Carbon footprint and carbon balance of three long-term dryland cropping sequences

Carbon footprints from plants, soil, and the environment are needed to evaluate C balance of an agroecosystem, which indicates if a system is a C source or sink for mitigating climate change. There is scarce information about C footprint and C balance in dryland agroecosystems. We measured C storage of above- and belowground crop biomass, CO₂ fluxes, soil C sequestration rates, and C balances of three long-term (34-year-old) dryland cropping sequences from 2016 to 2018 in the US northern Great Plains. Cropping sequences were no-till continuous spring wheat (NTCW; Triticum aestivum L.), no-till spring wheat–pea (NTWP; Pisum sativum L.), and conventional till spring wheat–fallow (CTWF). Carbon storage in grain, straw, root, and rhizodeposit were 29%–61% greater for NTCW and NTWP than CTWF. The CO₂ flux peaked immediately after tillage, planting, fertilization, and intense precipitation (>10 mm) for 3 months in 2016–2017. Cumulative annual CO₂ flux was 8%–37% greater for NTCW than NTWP and CTWF in 2016–2017, but was not different among cropping sequences in 2017–2018. Soil C sequestration rate at 0–10 cm measured from 2012 to 2019 was in the order: NTCW (0.27 Mg C ha⁻¹ year⁻¹) > NTWP > CTWF (−0.23 Mg C ha⁻¹ year⁻¹). Carbon balance remained negative and was not significantly different among cropping sequences but varied by year. Carbon loss increased with increased precipitation, regardless of cropping systems. Although a C source, the legume–nonlegume rotation can reduce C loss due to greater grain C output than other cropping sequences in the semiarid region of the northern Great Plains.