
Figure 1.Geology of the studied area derived from quaternary deposits have developed on the complex of Galunggung volcanoes: 8M1 on the Qta unit, 8M2 and 8M3 on the QGjp and Qlh2 unit.

Table 1 .
Climatic Data of Tasikmalaya, West Java . The CEC of this soil is very low because it has a very small colloidal fraction.The texture is dominated by sand: 73.62-95.74o/o in the upper layers and 58.94-63.97% in the buried soil.The bulk density is high in the upper layers but about 0.9 in the buried one.Organic carbon (0.15-2.7 o/o) and nitrogen (0,02 %) are very low.OOgr) and the sum of extractable cations The layers I to IV of profile 8M2 show a no clear evolution and the buried soil behave in a different way.The samples of the upper layers disperse with nonnal dispersing agent whereas the buried one seems to disperse in acid conditions.