ZHOU Zhi-hong1,2, LEE Xin-qing1,WANG Bing 1,CHENG Jian-zhong1, CHENG Hong-guang1, YANG Fang1,2 ,JIANG Wei1,2, YAN Hui1,2
(1.State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
2. Graduate University of Chinese Academy of Sciences, Beijing 100049, China)
Abstract: Ammonia volatilization is the major process for the loss of N after the application of N-fertilizers to agricultural soils and pastures. It is also suggested to be true to N loss in the undisturbed grassland in the arid and semi-arid areas of the world. This belief, however, falls short of field examination. China covers about 1.5 million square kilometers of steppe in the arid and semi-arid areas in the north, of which the Agriculture-Pasture Transition Zone (APTZ) is found to be deficit in soil N relative to organic C. Understanding the role played by ammonia volatilization in N depletion is helpful with the remediation and prevention of soil degradation, and thus with the safeguarding of ecological security in North China. This study measured the diurnal variation of NH3 flux during August 2010 in the APTZ in the northwestern front of the loess plateau and the mid and west Ningxia Autonomous Region. In-situ measurement was fulfilled using a Thermo-Fisher Model 17i chemoluminescence NOx-NH3 analyzer and the flux was estimated in conjunction with a dynamic chamber. The results indicated that the diurnal flux varies in four types, averaging between -2～2mgNH3/（m2·h）. The flux is negative, an indication of net deposition of NH3 from air to soil, on the western edge of the Mu Us Sandy land, and after a transition in the mid and west Ningxia, it becomes positive, a net release of soil NH3 to the air, in southern Ningxia. The southward increase of NH3 flux is the result of the moistening effect of precipitation, which is made by the dry environment, a key factor to others such as the temperature and pH of the soil. These results suggested that ammonia volatilization is not important in N loss to the soils of the grassland in the arid and semi-arid areas of North China, thus it may not have caused the relative deficit of the nutrients relative to C.
Key words: arid area; grassland; nitrogen cycle; ammonia volatilization; gaseous loss
EARTH AND ENVIRONMENT Vol. 39, No.3, Tot No.285, 2011, Page 292-299
