Isolation and Identification of Soil Organic Matter in Inner Mongolia Grassland

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the National Natural Science Foundation of China (No. 41471198) and the National Key Basic Research Program of China (No. 2014CB138801)

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    【Objective】Inner Mongolia grassland is not only one of the important meat and milk production areas of China, but also an important ecological barrier in North China. In recent decades, in addition to global climate warming and continuous drought, unreasonable use of the land resources has caused severe degradation of the grassland, and reduction of the soil’s capacity of accommodating rain water. Consequently, the soil is becoming more and more water repellent. In order to find out causes of water repellency and to help to solve the problem, it is necessary to get to know exactly distribution, species and content of the soil organic matter in the grassland, and especially relationship of the organic compounds with soil water repellency, so as to facilitate monitoring and eliminating soil water repellency. The purpose of this paper is to establish a method for separation and purification of soil organic compounds in the grassland, to obtain some certain-structured organic matter, and to lay down some foundations for further studies on relationship of the organic compounds with soil water repellency.【Method】In this paper, soil samples were collected from the surface soil layer (0~5cm) of a tract of forage grassland in the south of Xilinhot city, Inner Mongolia and petroleum ether, chloroform, isopropanol, methanol, isopropanol/acetic acid(7:3), isopropanol/ammonia (7:3), different in polarity were used as extraction agent for ultrasonic extraction of the soil samples. Crude extracts were tentatively identified with UV, IR and GC-MS, and then processed with column chromatography to get different species of organic compounds. 【Result】The following findings were obtained. The crude extract, using isopropanol/ammonia, isopropanol/acetic acid as extraction agents was quite large in quantity, while those using petroleum ether, chloroform, isopropanol and methanol as extraction agents was less. The extracts using different solvents differed in appearance, the crude extracts using petroleum ether, chloroform, and isopropanol appeared to be yellow; while those using isopropanol/acetic acid and isopropanol/ammonia, dark brown. The UV-Vis absorption wavelengths of all the crude extracts were concentrated in the range of 200~480 nm. The crude extracts, though using different extractants, were basically quite similar in infrared spectrum, but their chief absorption peak appeared separately at 2 960 cm−1, 2 920 cm−1, 2 850 cm−1 (C-H stretching vibration), 1 732 cm−1 (C=O) 1 460 cm−1 and 1 375 cm−1 (C-H, C-C bending vibration). Besides a relatively weak absorption peak was observed in the vicinity of 1 667 cm-1, in the IR spectra of the crude extract using methanol and isopropanol/ammonia and isopropanol/acetic acid, reflecting the existence of aromatic skeleton or amide associated with a C=O double bond. Comparison between the GC-MS of the crude extracts and the standard mass spectra reveals that hydrocarbons made up about 95% of the crude extract using petroleum ether, isopropanol or methanol extract, and only about 70% of the total extract using isotropanol/ammonia or isopropanol/acetic acid extracts, and both were dominated with C2323 linear hydrocarbon. Steroid (mainly sitosterol) was only detected in the crude extracts using chloroform, isopropanol/ammonia and isopropanol/acetic acid. The crude extract using isopropanol/ammonia was further separated and purified with column chromatography, and then two portions of substances displaying Rf=0.56 and 0.21(A, B) (petroleum ether: ethyl acetate = 4: 1), respectively, were obtained on the plate. In the GC-MS spectra, the retention time of the compound in Part A varied mainly in the range of 30 ~ 34 min, while that in Part B mainly in the range of 25 ~ 30 min.【Conclusion】The crude extract using petroleum ether, isopropanol or methanol as extractant was composed mainly of linear or cyclic hydrocarbons; and that using chloroform, isopropanol/acetic acid (7:3) or isopropanol/ammonia (7:3) mainly of esters, amides and steroids besides in addition to linear or cyclic hydrocarbons. The crude extract using isopropanol/ammonia (7:3) was separated into Part A and Part B with column chromatography. Part A was identified as steroidal ketones, and Part B as oxygen-free sterenes or sterols with GC-MS and MS library search.

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LIU Shenglan, LIU Honglin, A Lamusi, LI Jiarong, ZHAO Zhangtao, ZHANG Qi, WU Hongxin, WANG Hai, JI Lei, QIN Yan. Isolation and Identification of Soil Organic Matter in Inner Mongolia Grassland[J]. Acta Pedologica Sinica,2017,54(6):1459-1470.

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  • Received:December 23,2016
  • Revised:June 11,2017
  • Adopted:July 25,2017
  • Online: September 04,2017
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