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IndonesianSoil properties Journal of the of eastern Agricultural toposequence Science of4(1) Mount 2003: Kelimutu 1-11 1 SOIL PROPERTIES OF THE EASTERN TOPOSEQUENCE OF MOUNT KELIMUTU, FLORES ISLAND, EAST NUSA TENGGARA AND THEIR POTENTIAL FOR AGRICULTURAL USE Hikmatullah, H. Subagyo, and B.H. Prasetyo Indonesian Center for Soil and Agroclimate Research and Development Jalan Ir. H. Juanda No. 98, Bogor 16123, Indonesia ABSTRACT 15,000 ha. Its caldera has three-colored lakes, i.e., dark red, green, and bluish colors. The color always changes Kelimutu stratovolcano is one of the young volcanoes exten- with season, making it an interesting tourism site. To sively found in Flores island. Studies on volcanic soil properties date, studies on soil properties and their suitability and their suitability for agricultural development in the whole for supporting agricultural development of the whole island are lacking. The research was conducted to evaluate the relationship of elevation and soil properties, and suitability for island are lacking. agricultural development. Five representative pedons at eleva- Soils of the Kelimutu were developed from andesitic tion of 550, 1,000, 1,200, 1,400, and 1,600 m above sea level volcanic rocks, and dominantly grouped into Andi- (asl), respectively, were studied in the field, and 22 soil samples sols, Mollisols, and Inceptisols (Hikmatullah et al. were analyzed in the laboratory. The results indicated that 1997). According to Suwarna et al. (1990), Kelimutu elevation significantly affected soil properties and degree of volcano had been erupting and collapsing, as shown soil weathering. With decreasing elevation, sand content, amorphous material content, and phosphate retention de- by the formation of three-lake calderas. The erupted creased. Concomitantly, clay content, H2O-pH, exchangeable materials were composed of lava, breccias, agglomer- Ca and Mg, base saturation, and soil-CEC increased. A highly ate, ash and sandy tuffs, all of andesitic to basaltic positive correlation was shown between P retention and NaF- composition. Shoji et al. (1975) reported that andesitic pH, Al, and (Al+0.5 Fe) contents extracted by acid ammonium and basaltic volcanic rocks were composed of SiO2 as oxalate. Soil-CEC also showed significant positive correlation with clay and silt contents, organic carbon, and exchangeable much as 53.5-62% and 45-53.5%, respectively. Mineral Ca and Mg. Degree of weathering increased with decreasing assemblage consists of plagioclase-andesine, pyro- elevation as reflected by decreasing silt/clay ratio. Soils de- xenes, hypersthenes, augite, and olivine. From the veloped from Entisols (Lithic Udorthents) at 1,600 m asl, to landform view, the landscape of Kelimutu may be Andisols (Typic Hapludands) at 1,000-1,400 m asl, and divided into summit, volcanic upper slopes, middle Mollisols (Typic Hapludolls) at lower elevation down to 550 m slopes, and lower slopes (Hikmatullah et al. 1997). asl. Soils at 1,400-1,600 m asl are unsuitable for agriculture. Soils at 1,000-1,200 m are moderately suitable for food crops, The soil study following a toposequence is useful horticulture, and estate crops. Dominant limiting factors are to understand the change of physical, chemical, and steep slopes and P retention. Soils at 550 m asl are suitable for mineralogical soil properties with increasing eleva- food and estate crops, and also lowland horticulture. tion, and to assess their suitability for crop develop- [Keywords: Soil chemicophysical properties, mineral content, ment. Subardja and Buurman (1980) studied a topo- soil classification, land suitability, East Nusa Tenggara] sequence of soils derived from andesitic volcanic materials of the Gede-Pangrango volcanoes in the humid Puncak-Bogor-Jakarta area, and the results INTRODUCTION showed that elevation influenced soil properties, degree of weathering, and soil development. With Flores island, with a total area of 1.42 million ha is one decreasing elevation, soil sequence was found chang- of the major islands in East Nusa Tenggara Province. ing from Andisols to Inceptisols, and became Oxisols The southern part of the island, from west to east, is in the low elevation. Down to lower elevation, the dominated by volcanic landform and about 32% is soils became more weathered and developed, and made up of young volcanoes, a few of them are still leaching of bases/nutrients was more intense. Similar active. One of these young volcanoes is Mount results were also reported by Van Schyulenborgh Kelimutu in the Ende regency, a stratovolcano having (1957) and Subagyo et al. (1997) in a toposequence of the peak of 1,650 m asl, with a total area of about soils at various elevations of volcanoes in West Java. 2 Hikmatullah et al. Subagjo and Buurman (1980) studied a soil catena and soil moisture content (water contents at 33 kPa developed from andesitic volcanic materials under minus those at 1,500 kPa water retention). Chemical relatively dry climate condition on the western slope analyses included pH (in