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

Authors: Sainju, Upendra; Allen, Brett

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2024
Publication Date: 5/29/2024
Citation: Sainju, U.M., Allen, B.L. 2024. Carbon footprint and carbon balance of three long-term dryland cropping sequences. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.20703.
DOI: https://doi.org/10.1002/saj2.20703

Interpretive Summary: The approximately 40 million dryland crop acres in the semi-arid region of the northern Great Plains represent a vast area of soil where carbon could be either stored or released into the atmosphere. Crop production practices will determine whether these soils will be a carbon sink that mitigates future climate change or a source of carbon that contributes to rising atmospheric carbon dioxide levels. ARS scientists in Sidney, MT estimated carbon footprints of spring wheat crop production systems in this region of the US based on the amounts of carbon in plants, soil, and the environment as impacted by three dryland cropping systems in a long-term (34 years) cropping systems study. They reported that carbon inputs and outputs were greater in no-till continuous spring wheat, intermediate in no-till spring wheat-pea, and lower in spring wheat-fallow rotations. However, carbon balance was not affected by cropping systems, but remained negative in all systems, indicating that dryland cropping systems were carbon sources. The authors predicted that dryland cropping systems can be carbon sinks if perennial crops, because of their greater root biomass production, are included in rotation with annual crops.

Technical Abstract: Carbon footprints from plants, soil, and the environment are needed to evaluate C balance of an agroecosystem which indicates if a system is C source or sink for mitigating climate change. There is scarce information about C footprints 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 yr) dryland cropping sequences from 2016 to 2018 in the US northern Great Plains. Cropping sequences were no-till continuous spring wheat (Triticum aestivum L.) (NTCW), no-till spring wheat-pea (Pisum sativum L.) (NTWP), and conventional till spring wheat-fallow (CTWF). Carbon storage in grain, straw, root, and rhizodeposition 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 three 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>NTWP>CTWF. Carbon balance remained negative and was not significantly different among cropping sequences, but varied by year. Although a carbon source, legume-nonlegume rotation relatively reduced C loss and enhanced grain C output compared to other cropping sequences in the semiarid region of the US northern Great Plains. Carbon loss increased with increased precipitation.