Properties and reclassification of volcanic soil in Sungai Kamuyang village, West Sumatra

This study was aimed to examine the classification of soil in Sungai Kamuyang, West Sumatra by the USDA Soil Taxonomy up to the level of familty. This research was conducted in Sungai Kamuyang, Luak District, Limapuluh Kota Regency, West Sumatra, Laboratory of Soil Science Andalas University, and Laboratory of Soil Chemistry and Soil Mineralogy of Soil Research Center, Bogor. This research used a survey method with several stages: Preparation, Pre-Survey, Main Survey, Soil Analysis, and Data Processing. Based on the resluts in classification of Soil in Sungai Kamuyang, it found differences in the resluts in classification of Soil in Sungai Kamuyang served Land Unit Map Solok Sheet by Soil and Agroclimate Research Center in 1990, which is only on the profile SL3 showing characteristics of Andisols while on the other profiles show Inceptisols characteristics.


Introduction
Nagari Sungai Kamuyang, West Sumatra is located in the north of Mount Sago so that this area was classified as stratovolkan physiography. The area is located at an altitude of 506 -2.225 meters above sea lecel. The geology in this region based on the Solok Sheet Geological Map number 0815 has two types of parent material. Qamg parent material is the product of Mount Malintang Andesite rocks, Qpt2 is the result of Tuff pumice and andesite basalt. This parent material will give a big influence on the soil properties.
Based on the Land Unit Map Solok Sheet number 1085 scale of 1 : 250.000 by Soil and Agroclimate Research Center in 1990, the soil type in Nagari Sungai Kamuyang was classified into greatfroup Hydrandepts and Dystrandepts. Based on the Soil Classification System in 1975, Dystrandepts and Hydrandepts in the 7 th Approxination Classifisication Systems are a greatgroup of Andept as a subordo of Inceptisols. By Smith, this Andept Subordo was used in the Classification of Soil Taxonomy A Basic System of Soil Classification for Making and Interpreting Soil Surveys in 1978 and officially used in the Soil Taxonomy in 1990 and now as a new Ordo, namely Andisols.
Andisols are soils formed from volcanic ash, pumice, and/or other volcanic eruptions, which have ≥60% of Andic soil charactersitics to a depth of 60 cm. This soil has an exchange complex dominated by amorphous compound of Al, Si, and/or Fe, and humus. This soil was composed of sand fraction's minerals in the form of quartz, plagioclase, hornblende augite, hypersteine, olivine, and volcanic glass. The clay minerals are dominated by non-crystalline clay minerals consistine of allophane, imogolite, and/or ferritic acid in addition to halloysite, gibsite, and cristobalite, has bulk density ≤ 0,90 g/cm 3 , phosphate retention ≥85%. Epipedon identified of this soil, among others melanic, umbric, or ochric and have cambic horizon on the bottom layer [1,2].
However, there is no specific characteristics of Andisols on the soil layer to a depth of 60 cm [3]. In addition, from the results of soil properties analysis, which found the available phosphorus content was very high with a value of 39 ppm. This is inversely proportional to the statement of [4] that

Material
The main tools used in this study are maps, climate data research (rainfall, temperature, and soil temperature), GPS, Abney level, drill of soil mineral, ring samples, Munsell Soil Colour Charts, knive, soil profile description cards, stationery, and laboratory equipment. The materials used are labels, rubber bands, plastic bags, and chemicals needed for soil analysis in the laboratory.