H2O and NaF solution), of Lawu volcano. They found that the soil sequence organic carbon, potential P2O5 and K2O contents by starting from the highest elevation was Andisols- HCl 25% extraction, exchangeable bases (Ca, Mg, K, Inceptisols-Alfisols-Vertisols. Na) and soil cation exchange capacity (soil-CEC) by This study aimed to evaluate the relationship be- 1N NH4OAc pH 7.0 extraction, base saturation (per- tween elevation and soil physical, chemical and centage of sum of exchangeable bases relative to mineralogical properties in relation to degree of soil CEC), P retention by Blakemore et al. (1981), Al and weathering in a toposequence, and soil suitability for Fe contents extracted by acid ammonium oxalate, crop establishment to support agricultural develop- defined as amorphous aluminum (Alo) and amorphous ment. iron (Feo) (Ping et al. 1988). Mineralogical composition of sand mineral fraction was determined by line counting method using pola- MATERIALS AND METHODS rization microscope. Clay mineral composition was determined using X-ray diffractometer (XRD), with Climate and Vegetation standard saturation of Mg and K saturation plus heating to 550oC. Methods of analyses followed the The study area has a humid tropical climate. The standard procedures described in Soil Survey Labo- mean annual rainfall is 1,508 mm in the lowland of ratory Methods Manual (Soil Survey Laboratory Staff Ende (20 m asl), and becomes higher with increasing 1991). Regression analysis was used to analyze the elevation, i.e. 3,700 mm at Detusuko (650 m asl). correlation between some important soil properties. Rainfall type according to Schmidt and Ferguson The studied pedons were classified according to Soil (1951) is classified as C (relatively dry) at lowland, Taxonomy (Soil Survey Staff 1998) at subgroup level. and A (very wet) at higher elevation. Soil moisture The soil suitability for food crops, horticulture, and regime changes from ustic at lowland to udic at Detu- estate crops was determined using the criteria out- suko and higher elevation. Air temperature decreases lined by Djaenudin et al. (2003). with increasing altitude, from mean monthly of 27.7oC at Ende, 23.0oC at Detusuko, to 20.3oC at highland (Hikmatullah et al. 1997), therefore soil temperature regime also changes from isohyperthermic to iso- RESULTS AND DISCUSSION thermic. The present landuse of the area was com- posed of maize and sweet potatoes in the lower slope, Physical Properties horticultural crops, i.e., cabbage, potatoes, and carrot Downslope with decreasing elevation, as sand con- in middle slope, and pine forest in upper slopes and tent decreased, clay content significantly increased summit area of the volcano. (Table 2). The increasing clay content feature can be used as an indicator for increasing degree of weath- Soil Sampling ering. Van Wambeke (1962) used silt and clay ratio to Five representative pedons at the eastern topo- estimate the degree of weathering of soil pedon, and sequence of the volcano, at elevation of respectively postulated that the lower the ratio, the higher the 1,600, 1,400, 1,200, 1,000, and 550 m asl were selected degree of weathering. By increasing weathering, the for the study (Fig. 1). The description of soil morpho- silt fraction changed into clay fraction so that clay logical properties in the field was carried out follow- content increased, thus the silt and clay ratio was to ing the guideline outlined by FAO (1990). As much as be lower. 22 soil samples from each horizon of each pedon were Particle size distribution data showed that as selected for physical, chemical, and mineralogical elevation decreased, sand fraction consistently analyses in the laboratory (Table 1). decreased, silt fraction more or less constant, and the clay fraction significantly increased. As a result, silt and clay ratio (Table 2) consistently became smaller Laboratory Analyses with decreasing elevation. Therefore, it may be Physical analyses consisted of particle size distribu- concluded that the degree of soil weathering in- tion (three fractions) using Pipette method, bulk creased with decreasing elevation. With decreasing density at 33 kPa water retention, total pore space, elevation, particle size class became finer and finer, Soil properties of the eastern toposequence of Mount Kelimutu 3 Fig. 1. Location of the studied pedons, Ende regency, Flores island, East Nusa Tenggara. Table 1. Distribution of pedons and soil samples on toposequence of Mount Kelimutu, East Nusa Tenggara. Pedon Elevation Slope gradient Dominant landuse Number of number (m asl) (%) sample K-1 1,600 38 Pine forest 2 K-2 1,400 32 Pine forest and shrub 5 K-3 1,200 22 Shrub and pine forest 5 K-4 1,000 20 Maize, horticulture 5 K-5 550 18 Cassava, sweet potatoes 5 that was, gradually changed from coarse-loamy to density became higher (0.68 and 1.01 g cm-3 vs. 1.14 fine loamy, and eventually fine or clayey. These find- and 1.18 g cm-3), total pore space was smaller (74 and ings are in agreement with the results reported by 62% vs.

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