Tropical Volcanic Soils From Flores Island, Indonesia

ABSTRACT


INTRODUCTION
In Indonesia, the volcanic soils have a total area of 5.4 millions ha or 2.9% of the total Indonesia archipelago (Subagjo et al. 2004), whereas in the world the soils occupy about 0.84% of the earth's surface (Leamy, 1984;Takahashi and Shoji 2002).The volcanic soils have widely distributed along a belt in islands of Sumatra, Java, Bali, Nusa Tenggara, Celebes, and Halmahera.The investigation of the volcanic soils in Indonesia was initiated by some researchers, such as Van Schuylenborgh (1957), Dudal and Soepraptohardjo (1960), and Tan (1965).Some studies of the volcanic soils in last decade have been reported, especially from Sumatra (Fiantis and Van Ranst 1997;Alkasuma and Badayos 2003), Java (Arifin and Hardjowigeno 1997;Van Ranst et al. 2002;Fauzi and Stoops 2004;Yatno and Zauyah 2008), North Sulawesi (Hikmatullah 2008), and Dompu Sumbawa (Sukarman et al. 1993).
Soils that are developed on volcanic parent materials of Quarternary age have important role, due to unique morphological, physical, chemical and mineralogical properties and high potential for agricultural development to produce many kinds of agricultural commodities.The volcanic soils, in most cases are classified into Andisols order but not all volcanic soils are Andisols, depend on the weathering stage and soil forming processes (Shoji et al. 1993).Many studies of the volcanic soils have been reported from certain countries, such as from Japan (Shoji and Ono 1978), United States (Wada et al. 1986;Shoji et al. 1988), Mexico (Prado et al. 2007), Ecuador (Zehetner et al. 2003;Buytaert et al. 2007), Costa . Rica (Nieuwenhuyse et al. 1993), New Zealands (Parfitt et al. 1983), Portugal (Madeira et al. 1994), Greece (Moustakas and Georgoulias 2005) and Rwanda Africa (Nizeyimana 1997).
Soil resources of the Flores Island with a total area of 1.4 M ha had been documented in reconnaissance level.About 0.45 Mha of the soil resources was developed from volcanic parent materials, and dominantly grouped into Andisols, Mollisols and Inceptisols orders (CSAR 1997).The composition of sand mineral fraction of the volcanic materials consists of plagioclase, andesine, pyroxene, hypersthene, augite and olivine (Suwarna et al. 1990;Kusumadinata et al. 1981).
The main characteristics of the soils developed from volcanic materials, such as Andisols, have unique characteristics, such as dark color in the topsoils, high content of organic materials, low bulk density, high porosity, high P retention, high content of acid ammonium oxalate extractable Al, Fe and Si (Al o , Fe o , Si o ), and high weatherable minerals reserve (Shoji et al. 1993;Nanzyo 2002).In general, the Andisols order are found in high plain (>700 m asl.), but it also found in low plain, such as in North and West Sumatra, as reported by Tan (1998).Andisols should meet the requirements for andic soil properties.
The andic soil properties are based on soil physical, chemical, and mineralogical properties, consisting of sand content, bulk density, P retention, content of (Al o +0,5Fe o ) extractable ammonium oxalate, and volcanic glasses (Soil Survey Staff 2006).
The objective of the study was to characterize the andic properties of the soils which were originated from the parent materials of five volcanoes with different climatic conditions in Flores Island, Indonesia.The characterization were executed according to the methods and criteria of the Soil Taxonomy (Soil Survey Staff 2006).

Study Area
There are five soils profile from five different locations that had been observed their characteristics (Table 1).The soils were taken from Flores Islands, eastern part of Java and Bali islands.Flores island, Indonesia, with a total area of 1.4 millions ha, is located at coordinate of 08°10'-09°05' South Latitude, and 119°45'-123°10' East Longitude, with elevation of 0-2,350 m above sea level.The location of soil profiles is presented in Figure 1.(Schmidt and Ferguson 1951).Calculated water balance using Newhall Simulation M odel (Wambeke et al. 1986) showed udic soil moisture regime in the western part and ustic soil moisture regime in the eastern part.The soil temperature regime belongs to isohyphertermic for the area less than 1,000 m and isothermic for area more than 1,000 m above sea level.