Methods
The research was conducted in Sungai Kamuyang Village, Luak District, Limapuluh Kota Regency, West Sumatra. The soil analysis conducted in Soil Science Laboratory of Andalas University and Soil Chemistry and Mineralogy Laboratory of Soil Research Center, Bogor. The method used in this study is a semi-detailed survei method with a map scale of 1 : 50.000. Sampling was done by Purpossive Random Sampling based on land units with an area of more than 25 hectares. The satges of this reasearch consisted of: preparation, pre-survey, main survey, laboratory analysis, and data processing. Data obtained in the field and in the laboratory are used as a basis for determining soil classification according to the USDA Soil Taxonomy System by [7] from Ordo to Family level. Observation of soil characteristics in the field is done through observing the soil profile. Soil profile is done on each land units with a size of 1,5 m (length) x 1.5 m (width) x 1.5 m (height). Soil sampling is done in two ways, namely satellite soil sampling and undisturbed soil sampling. Satellite soil samples are taken from each horizon A and B in the soil profile. Undisturbed soil samples is carried out using the ring samples on horizon A and B. The physichal characteristics of land observed in this study are slope, erosion, drainage, and surface rocks. Soil properties analyzed in this study were soil texture, base saturation, pH (H 2 O, KCl, and NaF), C-Organic and organic matter, base cations (Ca, Mg, K, and Na), melanic index, and Al, Fe, and Si Oxalate extract.

Climate Research Area
Based on the Schmidth Fergusson Climate Classification Systems, during the 10 year observation period, Nagari Sungai Kamuyang was classified as type B climate (wet; 14,3% < Q < 33,3%) with a Q value of 24,8%. The pattern of rainfall from the average rainfall for 10 years (observation period 2008 -2017) shows that in Nagari Sungai Kamuyang have two peaks of rainfall in April with an average rainfall of 242,6 mm/month and November with an average rainfall of 350,7 mm/month. There were no dry month because the lowest rainfall was 91,6 mm. The humid month occur in June and July with rainfall ranging between 91,6 to 92,9 mm/month. The wet month occur in January, February, March, April, May, August, September, October, November, and December with rainfall ranging from 131,2 to 350,7 mm.month. Soil moisture regime can be determined by looking at the pattern of the rainfall in the research area. Based on existing rainfall data, note that the rainfall in research area is distributed troughout the year so that the soil does not dry for 90 days cumulative throughout the year. Based on this, the soil moisture regime at the research area is Udic.
Temperatures in Nagari Sungai Kamuyang are in the range of values from 12,95 o C to 23,26 o C. The soil temperature at the research area was obtained from the formula of [8] by adding an air temperature of 2,5 o C. It is based on research [9] which is the average in the United States by an additional 1 o C to 2 o C temperature of the soil and elsewhere. Whereas in the tropics there was an increase in the soil temperature of 2,5 o C from the air temperature, so that the soil temperature obtained at the research area was 22,6 -25,57 o C. From the soil temperature value, the soil temperature regime at the research area is isohypertermic with a soil temperature > 22 o C with an average temperature difference in the summer and winter less than 6 o C. The difference in soil temperature less than 6 o C is supported by the statement of [10] that changes in soil surface temperature in Indonesia in the period 1979 -2009 in the rainy and dry season ranged from 0,5 to 1,5 o C. In addition, [11] stated that changes in the soil surface temperature in West Sumatra during the period 2007 -2013 were recorded at a maximum of 4 o C.

Soil Morphology Characteristics
Of the seven soil profiles observed, each has a different morphology. In 5 th profile, it was found horizons that were already dominated by rocks called C or B/C horizons at a depth of 30 cm. However, on 1 st , 2 nd , 3 rd , 4 th , 6 th , and 7 th profiles, horizon B was found in deeper solum with an average depth more than 100 cm.
The soil color on each profile tends to be darker (brown to black) with Hue 7,5 YR and 10 YR on 1 st , 2 nd , 3 rd , 4 th , and 7 th profiles with varying values and chroma of 2/2 to 5/6, while the 5 th and 6 th soil profiles has a color with a 7,5 Y Hue with a value of values and chroma 2/2 to 6/1. The color of the soil will affect other soil properties through radiation from sunlight energy. The heat energy contained in the darker soil will result in higher evaporation rates so that the darker soil will dry out faster than lighter colored soils [12]. The color of the soil can indicate organic matter in the soil because organic matter gives a dark or blackish color. According to [13], the higher content of soil organic matter the darker color of the soil. In addition, the color of the soil can be used to determine the level of weathering. The reddish soil color indicates the level of weathering is getting further.
Soil structure was also observed in observing soil profiles. The soil structure in each soil is dominated by granular structure and angular with a moderate level of development. Soil structure affects the movement of water in the soil. Crumb structure will have more porous space than angular structure so that water will enter the soil more quickly [14].

