Cover crop and tillage systems effect on soil CO2 and N2O fluxes in contrasting topographic positions

Soils are important sources of CO2 and N2O emissions to the atmosphere. Introducing cover crop and conservation tillage are among the strategies to improve soil organic carbon (SOC) and nitrogen (N) sequestration potentials with potential to reduce the amounts of greenhouse gases (GHG) emitted from soil. The objectives of the study were to evaluate CO2 and N2O emissions in rye cover crop and tillage system treatments in contrasting topographical positions. Two replicated field experiments were established in 2011 at Kellogg Biological Station and Mason Research Farm sites, located in Southwest and Central Michigan, respectively. At each site, two replications of three contrasting topographical positions, namely depression, slope and summit were used. The two studied factors were tillage system (chisel plow and ridge tillage) and winter rye cover crop (present and absent). Topographical positions significantly affected the performance of rye cover crop with above ground biomass ranged from 80 to 200kgha−1 and 120 to >500kgha−1 in depressions and summits, respectively. The presence of rye cover tended to increase CO2 emissions across all topographical positions. However, the amount of increases in the CO2 emissions was ∼15mgm2h−1 and <5mgm2h−1 in depressions and summits, respectively, which were inversely proportional to the amount of rye biomass inputs. Ridge tillage had significantly higher CO2 emissions than chisel tillage in depressions and showed increasing trends at the slopes and summits. Neither the effect of cover crop nor tillage system was found to be statistically significant across the whole study period on N2O emissions. Regression analysis indicated that both CO2 and N2O emissions were positively associated with soil temperature. The effect of temperature on CO2 emissions was most pronounced in management treatments with cover crops and in topographical depressions. Per a unit increase in the soil temperature was a greater increase in the CO2 emission in depression areas than other parts of the landscape. The results of the present study highlight existence of complex interactive influences among cover crop presence, tillage, and topography driven variations in soil properties on the resulting soil GHG emissions.