Methodology
In generally, the soil profiles were compared, following the differences in their lithological characteristics (parent material) including their occurrences.The studied profiles were examined according to their climatic condition (annual rainfall).
Samples were air-dried, crushed and sieved to pass a 2 mm sieve.In the fine earth fraction, the sand fraction was determined by wet sieving, and the silt and clay fraction using the pipette method.Bulk density (BD) was determined in 33 kPa and 1,500  (Burt 2004).
To test amorphous materials and andic soil properties, soil pH in 1M NaF was measured at 1:50 after exactly 60 minutes.Phosphate retention was determined using the method of Blakemore et al. (1987).Dissolution analyses were conducted for acid ammonium oxalate extractable Al, Fe and Si (Al o , Fe o , Si o ), and ammonium pyrophosphate extractable Al and Fe (Al p , Fe p ) using the method of Blakemore et al. (1987).
Mineral composition of sand fraction was determined by line counting method, using polarization microscope (Buurman 1990).The clay fraction analyses used X-Ray Diffraction (XRD) with standard treatment of Mg 2+ saturation.Soil classification was determined using the Keys to Soil Taxonomy (Soil Survey Staff 2006) at subgroup level.
For the purposes of the study, five selected profiles from the above volcanoes were described in the field, and soil samples were taken by horizons for physical, chemical and mineralogical analyses in the laboratory.The distribution of the profiles and Station Elev.
their environments are presented in Table 1 and Figure 1.

Morphological Properties
All the soil profiles had deep solum (>100 cm) with variation of A horizon from 15 to 32 cm, and B horizon more than 75 cm (Table 3).The A horizon of profile P4 and P5 is thinner than the others which is probably affected by agriculture use.The color of A horizon is very dark brown (10YR2/1-3/3) to dark grayish brown (10YR4/2).While the B horizon have lighter color to dark brown (10YR3/4) to brown (10YR4/6), except for profile P2 has very dark brown (10YR2/1).
The darker color in A horizon than in B horizon is related to higher content of organic materials in A horizon.The horizon sequences of all the profiles were characterized by A umbric epipedon, Bw cambic diagnostic horizons, and C horizons, as A-Bw-C.The  Texture class: L =loam; SL = sandy loam; SCL = sandy clay loam: SiL = silt loam; SiCl = silty clay loam; LS = loamy sand, 2) Structure development grade: 1 = weak; 2 = moderate; size vf = very fine; f = fine; m = medium; c = coarse; shape: g = granular; sb = subangular blocky.horizon sequence indicated that the soils have moderate profile development (Van Ranst et al. 2002).
The A and B horizons of the profiles show weak structural development, indicated by subangular blocky breaking to fine if pressed by hand, and have very friable to friable consistency in moist condition.The friable properties have benefits in agricultural use, because of it easy to tillage and better roots development.The smeary or thixotropic properties, as an indication of high content of amorphous materials are significant in profile P1 and P2, but not clear in other profiles.This may be affected by high sand content indicating the parent materials have not yet much weathered.The profiles showed little different morphological properties, where the soil profiles from the western region (profile P1 and P2) are more developed than the eastern region.

Physical Properties
The soil profiles showed variation in silt and sand content.The soil texture varies from silt loam, loam, sandy loam and loamy sand that classified as medium to slightly coarse classes (Soil Survey Division Staff 1993).The sand distribution varies from 23 to 72% in A horizon, and from 12 to 80% in B horizon.On the contrary, the clay content is low, varies from 4 to 27% in A horizon, and from 9 to 30% in B horizon.It is clear that the soil texture of the soil profiles from eastern Flores Island has high sand content (sandy loam to loamy sand), while in the western it is high silt content (silt loam).The high sand content indicated that the soil has lower weathering stage as showed in structur al development features.Niuwenhuys et al. (1993) reported that in wet tropical climate in Costa Rica, the formation of Andisols from sandy volcanic materials need of time as long as 2000 years.But Wada (1985) mentioned that the formation of Andisols with full horizons of A-Bw-C in wet climate in Japan need a time at least 1000 years.The soils from volcanic materials with high sand content were similar to the volcanic materials found in Mt.Soputan, North Sulawesi (Hikmatullah 2008) and Mt.Kimangbuleng in Flores Island (Sukarman et al. 1999).
The bulk density (BD) has variation from 0.37 to 0.91 g cm -3 , both in A and B horizons.The low BD values meet one of the requirements of andic soil materials for the first group in Soil Taxonomy (Soil Survey Staff 2006).The amorphous material, i.e. allophone is one of the most important non-crystalline materials contributing to the low bulk density of the soils through the development of porous soil structure (Nanzyo et al. 1993).The high total pore spaces for all the soils profiles were also contribute to low bulk density.The content of available water percentages was higher in the subsoils than topsoils, that it may be related to large amount of organic matter and allophone content.

