Some New Diagnostic Epipedons for Soil Classification in China

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SPRING 1988 Some New Diagnostic Epipedons for Soil Classification in China 29 Xueming Yang, W.R. Effland, and T.E. Fenton l China, an ancient agricultural country, has verified by radio-carbon dating that farming practices began about 6,000 yr ago.

1 SPRING 1988 Some New Diagnostic Epipedons for Soil Classification in China 29 Xueming Yang, W.R. Effland, and T.E. Fenton l China, an ancient agricultural country, has verified by radio-carbon dating that farming practices began about 6,000 yr ago. The development of society and the need for improved agricultural production increased the usefulness of a soil classification system. The earliest soil classification systems appeared in two books, Yugong and Guanzi Diyuanpian, in 2,400 to 2,500 B.P. In Yugong, the soils of China were classified into three categories and nine classes based on soil properties such as color, texture, hydrologic characteristics, and other related soil properties. In addition, classification was related to topography, vegetation, and soil use. This system may possibly be the earliest recorded attempt of soil classification in the world. In Guanzi, the soils were classified in greater detail. Soil classification was based on soil properties related to fertility, such as color, texture, structure, porosity, consistence, organic matter, saline-alkali properties, and other related soil characteristics. This system also used topography, hydrology, vegetation, and other natural conditions as criteria for classification. The Chinese soils were divided into 18 classes that each were further subdivided into five subclasses. Concurrently, Chinese soils and their utility and ameliorations were also described in other parts of that book (such as Diguan situ xiapain). The primary purpose of soil classification in ancient times was to estimate land (soil) productivity and improve production, although the soil classes and nomenclature were different. The ancient Chinese soil classification systems were derived from the experiences of agricultural production. Unfortunately, the valuable experiences of classifying, utilizing, and ameliorating soil were not summarized and arranged systematically during the lengthy feudal society era. Written documentation of the work of classifying and identifying soil is limited. The modern Chinese soil classification effort began in the 1930s. More than 2,000 soil series such as Xuwen, Tuerguan, Nanjing, and others were established after the introduction of the Marbut system and the concept of the great group. A few new great groups (purplish, paddy, and other soils) were proposed at this time. This system, however, was not well developed. After 1949, the Russian geo-genetic concept was introduced into China and the direction of soil classification reflected this school of thought. The development of Chinese soil classification based on the Russian concepts can be divided into three stages. The first stage was to study the Russian concepts of genesis and classification. A classification system was established with the great group being used as the basic unit for mapping. The great groups established during this period included drab, yellow-brown, meadow, brown-taiga, black, Baijiang (planosols), dark loess, grey-brown desert, takyr, lateritic red earth, and others. I Xueming Yang was a visiting scientist appointed as an associate lecturer, Agronomy Department, Iowa State University. He is from Changchun, People's Republic of China where he teaches in the Soil Science and Agrochemistry Department, Jilin Agricultural University. At Iowa State University, Mr. Yang worked with the Soil Morphology and Genesis group and studied the U.S. system of soil classification based on Soil Taxonomy. W.R. Effland is a research associate and T.E. Fenton is professor of agronomy, Agronomy Department, Iowa State University, Ames, IA

2 30 SOIL SURVEY HORIZONS During the second stage, Chinese soil scientists devoted more attention to the better farm land and lower units of classification after the first national soil survey (1958). Additional great groups such as Chao (cultivated meadow soils), Mian (loessial soils), Oasis, and other soils were established in accordance with experiences of farmers. Furthermore, a series of alpine and phospho-calcic soils had also been proposed during the survey in the Tibet plateau and Xisha islands. In the late 1970s, the third phase of development of Chinese soil classification was influenced by the U.S. system Soil Taxonomy (Soil Survey Staff, 1975). The soil order concept began to appear in Chinese soil science literature. The concept of the diagnostic horizon was used for classification of paddy soils. The objective of this paper is to discuss several new diagnostic epipedons recently proposed by the Soil Classification Group of the Nanjing Institute of Soil Science (1985). The unique soil conditions of China may require additional diagnostic horizons not yet incorporated into Soil Taxonomy. It is hoped that the broad backgrounds and experiences of this article's readers will provide useful comments on the proposed diagnostic epipedons. Duidian Epipedon This epipedon is a dark surface layer formed by adding large amounts of manure and/or surface layers of higher organic matter content than the underlying material during long-term cultivation. 1. ~ 50-cm thick. 2. The weighted average for organic matter is ~ May contain artifacts (coal, charcoal, brick, etc.). ORGANIC MATTER (%) DUIDIAN EPIPEDON 40 E 60 2 :r: ~ W CALCIUM CARBONATE (%) Fig. 1. Depth distributions for Duidian epipedon.

SPRING 1988 31 The duidian epipedon occurs in loess parent material and is mainly distributed on the terraces of the Fen and Wer Rivers in the provinces of Shanxi and Shensi of central China.

