DAILY AND SEASONAL VARIATION OF SOIL RESPIRATION OF FARMLAND IN THE TIBETAN PLATEAU

Soil respiration of different farmlands were measured and the characteristics of its daily and seasonal variation were identified for the farmlands of winter wheat, Tibet barley and non-crop soil in the Tibetan Plateau. The maximum and minimum soil respiration of winter wheat farmland, Tibet barley farmland and non-cropland occurred at local time 13:00～14:00 and 5:00～6:00 respectively. However, soil respiration in winter was fairly low and daily variation was not apparent. Soil respiration in winter and Tibet barley farmland reached maximum values in the grouting period in a year, accounting for 40 g·m -2·d -1. After harvest, soil respiration, including microorganism and root respiration, gradually reduced to less than 20 g·m -2·d -1 with the air and soil temperature decrease. In winter, soil respiration lessened to some 2 g·m -2·d -1. Soil CO 2 emission was more correlative to 5 cm soil temperature than soil temperature of other layers. Therefore, 5 cm soil temperature can be used for estimating amount of soil respiration. 5 cm soil temperature in growing season and non-growing season were used to separate root respiration from total soil respiration. The ratio of root respiration is 34～44%,averaging 40%.