Carbon dioxide flux as affected by tillage and irrigation in soil converted from perennial forages to annual crops

Among greenhouse gases, carbon dioxide (CO2) is one of the most significant contributors to regional and global warming as well as climatic change. A field study was conducted to (i) determine the effect of soil characteristics resulting from changes in soil management practices on CO2 flux from the soil surface to the atmosphere in transitional land from perennial forages to annual crops, and (ii) develop empirical relationships that predict CO2 flux from soil temperature and soil water content. The CO2 flux, soil temperature (Ts), volumetric soil water content (θv) were measured every 1–2 weeks in no-till (NT) and conventional till (CT) malt barley and undisturbed soil grass-alfalfa (UGA) systems in a Lihen sandy loam soil (sandy, mixed, frigid Entic Haplustoll) under irrigated and non-irrigated conditions in western North Dakota. Soil air-filled porosity (ε) was calculated from total soil porosity and θv measurements. Significant differences in CO2 fluxes between land management practices (irrigation and tillage) were observed on some measurement dates. Higher CO2 fluxes were detected in CT plots than in NT and UGA treatments immediately after rainfall or irrigation. Soil CO2 fluxes increased with increasing soil moisture (R2=0.15, P<0.01) while an exponential relationship was found between CO2 emission and Ts (R2=0.59). Using a stepwise regression analysis procedure, a significant multiple regression equation was developed between CO2 flux and θv, Ts (CO2 flux = e - 3.477 + 0.123 T s + 6.381 θ v ; R2=0.68, P⩽0.01). Not surprisingly, soil temperature was a driving factor in the equation, which accounted for approximately 59% in variation of CO2 flux. It was concluded that less intensive tillage, such as no-till or strip tillage, along with careful irrigation management will reduce soil CO2 evolution from land being converted from perennial forages to annual crops.