Soil Physical Characteristics 3.3.1 Bulk Density
Based on the results, that the average of the soil bulk density is < 1 g/cm 3 is equal to 0,59 to 0,88 g/cm 3 . The low bulk density can be caused due to an amorphous mineral content in the soil so that number of micropores is quite a lot, especially intra and inter particle pore space. Higher bulk density will affect the pore spaces of the soil, the lower bulk density will be higher pore space [15]. Low soil bulk density due to allophane contributes to the development of pores in the soil structure. The pore arrangement of allophane structure unit causes allophane porosity to be high [16]. [17] stated that allophane has a perforated structure and with a diameter of 3 -4 mm. The heavy of soil bulk density will be lower along with the increase in allophane content because of 25 -45% of the pore volume of Andisol is occupied by allophane.

Soil Texture
All soil profiles have a very high clay fraction with a range of 18,72 -81,6 %, with the highest clay fractions found in the 7 th profile and the lowest clay fraction found in the 1 st profile. The high clay fraction in each profile shows that the soil has undergone further weathering. Most of the soil has more clay content in horizon B compared to horizon A. The older the soil, the difference in clay content between horizon A and B will be even greater. The content of each fraction (sand, silt, and clay) in each soil horizon is influenced by three things, the movement of clay from horizon A to horizon B dueto percolation water, chemical weathering from clay in horizon A and leaching dueto drainage water, and weathering silt and sand so as to form clay on the horizon B [18].

Soil Chemical Characteristics 3.4.1 Soil Reaction (pH)
Based on the results, pH values ranged from 4,56 to 6,75. The diversity of soil pH values is caused by weathering that occurs. In the weathering process, when base cations (Ca, Mg, K, and Na) are detached from spcace between the micelles then the pH will increase, whereas if the loose cations of Al, Fe, and Si then the pH will tend to decrease [19]. In soils with moderate acidity, aluminium and hydrogen compunds cause hydrogen ions to dissolve in the soil. Al-hydroxide ions adsorbed and transformed into exchangable cations. In the soil solution, Al-hydroxide will produce H ions due to Al hydrolysis reaction [20]. The pH delta values obtained to negative value, this indicates that many colloidal soils have negative charges so that it has ability to bind positively charged base cations [19].
The pH values will determine the amount of positive and negative charges on the surface of the colloid. If the delta pH value of ± 0,5 indicates that the soil is variable, that is the charge changes according to the increase and decrease of soil pH [21]. Increase and decrease of soil pH is influenced by the input given to the soil, either in the form of inorganic and organic fertilizers or various types of ameliorant material such as phosphate rock or volcanic ash. The value of NaF pH obtained in each soil ranged from 8,7 to 11,49. The high pH of NaF in this soil indicates that the soil is contains high amorphous material which dominates the exchange complex. This is based on the ligand exchange between F-and OH-which is on the edge of allophane so that OH-is free and will quickly replace the pH of solution [22].

Soil Organic Matter
C-organic content in each soil ranges from 2,72 to 3,15% with moderate to high criteria. The content of soil organic matter in the soil ranges from 4,67 to 5,41%. According to [23], the high content of organic matter in the soil may be due to the presence of amorphous clay. Organic matter will produce humus that will bind to the Al and Fe into the Al-humus and Fe-humus or would happen polycondensation with amorphous minerals. Amorphous mineral compounds stabilized organic matter and protect them against biodegradation of microorganisms and stimulate the accumulation of organic compounds in the soil. These compound will be stable and remain in the soil and will not have movement [24]. In addition, high clay content in the soil also effects the content of organic matter in the soil. Clay fraction has an influence on soil organic matter because the largest specific surface area is 800 m 2 /g. The large surface area has a high activity in water adsoprtion, so that the soil which is dominated by clay fraction will have a high water holding capacity with low pore aerase. The low pore aerase causes a semi-anaerobic state so that the air exchange is not smooth. This affects the decomposition of organic matter that will undergo humification process to produce organic compounds that are resistant to weathering [25,26].

