Experimental investigation on soil carbon, nitrogen, and their components under grazing and livestock exclusion in stepp
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ORIGINAL ARTICLE
Experimental investigation on soil carbon, nitrogen, and their components under grazing and livestock exclusion in steppe and desert steppe grasslands, Northwestern China Haiyan Wen • Decao Niu • Hua Fu Jian Kang
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Received: 15 November 2011 / Accepted: 1 March 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Livestock grazing is one of the main causes for the change of soil organic carbon (SOC) and total nitrogen (TN) in the arid and semi-arid parts in northern China. This paper examined the SOC, TN, and their components of the local steppe and desert steppe, considering continuous grazing and 4-year livestock exclusion, respectively. In steppe where livestock is excluded, both SOC and TN in the topsoil (0–0.20 m) are found to remain unchanged; however, significant growths are found in microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), particulate organic carbon (POC), and particulate organic nitrogen (PON). On the contrary, both POC and PON progressively decrease at the continuous grazing sites, attributed to the reduction of the mass proportions of soil particulate fraction in the top 0.10 m soil. In the desert steppe where grazing is excluded, the SOC, TN, and their components of the topsoil increase. However, at the continuous grazing sites, POC and PON in the 0.10 m topsoil are reduced, caused by the decrease of C and N content in soil particulate fraction. Besides, microbial quotients were lower in the continuous grazing sites in the two grasslands. It is also found that both MBC and POC are more sensitive to human-induced activities than SOC, and thus could serve as earlier indicators of the soil-fertility variation caused by short-period grazing management.
H. Wen D. Niu H. Fu (&) State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, Gansu 730020, China e-mail: [email protected] J. Kang School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou, Gansu 730050, China
Keywords Soil organic carbon Total nitrogen Soil carbon and nitrogen components Grazing management Steppe Desert steppe
Introduction Soil organic carbon (SOC) is critical to the global carbon (C) cycling and balances as it acts as a large C reservoir (IPCC 2007). The SOC in grassland counts for 15.2 % of the terrestrial C storage (Houghton 1995), playing an important role on the global carbon cycling and balances (Schuman et al. 1999). Soil total nitrogen (TN) is a foundation of soil N fertility and a particularly important soil-quality attribute (Wang et al. 2004). Grassland SOC and TN variations resulting from grazing have gained many researches in recent years but have led to variant conclusions because of different grassland-types and -managements. No significant SOC change is found in two semi-arid grasslands in the northwestern Australia after heavy grazing for 6–8 years (Holt 1997), similar to the conclusions drawn from other grasslands (Milchunas and Lauenroth 1993). Other diff
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