A study on the soil respiration of alfalfa field in the loess hilly region

Carbon cycle process in ecosystem can be influenced by land use change. After implementing the project of farmlands converted to woodland and grassland in China, a large volume of farmland have been changed into woodland and grassland. In order to study the change of carbon emissions after the abandoned project, soil respirations of alfalfa field (converted from farmland) grassland, and farmland were measured in the loess hilly region of south Ningxia. The results indicated that soil temperature was strongly correlated with soil respiration, and the influence of soil moisture on soil respiration was limited. Average values of soil respiration on the alfalfa field, farmland and grassland were 1.60, 1.03 and 0.85 molm-2s-1, respectively. The soil respiration of alfalfa field, compared with farmland and grassland, were 55.3% and 88.2% higher. Annual CO2 emissions of alfalfa field, farmland and the grassland were 1461.96, 940.66 and 777.36 gm-2a-1,respectively. We concluded that after 9 years of farmland converted into alfalfa field, soil organic carbon decreased and soil respiration increased. The contributions of increasing carbon sink in the stage of farmland converted to grassland were not good as expected.