Scientific registration n : 1372 Symposium n : 7 Presentation : poster Humus State as an Essence of Soil Formation in Highmountain Soil of Central Caucasus Etats de l humus, comme élément essentiel de la formation des sols de haute montagne dans le Caucase central KIRVALIDZE David ( 1 ), KIRVALIDZE Revaz ( 2 ), JACOBASHVILI Izolda ( 3 ) (1) Soil Science Department, Georgian Agrarian University, Tbilisi 380031 GEORGIA (2) Soil Science Department, Georgian Agrarian University, Tbilisi 380031 GEORGIA (3) Department of agrochemistry, Georgian Agrarian University, Tbilisi 380031 GEORGIA 1. Introduction High-mountain zone is the considerable part of Georgian territory. The soil cover of this zone, consists mostly of mountain-meadow soils, characteristic of about 20% of country s territory. It has quite important role in agriculture, as the natural pasture grounds. For today these soils are not studied enough, especially the main component humus, which has quite important role in high-mountain soils because of its high content. At the same time diverse ecological conditions in high-mountain zone reflect in humus creation process and special humus state is formed, studying of which bears quite important theoretic essence along with its practical role. Central Caucasus, located between the peaks Ialbuzi and Mkinvartsveri (Kazbegi), is the highest and geomorphologically most complicated part of the Greater Caucasus (Javakhishvili, 1947; Geomorphology of Georgia, 1971). The whole territory of studied region, which are from 1800-1900m to 2500-2600m above sea level, is the moderately humid climatic zone with considerably dry, cold winter and short summer ( Kordzakhia, 1961). Subalpine and alpine plant communities are developed. Soil cover is presented by mountain-meadow soil type consisting of following subtypes: mountain-meadow sod, mountain-meadow peat, mountain peat, secondary mountain-meadow and mountainmeadow sod with second humus horizon. 2. Methods Aim of research involved investigation of high-mountain soils of Central Caucasus, and peculiarities of their humus state. 1
Mountain-meadow sod, secondary mountain-meadow, mountain-meadow sod with second humus horizon and mountain peat soils have been studied and their organic matters were investigated by the following properties : total humus content and carbon %, humus group and fractional composition, optical properties of humus acids, content of lipids, chlorophyll and Pg-fraction, reflection capacity of soil in accordance with total humus amount and its composition, etc., alongside with other basic soil parameters. According to obtained results the humus state of high-mountain soils of Central Caucasus has been established (see table 1). 3. Results Very high content of humus in upper horizon (19-20%) of mountain-meadow sod soils and drastic of humus in its profile directly indicates peculiarities, characteristic to processes of humus formation and soil formation: tussock plants growing on these soils despite short vegetative period, typical for this region, produce abundant biomass, the main part of which is concentrated in roots. At the same time the root system is located mostly in a top layer of profile, causing sod formation. Above-ground and underground parts of these plants yearly, after falling temperature dye and regeneration buds stay only in root collar, from which a new plant grows up next year. Transformation of accumulated organic matters is hindered due to short biologically active period. Micromorphological research of these horizons shows that slightly humificated organic remainders are accumulated in large amounts. Microscope evidently shows plant remainders, having differently kept anatomical structures. Large amount of humus provides high absolute content of nitrogen, but taking into account the C/N ratio we shall see that despite such high absolute content, degree of humus richness by nitrogen is relatively low (see table 1), showing also the hindrance of humification process. Fulvic acids abundance in humus composition - fulvatic nature of humus, existence of pigment chlorophyll and high content of non-specific humus substances in humus show low intensity of humification process. It is known (Kumada, Hurst, 1967; Kumada et al, 1967; Kononova, 1968; Aleksandrova, 1989; Orlov, 1990), that acid reaction and high development of fungous microflora causes abundance of fulvic acids. Existence of fungous microflora is proved by presence of Pg-fraction, which is the product of the fungus Cenoccocum graniforme ( Kumada, Hurst, 1967; Orlov, 1990 ). At the same time presence of Pg-fraction shows, that these soils are under over-humidity and preference of anaerobic processes over aerobic often takes place. This is the reason of the prevalence of the first fraction of humic acids over the second fraction. Besides, it is known that the process of chemical weathering is hindered in highmountains and mainly the physical weathering is going on, causing formation of skeletal soils. 2
