Impacts of grazing intensity on soil carbon and nitrogen in an alpine meadow on the eastern Tibetan Plateau

Author: Yongheng Gao ^1*, Martin Schumann ², Huai Chen ^{3, 4}, Ning Wu ³ and Peng Luo ³

Received 27 January 2009, accepted 12 April 2009.

Abstract

Different land-use strategies cause changes in soil carbon (C) and nitrogen (N) levels. This study aimed to determine seasonal changes in soil C and N contents and to investigate their transformations under three different grazing intensities (light grazing - LG 1.2, moderate grazing - MG 2.0 and heavy grazing HG 2.9 yaks ha^-1) in alpine meadows on the eastern Tibetan Plateau. This study substantiates significant seasonal differences of soil N contents but not to soil C contents. Averaged soil C and N values of all sampling dates were significantly higher in the HG site than in the LG and MG sites. Soil NO₃^- -N was highest at the HG site in June (8.16 mg kg^-1) and lowest at the MG site in August (4.26 mg kg^-1), while soil NH₄⁺-N was highest at the HG site in August (12.57 mg kg^-1) and lowest at the LG site in June (4.60 mg kg^-1). Over the study period, soil N transformation rates, such as gross rates of nitrification, denitrification and N₂O flux rate increased rapidly from June to July and then decreased until September. Generally, higher grazing intensities seem to cause higher soil N transformation rates. These results indicate that short-term heavy grazing has a better potential for soil C and N sequestration in alpine meadow systems.

Key words: Grassland, carbon, gross nitrification, denitrification, Tibetan Plateau.