Contribution of winter soil respiration to annual soil CO 2 emission in a Mollisol under different tillage practices in northeast China

Winter soil CO 2 emission is a very important component of the annual carbon budgets, however, almost no information on winter CO 2 emission is available from the cropland soil in northeast China. In this study, soil CO 2 flux was measured for a 2‐year period from an ongoing tillage trial on Black soil in northeast China to quantify seasonal patterns in soil CO 2 flux rate and wintertime contribution to annual soil respiration. Average soil CO 2 flux rates in the winter (November to March) were between 0.64 to 1.22 g CO 2 m −2 d −1 , in the non‐growing season (October and April) were 2.09–3.56 g CO 2 m −2 d −1 , whereas in the growing season (May to September) they were between 10.9 to 12.7 g CO 2 m −2 d −1 , with no significant differences among tillage treatments. Total winter, non‐growing and growing season soil CO 2 emissions were 0.28–0.45 Mg C ha −1 , 0.36–0.53 Mg C ha −1 , and 4.52–5.55 Mg C ha −1 , respectively, among tillage treatments. The contributions of winter soil respiration to annual soil CO 2 emission ranged from 5.1 to 7.1%, and the non‐growing season emission ranged from 11.4 to 15.2% among tillage treatments. Our results indicate that in northeast China, cropland Black soil continuously emits CO 2 throughout the non‐growing season, and the wintertime soil respiration plays a significant role in annual soil carbon budgets. Hence winter soil CO 2 emission must be taken into consideration when the role of the soil ecosystem is assessed as either a sink or source of CO 2 to the atmosphere.