Base Cations and Base Saturation
Based on the results, the value of base cations in the soil varies from very low to high, base saturation is very low to high with a value of 16,8 -70,98%. Ca 2+ content in the soil ranges from 1,96 -4,51 me/100g of soil (very low to high), Mg 2+ content in the soil ranges from 1,25 -1,95 me/100 g of soil (moderate), K + content ranges from 0,59 -0,92 me/100 g of soil (high), and Na + content ranges from 0,46 -0,9 me/100 g of soil (high). The low Ca and Mg values in the soil caused by leaching due to high rainfall. Ca and Mg cations are the most occupying the surface of colloids, so that when rainfall was high, leaching will occur and base cations will be lost [27]. Bases that can be exchanged have a relationship with base saturation, cation exchange capacity, and pH. If the soil pH is high, the base saturation will tend to be high because many base cations are absorbed in the soil colloid, conversely if the pH is low, the base saturation will tend to be low because the cation absorbed in the ground colloid is dominated by Al and Feions [28].

Phosphate Retention and Al, Fe, Si, Oxalate Extract Content
The phosphate retention in each soil show values ranging from 35,5 to 97,5%. The high phosphate retention in soil is due to the amorphous iron and aluminium content derived from aluminium hydroxides and allophane. Al-OH and Al-OH 2 functional groups contained in amorphous mineral are very important in absorbing phosphate ions. Aluminol group is a hydroxyl anion which has a single bond to the aluminium metal. This single bond causes OH to be easily exchanged by phosphate ions through the ligand exchange mechanism. The more aluminol groups in amorphous materials such as allophane, the more phosphate is absorbed in the soil [29]. According to [4] , a high phosphate retention resulted in phosphate becomes insoluble and unavailable to plants. Phosphate retention in one of the requirements of andic soil properties if phosphate retention more than 85%. [30] states that high phosphate retention in soils is directly proportional to allophane present in volcanic soil and the P-bond by allophane cannot be released by the help of organic matter. The metal content of Fe oxalate extract (0,41 -9,2%) was higher compared to Al (0,26 -2,38%) and Si (0,14 -0,52%) for all soil profiles. The content of Si is lower than Al and Fe because Si ions are more mobile and easier to leaching than Al and Fe so Si leached in the top soil will be lossed and accumulated in the sub soil, whereas Al and Fe more easily make humus complex [31]. This is supported by the agreement of [32] that materials which are rich in weathered minerals such as volcanics substnaces which produce top layers containing high Al and Fe. This situation increases the composition of complexes with relativiely high metals to that only slighlty soluble in air. Soils that have Andic soil properties must meet the requirements set forth in Soil Taxonomy. One of the requirements that must be met is the value of Al o + ½ Fe o contents ≥ 2%. The value of Al o + ½ Fe o eligible andic soil is on 3rd, 4th, and 6th soil profiles with values ranging from 2,145 to 5,01%. The high content of Al, Fe, and Si Oxalate extract in these three soils indicates the presence of amorphous material. Amorphous clay minerals such as allophane, imogolith, Al/Fe-Oxide, Al/Fe-hydroxides, and ferrihydrite has a main constituent mineral soil colloids [16].

Melanic Index
The deeper the depth of the soil, the value of the melanic index also decreases. This is duet o the low fulvic and humic substances as indicators of the melanic index [33]. Melanic index is used for the melanic epipedon characteristics requirements which the melanic indeks value must be ≤ 1,7 in cumulative soil thickness of 30 cm. In this research, there was no soil profiles that qualified as a melanic epipedon. This index is associated with the rasio of humic and fulvic acids in the organic fraction of the soil [34 ] . The melanic index is used to differentiate accumulate organic matter which is though to be produced from large amounts of graminae vegetation from humidified organic matter formed from forest vegetation. Melanic index is calculated as the absorbance of the extract solution at a wavelength of 450 nm divided by the absorbance at a wavelength of 520 nm [7].

