Soil CO2 efflux dynamics in an integrated crop–livestock system

Abstract

Integrated crop–livestock (ICL) systems have shown potential to provide a variety of environmental benefits including soil carbon (C) increases relative to conventional row cropping systems. However, studies documenting C dynamics of ICL systems in the northern Great Plains are lacking relative to other agroecosystems. Soil carbon dioxide (CO₂) efflux, crop biomass, and soil organic matter (SOM) pools were monitored over 3 years in an ICL rotation (corn [Zea mays L.]/soybean [Glycine max L.]–spring wheat [Triticum aestivum L.] + cover crop–cover crop) with fall grazing, a conventional cropping system rotation (corn–spring wheat–soybean) and fall grazed and ungrazed mixed-grass pasture near Mandan, ND. Cropped treatments were under no-till management. Annual aboveground crop residue biomass C was similar in the ICL and conventional systems, while less in the grazed pasture (4.18, 3.83, and 1.21 Mg C ha⁻¹ year⁻¹ respectively; p = 0.039). Annual soil CO₂ efflux was greater in the ICL, grazed, and ungrazed pasture systems than the conventional system (8.05, 8.73, 8.25, and 5.81 Mg C ha⁻¹ year⁻¹, respectively; p < 0.001). Among crop phases in the ICL and conventional cropping systems, cover crops contributed to greater CO₂ efflux in the spring and fall. SOM and C mineralization were greater at 0–5 cm in the ICL system compared to the conventional cropping system (6.6% vs. 6.3%, p = 0.028 and 248 vs. 184 mg CO₂–C kg⁻¹, p < 0.001, respectively). Interseeded cover crops in ICL systems can contribute increased root respiration and enhanced SOM pools relative to conventional cropping systems under semiarid conditions.