Reduction of chemical weathering results in low release of different elements from parent rock, among them calcium and magnesium, causing base non-saturation of these soils. The low composition of calcium ion in soil is one more reason of shortage of second fraction of humic acids. fulvatic fulvatic fulvatic fulvatic Table 1 Humus State of High-mountain Soils Soil N Indicator Mountainmeadow sod MM with second humus Secondary mountainmeadow Mountain peat horizon 1 2 3 4 5 6 1 Humus content in top horizon % 13,0-20,0 very high 14,0 very high 5,0-6,0 high 27,0 very high 2 Humus distribution through the profile drastic gradual drastic drastic 3 Humus richness by nitrogen C/N 8,0-11,0 medium 8,0-10,1 medium 8,0 medium 17,0 very low 4 Humification degree of medium medium low medium organic matter C HA /C T x 100% 5 Humification degree of low low low very low organic matter after Gorelova C HA x E HA 6 Humus type C HA / E FA 7 Content (%) of free humic high high medium high acids from the total amount of humic acids 8 Content (%) of humic acids very low very low low very low bounded with Ca 2+ from the total amount of humic acids 9 Humin content % from the low low low low total C 10 Optical density of humic acids low low low very low 0, 001%,HA E 465nm, 1cm 11 Content of Pg-fraction + + - + 12 Content of pigment + + + + chlorophyll Optical density of humic acids is quite low (see table 1) and shows that humic acids have well-developed peripheral, aliphatic part and not high degree of benzoidity. This is one more example of hindrance of humification process. It was decided to calculate the degree of humification process for high-mountain soils with following formula - C h x E hm (Gorelova, 1982) because this indicator, calculated only with total percentage of humic acids C hm /C s x 100% can not shows precisely the essence 3
of humification process in high-mountain and sometimes has higher value - irrelevant to these soils. Mountain peat soils, differently from mountain-meadow soils are formed under Rhododendron caucasicum scrub. Surfacing made by Rhododendron caucasicum rough leaves limits penetration of sun rays and oxygen to soil, causing development of anaerobic processes. Analogically a lot of organic substances are accumulated here, which are slightly humificated and humus has abundance of fulvic acids. Existence of green pigment shows development of fungous microflora, which is also the one main factor of abundance of fulvic acids. Nitrogen composition in humus is also low. Humic acids have simple structure and according to extinction coefficient ( E ) and infrared spectral analysis, is similar to fulvic acids. As to humification degree, according to Gorelova this indicator is quite low and fully corresponds to real picture of the humification process of these soils. The pigment chlorophyll and big amount of nonspecific humus compounds were founded as well. Humus state of secondary mountain-meadow soils shows many such qualities, which are common to high-mountain soils, but here exists the fact that previously these soils were covered with forest and the process of humus formation was going by another way. Usually in forest soils humus is accumulated in upper horizon and under and under drastically decreases (Ponomariova, Plotnikova, 1980; Orlov, 1990), because the considerable part of organic remainders are the fallen plants on soil surface. The analogue picture have other high-mountain soils - humus distribution in profile here bears also drastic character and the difference makes the fact that the absolute amount of humus substances are not similar. The total amount of humus in upper horizon of secondary mountain-meadow soils is considerably lower, amounted to 5-6% than in other high-mountain soils (>10%). This has some reasons: at first the sod formation process