Chemical Properties
The organic carbon content of the soil profiles is generally high in A horizons and decrease to B horizons (Table 4).In A horizon the organic carbon content varied from 2.67 to 9.24% as classified as high.But in B horizons the organic carbon content varied from 0.31 to 7.37% as classified as low to high.
In general, the value of soil-pH H2O varied from 5.1 to 6.6 in A horizons, and from 5.3 to 6.6 in B horizons, as classified as relatively high, except for soil profiles P1 and P4 is more acid.The relatively high soil pH is benefit for crop growth, because of available soil nutrient and favorable for the growth.The relatively high pH in profiles P2, P3, and P5 may be caused by the nature of parent materials that not much yet weathered, and lower amount of rainfall that leaching bases are not intensively occurred.
The exchangeable bases (Ca, Mg, K, and Na) were generally dominated by high content of Ca and Mg that classified as low to medium.The content of bases reflected that the soils contain of nutrient bases that caused of higher pH (> 6.0).The base saturation varied from low to high (28-78%), except for profile P1 is very low (4-10%) indicating intensive leaching due to highest rainfall in western Flores Island.
The soil cation exchange capacity (CEC) is vary from low (<16 cmol c kg -1 ) to high (>24 cmol c kg -1 ) both in A and B horizons.The low soil CEC is probably caused by low content of clay and high of sand, especially in profile P3, P4 and P5.

Andic Properties and Soil Classification
The requirements for andic soil properties according to Soil Taxonomy (Soil Survey Staff 2006) can be grouped into 2 groups.The soils have to be classified as andic soils if meet one of the following groups.The first group is having: (a) Organic C content < 25%, (b) BD < 0.90 g cm -3 at retention 33 kPa, (c) P retention > 85%, and All the profiles have P retention > 85%, that meet the requirements of the second group, except for profile P5.The high P retention is close related to capability of soils to fix phosphate in adsorption complex; therefore the P nutrient may not be available to plant.
The content of Al o is very high for profile P1 and P2, with variation from 25.99 to 53.84%, and from 0.76 to 4.85% for profile P3, P4 and P5.While the content of Fe o is lower than the Al o with variation from 4.68 to 9.43% for profile P1, P2 and P3, and from 0.43 to 0.87% for profile P4 and P5.The content of (Al o + 0.5 Fe o ) varied from 7.4 to 57.8% for profile   5).
It should be noted although the pH NaF is not to be one of the requirements for andic soil properties; it can be used as indicator for soils that contain of amorphous materials.Data on Table 3 shows that pH NaF of all the profiles are high (pH NaF 11.2-11.9)indicating that the soils contain high amorphous materials.There were clearly observed that the volcanic ash materials had more silica content than the soils derived from volcanic tuff.cmol (+) kg -1 cmol (+) kg -1 Based on the above requirements for andic soil properties, it is concluded that all the profiles are fulfill the requirements for andic soil properties of the second group.Thus the soils can be classified as Andisols order with subgroup of Thaptic Hapludands (profile P1 and P2), Typic Hapludands (profile P4), and Dystric Haplustands (profile P3 and P5).

Mineral Composition of the Sand and Clay Fraction
The composition of light minerals of sand fraction for all the profiles is dominated by high hypersthene and augite (pyroxene), green hornblende, and andesine (intermediary plagioclase), and volcanic glass, and rock fragments, with few weathered mineral fragments (Table 6).The composition of heavy minerals of sand fraction is also similar as light minerals, which is dominated by hypersthene, augite and green hornblende.The content of opaque and quartz as resistant minerals are low for all the profiles.This indicates that the weathering process in initial stage.The present of high hypersthene, augite and andesine indicates that the parent materials are classified as intermediary or andesitic volcanic character of the eruption products.This is in   (1990).The amount of weatherable mineral reserve, including volcanic glasses, is very high (48-81%).Therefore the soil nutrient reserve is considered high, and in long terms it is expected to supply the nutrient need from the weathered minerals for crop growth.

