中文摘要：

【目的】在退耕草地实施合理放牧,有助于减少土壤CO_2排放、减缓土壤侵蚀。为验证此假设,本研究选择黄土高原渭北旱原坡地,建立退耕草地放牧、退耕草地不放牧和传统农业耕作三种处理的对比试验小区,定量研究了退耕草地合理放牧相对于退耕草地在减少土壤CO_2排放和土壤侵蚀的作用及其影响因素,为探寻在我国西部退耕还草区实施畜牧业生产与环境保护的协调发展模式提供科学依据。【方法】在建立的退耕草地放牧、退耕草地不放牧和传统农业耕作3种处理的试验小区,利用LI-8100碳通量自动测量仪原位监测植物生长期（4 8月）和放牧前后土壤CO_2排放速率的变化,同时利用时域反射仪（TDR）测定表层0—10 cm土壤含水量,用地温表测定土壤表层2 cm和5 cm的温度。利用环境放射性核素7Be示踪技术监测较大降雨事件引起的土壤侵蚀速率,同时取样测定侵蚀区土壤有机碳含量,比较不同处理小区侵蚀导致的土壤有机碳流失量。【结果】观测期间,3种处理CO_2平均排放速率大小顺序为退耕草地[3.69±0.39μmol/（m-2·s）]〉退耕草地放牧[3.00±0.44μmol/（m-2·s）]〉传统农耕地[1.99±0.22μmol/（m-2·s）],坡耕地退耕还草后土壤CO_2排放增加了85%,而合理放牧使退耕草地土壤CO_2排放量减少了19%。放牧后退耕草地土壤CO_2排放速率平均减少了11%,减少值在2%41%之间。观测期内,退耕草地放牧后土壤侵蚀速率比农耕地和退耕草地分别减少了93%和77%。坡耕地退耕还草后土壤CO_2排放增加主要由于草被植物引起土壤有机碳储量增加和土壤侵蚀强度减小,放牧后退耕草地土壤CO_2排放减少主要与动物踩踏引起土壤容重明显增加及草类植被地上部分向土壤中输入的有机碳的减少有关。水分、温度影响因子无法解释3种处理间土壤CO_2排放差异。【结论】合理放牧不仅能显著减少退耕草地土?

英文摘要：

【Objectives】Reasonable grazing on grain for green grassland is considered helpful for reducing soil CO_2 emissions as well as soil erosion. In order to verify this hypothesis,we set up three treatments at our study site- a slope on the Weibei Loess plateau-in order to investigate the effect of reasonable grazing on soil CO_2 emissions and soil erosion. Additionally,we hope this study can provide a scientific basis for the coordinated development of livestock production and environmental protection in Chinese western grain for green grassland. 【Methods】Thethree treatments used in our study were 1） grain for green grassland with grazing（ G ＋ G）,2） grain for green grassland without grazing（ G- G） and 3） conventional tillage（ CT）. Soil CO_2 emission rates were automatically monitored by a LI-8100 carbon flux measuring instrument in situ,with soil moisture content measured by TDR and soil temperature measured by a thermometer. The environmental radioactive nuclide,7Be,was used as a tracer for the soil erosion rate following heavy rainfall. 【Results】During the test period,average CO_2 emission rates of these3 test plots were as follows： G- G [3. 69 ± 0. 39 μmol /（ m-2·s）] G ＋ G [3. 00 ± 0. 44 μmol/（m-2·s）] CT[1. 99 ± 0. 22 μmol/（m-2·s）]. Soil CO_2 emission in G- G was 85% more than CT,whilst soil CO_2 emission rate in G ＋ G was 23% less than G- G. Grazing activity was found to significantly reduce soil CO_2 emission rates in G＋ G by 2%- 41%,with the average of 11%. During the observation period,the soil erosion rate in the G ＋ G plot was significantly less than that observed in both CT and G- G,by 93% and 77%,respectively. Compared to CT,the increased soil CO_2 emissions observed in G- G was due to increased SOC,whilst for G ＋ G this was due to decreased soil erosion. Trampled ground as a result of animal grazing led to a significant increase in soil bulk density with a concomitant reduction in the amount of organic carbon entering the soil. Both of these