| With the increase of the concentration of atmospheric greenhouse gases, carbon change in the terrestrial ecosystem has been paid great attention, becoming a hot topic in global research currently. The understanding of the changes in soil carbon precesses and their relations will help us evaluate the role of agricultural practices as carbon sinks/sources in agroecosystems and the impacts of these practices on climate change. The experiments were conducted in Shouyang of Shanxi province, the dry semi-humid area, to determine the changes in crop yields, soil organic carbon, soil respiration and soil microflora under the different nutrient management and tillage practices. Though analyzing soil carbon change related processes, their relations and the major influence factors(such as soil moisture, soil temperature and rainfall), The study explored the soil carbon dynamics affected by nutrient management and tillage practices in the dryland agroecosystem and their contributions to soil carbon sinks/sources.The paper draws the conclusions as follows.1. Soil respiration in the maize field showed a significant seasonal change with soil temperature change: lower in the winter and the spring, higher both in the middle summer and in the beginning of autumn. Soil respiration reached the maximum (1570 CO2-C mg/m2/d) during the peak growing period for spring maize. There was a negative linear correlation between soil respiration and soil water content (0-10 cm); a exponential correlation existed between soil respiration and soil temperature (0-5 cm) in the crop growth period. A positive linear correlation between soil respiration and soil water content (0-10 cm) was found during maize growing season.2. The total amounts of soil respiration with the highest input of maize stover into the soil (fertilizer N 105 kg/ha,straw 6000 kg/ha and manure 1500 kg/ha) under the reduced tillage were the most (2571 CO2-C kg/ha/y). The total amounts of soil respiration with different tillage practices were ranked in order: reduced tillage(2146 CO2-C kg/ha/y)>no tillage (1983 CO2-C kg/ha/y)>conventional tillage (1977 CO2-C kg/ha/y). Soil respiration in maizw growing season accounted for aberver 20%of the total amount.3. The changes in soil microflora and soil respiration rate showed the same trend, in particular, the amounts of bacteria and actinomycetes have the linear correlation with soil respiration rate significantly.4. Partial soil carbon balance analysis showed: the highest input of both stover (2578 kg C/ha) and manure (3709 kg C/ha) had great carbon sinks. Conservation tillage, such as reduced tillage (3631 kg C/ha) /no-tillage (2465 kg C/ha) played the more important role in improving soil carbon sinks, as compared with conventional tillage, which showed as soil carbon resource relatively.5. Long-term reduce tillage combind with balanced fertilization caused the increase in the crop yields. The appliantion of fertilizer N, maize stover, and manure (fertilizer N 105 kg/ha,straw 6000 kg/ha and manure 1500 kg/ha) was optimal for dryland spring maize in Shouyang of Shanxi. Crop yields with conservation tillage practices (reduced tillage /no tillage) were higher than the yield with conventional tillage practice (7.2%-11.7%).The innovention of the study explored the change in soil carbon processes and the potentials of soil carbon sank /resource in dryland agroecosystems, base on the long-term field experiments with nutrient management and tillage practices to provide scientific information for the improvement of carbon management in dryland agroecosystem. |
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