Land Management Implication for Agricultural U s e
The volcanic soils that were developed in the Flores Island, indicated the conditions influence the characteristics of the soils.At the first places, the parent material of the soils from the volcanic ash, have more fertile with higher cation exchange capacity, and bases.The clay mineralogical of soils derived from volcanic ash tended having more kaolinitic clays than the soils derived from volcanic tuff (Mt.Ambolumbo, Mt.Kelimutu, and Mt.Egon).
The volcanic soils of the island are considered to have good characteristics.It is reflected by thick solum, medium soil texture with friable consistency, P1: Mt.Mandasawu, Ruteng (1,500 m asl.)P2: Mt.Wawolika, Bajawa (1,300 m asl.)P3: Mt.Ambolumbo, Boawae (1,100 m asl.)P4: Mt.Kelimutu, Ende (1,400 m asl.)P5: Mt.Egon, Maumere (750 m asl.) cm fertile, and easy to tillage and root crop growth.The organic materials are high especially in top soils, soil pH is slightly acid to acid, and moderate to low content bases, which are to be favorable condition for nutrient availability to crop growth.Beside that, the amount of weather-able mineral reserve is considered very high which could support to nutrient supply for long terms.The climatic conditions were clearly shown in their amount of weathered minerals.The western part of the island has more rain.
The main problem of the volcanic soils for agricultural use is slope steepness.It has potential to erosion and landslide, especially for the soils planted with annual crops if it is often to tillage periodically, and the sur face soils becomes open without vegetation.To solve the problem, it is recommended to apply soil conservation technique properly, such as terracing, raised bed terrace, and contour planting.Suganda et al. (1999) mentioned that contour planting was the best method for controlling runoff and soil loss in highland vegetable cultivation.The other problem is the high P retention, which can reduce the availability of soil P to crops, so that it is need a higher dosage of P fertilizer.Increasing organic materials is very suggested to maintenance high status of soil organic materials such as using crop residue after harvesting.

CONCLUSIONS
The soils developed from volcanic ash parent materials in Flores Island showed different properties compared to the soils derived from volcanic tuff, even though they were developed from the same intermediary volcanic materials.The silica contents, clay mineralogy and sand fractions, were shown as the differences.The different in climatic conditions developed similar properties such as deep solum, dark color, medium texture, and very friable soil consistency.The soils have high organic materials, slightly acid to acid, low to medium CEC.The soils in western region have higher clay content and showing more developed than of the eastern region.All the profiles meet the requirements for andic soil properties, and classified as Andisols order.
The mineral composition of sand fraction was dominated by andesine-hornblende-augitehypersthene association, except soil profile from Mt. Kelimutu was dominated by volcanic glassesandesine-augite-hypersthene association.The mineral composition of clay fraction was dominated by disordered kaolinite and disordered halloysite.The high mineral reserve could supply the nutrient need for crop growth for long terms.
The volcanic soils have good soil characteristics which can support increasing agricultural production both annual and perennial crops.The land management for the land should be focused on the increasing organic materials and P nutrient, and soil conservation to control soil erosion and land slide.

Figure 1 .
Figure 1.Location of soil profiles in Flores Island.

Table 2 )
showed an increasing amount of rainfall from east to west area of the island; with average annual rainfall vary from 1,206 mm in Maumere, to 3,070 mm in Ruteng.Rain season is occurring in November to March.The average temperature varies between 26.6-29.3o C in Maumere, and 18.5-20.8o C in Ruteng.Flores Island belongs to Afa climate type in western part with B rainfall type, and Awa type in eastern part with D rainfall type

Table 1 .
Location, slope, parent material, land use and elevation of the profiles studied.

Table 2 .
Average monthly rainfall in the Flores Island.

Table 4 .
Chemical properties of the profile studied.

Table 5 .
Andic soil properties of the profile studied.

Table 6 .
Mineral composition of sand fraction of the profile studied.

Table 7 .
Mineral composition of clay fraction of the profile studied.