Research On Soil Genetic Characteristics And Taxonomic Classification Of Typical Soil Types In The Xi-Shui Forest Zone Of The Qilian Mountains

The study according to the genetic characteristics and classification of soil is the premiseof identifying soil properties and investigating, evaluating and drawing with soil resources.Quantitative soil taxonomy is the future trends of soil classification. Study of the Chinese soiltaxonomy began in1980s, after nearly30years development, this system has been improved,with its application scope gradually been widened. As the main one in the Northwest China,Qilian mountains play a great role can not be replaced in keeping the development ofeconomy in Hexi area and maintaining the ecological balance of the whole northwest China.The study according to the soil characteristics of Qilian mountain has less systematicness fora long times, and the classification on it especially the taxonomy also relatively less.This study was conducted to determine the genetic characteristics and taxa of four soiltypes in the Xi-Shui Forest Zone of the Mid-north in Qilian Mountains. The soil types werebrown calcic soil, grey cinnamon soil, chestnut soil, and alpine meadow soil. Four typicalsample was setted based on the four soil types, factors of soil formation and characteristics ofprofile were investigated. Three to five genetic horizons were divided and then sampled. Thetaxa included order, suborder, group and subgroup of four soil types were retrievalled underthe Keys to Chinese Soil Taxionomy（3rd edition）. The results indicated that:1. The depth of soil in the forest zone was shallow, but profile of chestnut soil wasprofound. Soil parent material include residual, alluvial and diluvial parent material primarily.The content of chad（≥2mm）in chorizon is high and have coarse texture. The brown calcicsoil have the most obvious coarse texture, its bulk density is small and ventilation porositywas more bigger.2. There have a certain thickness dead leaves and branches on the surface of soil in theforest zone, and organic matter accumulated obviously. With the effect of this process, thecorlor of the overall soil profile was brown（YR）, and being dark in the up location. Soil structure was changed from granular to nuclear and massive. The water conservation of soilwas high（Saturated water content changed from30.67to81.85%, capillary water contentranged from26.78⁶2.79%）. Organic carbon, total nitrogen, available phosphorus andphosphorus, rapidly-available potassium content, Cation exchange capacity activated Fe₂O₃,complexation Fe₂O₃, activation grade and complexation degrees decreased as soil depthincreased. The content of exchangeanle base was higher in the upper location. The strength oforganic matter accumulation was different between four soil types, The alpine meadow soilhad the highest accumulation followed by the grey cinnamon soil, the chestnut soil, and thenthe brown calcic soil.3. The annual precipitation of four area with four soil types changed from303.52to523.56mm, have the typical characteristics of arid mountainous regions, and intensity of soilleaching is relatively weak. With the role of low leaching, the content of exchangeable base inleaching and illuvial horizon was higher than that in chorizon. Moreover, the vast majoritybelongs to the base saturation （>50%）, freeing with exchangeable H+of Al3+. With high pHvalues（＞7.50）, the soils are alkaline, pH values and base saturation percentage decreasing asthe deeper of the profile. The difference of the clay content (between107.81-273.75g kg^-1)of various levels is small and the carbonate content ranged from15.86¹91.11g kg^-1.Thegroundwater level of forest areas is low, and the profile still has a certain water-soluble salt(between0.37¹.85g· kg^-1), profile higher washing loss, between17.17¹93.93g kg^-1. Theorder of the forest soil eluviation is alpine meadow soil> grey cinnamon soil≈chestnut soil>brown calcic soil.4. The physical weathering and chemical weathering of the forest region of four soiltypes is relatively weak. Compared with the South strongly weathered soil type, soil claycontent (107.81-273.75gkg^-1) is lower, and the ratio of the powder and clay particle（0.72-3.27） is larger while the free iron oxide content and degree of freedom (7.82¹7.50g kg^-1,20.55³6.99%) is lower. However, the aluminosilicate rate （4.13-6.29）, the ferrosiliconrate （31.13-40.35） and the Si-Al-Fe ratio （3.67-5.38） is higher than the other indexes. Inconclusion, the differences of the degree of weathering between the different soil types is notmarked.5. Four soil types of forest area have two diagnostic surfaces, including the mollicepipedon and aridic epipedon. They have three diagnostic subsurface, including argic horizon,calcic horizon and calcipan. In addition, they have four types of diagnostic characteristics,including soil moisture conditions （aridic, ustic and udic）, soil temperature conditions （frigid and gelic）, isohumic property and base saturation.6. According to the retrieval, four types of forest soils belongs to three soil orders, threesuborders, four soil groups sand four subgroups. Profile0407and0408are both included byBoric Luvisols of Luvisols. Profile0407belongs to Cal-Mol-Boric Luvisols of Mol-BoricLuvisols while Profile0408belongs to Typ-Hap-Boric Luvisols of Hap-Boric Luvisols.Profile0409belongs to Udic Isohumisols of Isohumisols and Typ-Hap-Udic Isohumisols ofHap-Udic Isohumisols. Profile0410belongs to Orthic Aridisols of Aridisols andPan-Cal-Orthic Aridisols of Cal-Orthic Aridisols. In the retrieval results, only profile0410ofthe4types of forest profiles accords with the ratio of the genetic classification typical profile.7. In this study, referring to the existing achievements, it is necessary to study the soilcharacteristics and classification system of the other types of soil, make clear the verticaldifferentiation boundaries under the category of the classification of soil and discuss thegrassroots classification work in even more areas. In the current application process ofChinese soil taxonomy, some determination methods of the operability and accuracy still hassome shortages, and this limits the continuous development of Soil Taxonomy. With theadvances in basic science, Methods of the determination are are also constantly improving.The improvement and standardization of the methods will be more conducive to the furtherdevelopment of Soil Taxonomy.