3 SPRING The duidian epipedon occurs in loess parent material and is mainly distributed on the terraces of the Fen and Wer Rivers in the provinces of Shanxi and Shensi of central China. Regional climatic data show annual precipitation ranging from 450 to 700 mm and mean annual temperatures from 13 to 16 C. Formative processes include the use of large amounts of muck (manure) with continual rising of the cultivated surface resulting in subsequent burial of the original plow layer and soil. Loess textural and chemical composition have a strong effect on the properties of this layer. Improvement of soil physical properties is attributed to a thick solum of uniform texture with very friable consistence and high porosity. Increased nutrient-holding and available-water capacities are related to the uniform mineral composition and additions of organic matter. Calcium carbonate (CaC03) is commonly present in the added material. The carbonate content ranges from 0.2 to > Redistribution of carbonates can produce eluvial-illuvial zones and secondary recharge of leached buried horizons is possible (Fig. 1). Artificial-manure (Mellow) Epipedon This epipedon is a dark surface layer formed by additions of manure such as human waste, organic waste, and other village manure during long periods of vegetable cultivation. 1. ~ 50-cm thick. 2. The weighted average for organic matter is ~ ~ 100 ppm available P 20, within the 0 to 20 cm depth (0.5 M NaHC0 3 extraction). 4. ~5% by volume of earthworm (Lumbricus spp.) holes and casts. 5. May contain artifacts. This layer is formed by additions of matter high in organic wastes. The P criteria may imply the use of man-derived materials. The high organic matter content and significant earthworm activity are related to composition of the amendment. Guanyu Epidepon This epipedon is a surface horizon formed by deposition of suspended particles from irrigation water and subsequent mixing of these particles by cultivation. 1. ~ 50-cm thick. 2. A unique mechanical texture in the whole layer. 3. Organic matter content gradually decreases with depth and is at least 0.5% at the bottom of this layer. 4. May contain artifacts. Soils with guanyu epipedons were classified as a great group (Oasis soils) by the First National Soil Survey. They occur in dry areas, particularly in oases in the provinces of Xinjiang (Sinkiang) and Gansu (Kansu). Oasis soils occupy about 10,000 km 2 in China.

4 32 SOIL SURVEY HORIZONS <0.001mm CLAY (%, o E s 60 :z:: ~ A. ~ CALCIUM CARBONATE (%, Fig. 2. Depth distributions for two Guanyu (Oasis) soils. Irrigation was begun about 2,100 to 2,200 yr ago in South Xinjiang and Hexi Zoulang of Gansu. The majority of oases in North Xinjiang were developed in the 16th and 17th centuries. More oases have been developed in recent times. Soils with these epipedons are on the lower parts of alluvial fans, low terraces, and flat to concave upland plains. Water Quality Suspended sediment contents in continental rivers in China are 0.8 to 7.5 kg/ml. In the Keliya River in Xinjiang the clay and sand content is about 2.5 kg/ml. The average amount of clay and sand brought into the farmland during the growing season is about 5,000 kg/ha. Deposition may exceed 2 mm/yr. The thickness of the guanyu epipedon is generally 50 to 80 em, but in some areas it may be 1- to 2.5-m thick. The color, texture, and structure are uniform within a given epipedon but vary in different locations. The recently deposited clay and sand are rich in plant nutrients. There is both a marked eluviation of salt and clay and a biological accumulation of organic matter. In Fig. 2, the depth distributions of CaC01 and clay were influenced by the properties of the deposited material and the buried soil. Pore-crust Epipedon This epipedon is a surface horizon diagnostic for desert soils.

5 ~'It~~,,*OIlS IiEq'ON Cttl.t(HtAt Tung" I. TAIWAN Fig. 3. Distribution of soils with three kinds of epipedon in China. Em CHINA SEA f"t,.. ",.rti""... w w en "ti :;c 00 -~ -);g i " I,- J _> SI"IC.I.t.II Q UIQI\IJ1l,"U10"0Iol OU S Il~QIO" """ 0"'0 LEGEND Soil with Guanyu epipedon Soil with DUidian epipedon A Soil with Pore-crust epipedon

6 34 SOIL SURVEY HORIZONS 1. Color value >5.5 dry, > 3.5 moist, and organic matter content 0.5 to 20/0. 2. < lo-cm thick. 3. < 2 mm fine-pores dominant in the pore-crust layer, > 14 pores I cm Soluble salts within layer are one-third lower than underlying layer. 5. Moist < 90 consecutive days during a year. Desert areas occupy about one-fifth of the total area of China and are concentrated in the northwest part of the country (Fig. 3). Parent material on hills and low mountains is residuum and sediments derived from residuum. On plains, it is alluvium and loessial deposits. Climate Precipitation is < 200 mmlyr and in some areas < 100 mm/yr. Evaporation is 10 times higher than precipitation. Annual average temperature is 5 to 12 C. The difference between the maximum and minimum temperature is 30 to 50 C in a year and 10 to 15 C in a day. Annual average wind speed is 1.5 to 5 mls with a maximum speed of >20 m/s. There is severe wind erosion with removal of fine earth material and concentration of coarser material. Vegetation is small desert shrubs. Processes 1. Surface horizon accumulation of carbonate ranging from 6 to 9%. 2. Accumulation of gypsum (CaSO.) and soluble salts with NaCl dominant. 3. Concentration of gravel in surface horizon (excluding loess parent material), decreasing amounts of gravel in the subsoil and variable according to parent material. References Gong Zitong, Lei Wenjin, and Xiong Guoyan International tendency of soil classification studies. (In Chinese.) Prog. Soil Sci. 14(1):1-13. Nanjing Institute of Soil Science. Academia Sinica Soils of China. 2nd ed. Science Press, Beijing. Northeastern Institute of Forest Soil Science. Academia Sinica Soils of northeast China. Science Press, Beijing. Soil Classification Group of Nanjing Institute of Soil Science. Academia Sinica Preliminary draft of Chinese soil taxonomy system. (In Chinese.) Soil Sci. 6: Soil Survey Staff Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. USDA-SCS Agric. Handb U.S. Gov. Printing Office, Washington, DC.

Soil Resources. Soil Horizons

Soil Resources. Soil Horizons Soil Resources Soil Uppermost layer of earth s crust that supports plants, animals and microbes Soil Forming Factors Parent Material Time Climate Organisms Topography Soil Composition Mineral Particles