in secondary mountain-meadow soils is weaker and accumulation of organic remainders is going with less rate than in other soils; Erosion processes on these soils are going quite actively because of less development of sod formation and humus is not accumulated with high amount. At the same time the mentioned secondary mountain-meadow soils are studied at slopes and that s why over-humidity processes are not frequent and anaerobic processes are also slightly developed. This is proved by low composition of Pg-fraction. The fungous microflora is not well-developed because of not so acid actual reaction, as in other studied high-mountain soils. The temperature which is slightly higher also makes influence. Abundance of second fraction of fulvic acids in humus shows connection between this soil and the forest in the past. In total, humification process is hindered here also. Humification degree is low, humus is fulvatic, and there are mostly mobile forms. Humic acids have simple structure - slightly developed aromatic, and powerful aliphatic structures - showing its resemblance with fulvic acids. E - quantity is low. Non-specific humus substances, among them the pigment chlorophyll were also recorded. 4
4. Conclusions Summarizing results can be concluded, that humus state of high-mountain soils of Central Caucasus is formed under specific factors, peculiarities of which is shown in humus state parameters of soils of this zone. Short biologically active period of soil limits humification process in this region, causing formation of fulvatic humus with abundance of mobile substances and low amount of nitrogen. Main part of nitrogen is in peripheral part of humus acids. Humic acids have simple structure, low degree of benzoidity, welldeveloped aliphatic structures and very low optical density. There are abundance of nonspecific humus substances. Pigment chlorophyll and Pg-fraction, which are the result of acid reaction, high humidity and well-developed fungous microflora, has been recorded. These common qualities of humus of high-mountain soils of Central Caucasus are so universal that seems more important than distinctive features. This shows that humus formation process in different soils of this region is mostly similar and as a result of it, resembled humus state for these soils is formed, reflecting definitely essence of soil forming process in high-mountain. 5. List of symbols Ha - humic acids Fa - fulvic acids E - extinction coefficient MM - mountain-meadow T - total C - carbon N - nitrogen 6. References Aleksandrova, L.N., 1989. Soil organic matter and processes of its transformation. Nauka, Leningrad, 287 pp. (in Russian ). Geomorphology of Georgia. 1971. Metsniereba, Tbilisi, 650 pp. ( in Russian ). Gorelova, T.A., 1982. Peculiarities of organic matter of peat, peat-glay and peat-podzolic-glay soils. Dissertation thesis, Moscow. ( in Russian ). Javakhishvili, A. N., 1947. Geomorphological districts of Georgia. Press of Academy of Sciences of USSR, Moscow, 180 pp. ( in Russian ). Kononova, M. M., 1968. The processes of soil organic matter transformation and its connection with soil fertility. Soil Science 8, Moscow, pp 17-27. ( in Russian ). Kordzakhia, M., 1961. Climate of Georgia. Press of Academy of Sciences of GSSR, Tbilisi, 250 pp. ( in Georgian ). Kumada, K., Hurst, H. M., 1967. Green humic acid and its possible origin as a fungal metabolite. Nature, v. 214, pp. 631-645. 5
Kumada, k., Sato, O., Ohsuma, Y., Ohta, S., 1967. Humus composition of mountain soils in central Japan with special reference to the distribution of P-type humic acids. Soil Sci. Plant Nutr., v.13, N 5, pp 151-153. Maruashvili, L., 1961. Physical geography of Georgia. Tsodna, Tbilisi, 343 pp (in Georgian ). Naidenova, O. A., 1962. On the heterogenity of fulvic acids of sod-podzolic, chernozem and gray desert steppe soils. Reports of Leningrad Agricultural Institute 91-1, Leningrad, pp 16-20. ( in Russian ). Orlov, D. S., 1990. Soil humus acids and the global theory of humification. Moscow State University Press, Moscow, 362 pp ( in Russian ). Ponomariova, V.V., Plotnikova, T.A., 1980. Humus and soil formation. Nauka, Leningrad, 220 pp. ( in Russian ). Key words : Organic matter, Humus State, high-mountains, humus formation, humification, soil formation Mots clés : matière organique, état de l humus, hautes montagnes, formation de l humus, humification, formation du sol 6