| Soil respiration is the key ecological process, which leads to global climate change through releasing CO2 to the atmosphere. Small changes in soil respiration would have a significant impact on the global carbon cycle. With the strongest disturbance of terrestrial ecosystems, agricultural ecosystems could regulate carbon cycle at a short temporal scale. Therefore, in-depth understanding on the soil CO2 efflux from agricultural ecosystem and its controlling mechanism may have important significance on estimating carbon budget accurately, developing adaption strategy to climate change and making CO2 emission reduction decision in China.The long-term experimental site in the arid-highland of the Loess Plateau is located in Changwu County, Shaanxi Province, China (N 35°12, E 107°40). Uneven distribution of precipitation in the area, the soil water deficit limits the improvement of agricultural productivity on one hand, also is the key factor that affect soil CO2 release on the other hand. Surface cover (cover of straw or plastic mulching) can effectively inhibit soil moisture evaporation, increase soil organic matter, increase crop yield and water use efficiency, has become an important technology measures in dryland agriculture cultivation. Mulching on Dryland research more, but for dry farmland after land cover variation of soil respiration and its control mechanisms need further study. This paper was established as a platform under different mulching treatments in the Loess Plateau Area, dynamics and diurnal variations of soil respiration rate under different mulching treatments, and different cover on soil moisture and water use efficiency. The crop used for the experiment is winter wheat.Treatments were two rates of straw mulching (300 [M300] and 600 kg hm-2 [M600]), plastic film mulching (PM) and no mulching (CK). Plastic film mulching did not involved in the first year. The main results are as follows:Four treatments were included for the study as straw mulching at 300 kg hm-2 (M300) and 600 kg hm-2 (M600), plastic film mulching (PM) and no mulching (CK). The soil respiration rate declined from autumn to winter regardless of treatments, while it increased rapidly after winter and peaked at jointing stage. Compared with the control, mulching obviously promoted the soil respiration from wintering to maturing stage, among which PM had markedly significant difference with the other treatments. The average soil respiration rate in the whole growth period, M600(1.47 umol CO2·*m-2·s-1) treatment improved over CK(1.38 umol CO2·m-2·s-1, M300(1.52 umol CO2·m-2·s-1)treatment improved 6.6%, PM(3.63 umol CO2·m-2·s-1) treatment increased 163% compared with CK. The diurnal variation of soil respiration rate for CK presented a single peak curve and peaked at 12:00, while peaks for M300 and M600 were delayed by two hours to 14:00. For PM treatment, the diurnal variation of soil respiration rate was similar with CK at jointing stage but presented a bimodal curve at the maturing stage with the peaks at 12:00 and 16:00, respectively. Soil respiration rate was correlated exponentially with soil temperature and parabolically with soil moisture, Soil respiration showed positive correlation with soil temperature at 5 cm depth, of which 0～10cm layer of soil moisture associated with a higher rate with soil respiration rate.For the agricultural year of 2008-2009, soil water storage at 0～1 m and 0～2 m layer changed in the similar trend after mulching. Compared with the control, two straw mulching treatments had no significant effect on water storage at 0～1 m and 0～2 m soil layer. In terms of yield, CK had the highest value, followed by M600 and M300. The differences in yield among treatments were not significant at 0.05 level. For the second year (2009-2010), soil water storage at 0～1 m and 0～2 m layer in two straw mulching treatments were both higher than that in CK. Straw mulching treatments had a higher water use efficiency and precipitation use efficiency than CK. Compared to CK, treatment M600 and M300 increased crop yield by 7% and 8%, respectively. The difference of water use efficiency and yield between plastic film mulching and control also was not significant.
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