Reasonable grazing on grain for green grassland on Loess Plateau can reduce soil CO₂ emission and soil erosion

【Objectives】 Reasonable grazing on grain for green grassland is considered helpful for reducing soil CO2 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 CO2 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】 The three 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 CO2 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 CO2 emission rates of these 3 test plots were as follows: G-G 3.69± 0.39 μmol/(m2·s)G+G 3.00± 0.44 μmol/(m2·s)CT 1.99± 0.22 μmol/(m2·s). Soil CO2 emission in G-G was 85% more than CT, whilst soil CO2 emission rate in G+G was 23% less than G-G. Grazing activity was found to significantly reduce soil CO2 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 CO2 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 factors led to the reduction of soil CO2 emissions in G+G. However, the difference of soil CO2 emissions among these three plots could not be explained by soil moisture and temperature. 【Conclusions】 Our study found that reasonable grazing activity would not only decrease the soil CO2 emissions, but also could effectively control soil erosion and SOC loss, which would in turn facilitate the increase of the soil carbon reserve. Trampled ground from animal grazing can lead to an increase in soil bulk density, a major contributing factor for the reduction in soil CO2 emissions and soil erosion rates. Our research revealed that in the Chinese Loess plateau or similar grain for green region, reasonable grazing can not only promote the local livestock production, but also help control soil erosion and reduce CO2 emissions. Thus this has been a worthwhile study for investigating various models of sustainable development for grassland management.