Soil Classification
In this research, soil parent material derived from pumice tuff formation and rocks andesite Mount Malintang and produce volcanic soil with Andic soil properties. Based on [7], Andic soil is a soil that has a bulk density ≤ 0,90 g/cm 3 , phosphate retention ≥ 85%, and Al o + ½ Fe o content ≥ 2%. From the results, it is obtained in 3 rd soil profiles meets the characeristics of the Andic soil. In classifying the soil, it is necessary to determine the identifier epipedon and horizon based on data obtained from observing and analyzing soil properties in the laboratory. Based on the data, all soil profiles meet the requirements of umbic epipedon which the soil has a thickness of more than 18 cm, the soil structure is sufficiently developed and soft if it dry has colors with values and chroma ≤ 3 (wet) and ≥ 5 (dry), base saturation (NH4OAc) ≤ 50%, and average C-organic content ≥ 0,6% and moist for 90 cumulative days throughout the year. After identifying the epipedon, it is followed by identification identifier diagnostic horizon, which both soils meet the requirements as a cambic horizon. Soil has a subsurface horizon thickness of ≥ 15 cm, with a fine soil texture and not hard soil, soil color does not change when opened in the air, and genetic soil development without extreme clay accumulation. After determining the identifier epipedon and horizon on the soil profiles, it is followed by determining soil ordo based on the Soil Taxonomy by [7]. The 1 st , 2 nd , 4 th , 5 th , 6 th , and 7 th soil profiles when viewed from morphology, identifier epipedon as well as subsurface horizons belong to the Ordo Inceptisols. According to [35], Inceptisols are soils with a cambic horizon with the upper limit at a depth 10 cm from the surface and its lower limit at a depth of more than 25 cm. The 3 rd soil profile meet the requirements of the andic soils so that belong to Ordo Andisols. Andisols are soils that have 60% of the thickness of the andic soil properties with 36 cm thick or more at depths of less than 60 cm [7].
Soil classification at the Sub Ordo level was determined based on the soil moisture regime, which in the research site has a Udic regime so that the Sub Ordo at 1 st , 2 nd , 4 th , 5 th , 6 th , and 7 th soil profiles are Udepts and the 3 rd soil profiles is Udands. The Greatgroups category in 1 st , 2 nd , 4 th , 5 th , 6 th , and 7 th soil profiles is Dystrudepts because the soil has a base saturation (NH4OAc) less than 60% and 3 rd soil profile is Hapludands because the soil properties does not qualify for the other greatgroups. At the Sub Group level, the 1 st , 2 nd , 4 th , 5 th , 6 th , and 7 th soil profiles were classified into Andic Dystrudepts because all horizons has a thickness more than 16 cm with fine soil fractions with bulk density less than 1 g/cm3 and have a total Al o and ½ Fe o percentage more than 1%. The 3 rd soil profile was classified as Typic Hapludands because the soil properties does not meet requirements of other subgroups.
At the Family level, soil classification based on three types were grain structure, mineralogy class, and soil temperature regime. In the 1 st , 2 nd , 4 th , 5 th , 6 th , and 7 th soil profiles have fine silt grain size (having less than 15% weight of particles with 0,1 -7,5 mm in diameter, fine soil fractions having clay content of 18 -35%). In the 3 rd soil profile, it has a medial grain size because it only has fractonal of stones less than 35%. The mineral classes in 3 rd soil profile belong to the Amorphic class with values of 8 × Si o + 2 × Fe o > 5% and 8 × Si o > 2 × Fe o . The parent material derived from volcanic material and high rainfall causes the formatio of amorphic clay minerals at a further development will be followed by the kaolinite mineral. This can indicate that the mineral class in the 1 st , 2 nd , 4 th , 5 th , 6 th ,