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Pak. J. Bot., 47(5): 1865-1874, 2015.

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SHEEP GRAZING STIMULATED PLANT AVAILABLE SOIL NITRATE ACCUMULATION IN A TEMPERATE GRASSLAND

JINCHAO FENG^1,5, XU HAN², NIANPENG HE³, YUNHAI ZHANG^1,*,LISHI ZHOU¹ AND XINGGUO HAN^1,4,*

Abstract: We investigated the effects of increasing grazing I ntensities on N availability (inorganic N, In-N, for plant and microbial growth, e.g., NO₃^––N, NH₄⁺–N) and variability in soils of 0–10 cm depth during 2009–2010, within a framework of a long-term grazing study. The results showed that the relationship for grazing intensity with respect to soil NO₃^––N (R² = 0.988, P = 0.006) was well depicted by curvilinear equations. Moreover, soil NO₃^––N, NH₄⁺–N and inorganic N varied significantly with sample date, year, and soil water content (SWC, %). There were also significant correlation between date and grazing intensities on soil NO₃^––N, NH₄⁺–N and In-N. SWC and temperature had more impact on soil available N than grazing, especially with respect to the seasonal dynamics of the soil N pool. Grazing intensity, in combination with SWC (precipitation) and temperature, controlled soil N availability and, therefore, affect the N cycles and plant growth within semiarid grasslands.

Key words: Grassland; N availability; N cycle; Sheep; Soil moisture; Stocking rate.

¹State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China

²College of Forestry, Shandong Agricultural University, Taian, Shandong, 271018, China

³Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101 China

⁴State Key Laboratory of Forest and Soil Ecology, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China

⁵ University of Chinese Academy of Sciences, Yuquan Road, Beijing 100049, China,

^*Corresponding authors e-mail: zhangyh670@ibcas.ac.cn; xghan@ibcas.ac.cn