Net global warming potential of spring wheat cropping systems in a semiarid region

Authors: Liebig, Mark; Archer, David; Halvorson, Jonathan; Johnson, Holly; Saliendra, Nicanor; GROSS, JASON - Us Forest Service (FS); TANAKA, DON - North Dakota State University

Submitted to: Land
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2019
Publication Date: 2/8/2019
Citation: Liebig, M.A., Archer, D.W., Halvorson, J.J., Johnson, H.A., Saliendra, N.Z., Gross, J.R., Tanaka, D.L. 2019. Net global warming potential of spring wheat cropping systems in a semiarid region. Land. 8(2):32. https://doi.org/10.3390/land8020032.
DOI: https://doi.org/10.3390/land8020032

Interpretive Summary: Previous studies of net global warming potential (GWP) for crop production in semiarid regions have focused on effects of individual management practices (e.g., tillage, crop rotation, nutrient management, residue removal, etc.). Few studies have considered combined cropping system effects. The goal of this study was to determine net GWP for three wheat-based no-till cropping systems in southcentral North Dakota. Calculated emissions from inputs and field operations were combined with field measurements of methane and nitrous oxide fluxes and changes in soil organic carbon (SOC) to estimate net GWP. Net GWP was positive for spring wheat-fallow and continuous spring wheat, implying net greenhouse gas (GHG) emission to the atmosphere, while net GWP for spring wheat-safflower-rye was negative, implying net GHG uptake. This information is useful to farmers in semiarid regions in selecting practices to reduce GHG emissions, as well as policy makers by showing the challenges in creating cropping systems that reduce GHG emissions. Study outcomes are also useful to scientists in targeting research toward new technology and methods to improve efficiency of nitrogen fertilizer use and management practices that increase SOC.

Technical Abstract: Investigations of global warming potential (GWP) of semiarid cropping systems are needed to ascertain agriculture’s contributions to climate regulation services. This study sought to determine net GWP for three semiarid cropping systems under no-tillage management in the northern Great Plains of North America: spring wheat (Triticum aestivum L.) – fallow (SW-F), continuous spring wheat (CSW), and spring wheat – safflower (Carthamus tinctorius L.) – rye (Secale cereale L.) (SW-S-R). Management records, coupled with published carbon dioxide (CO2) emission estimates, were used to determine emissions from production inputs and field operations. Static chamber methodology was used to measure soil-atmosphere methane (CH4) and nitrous oxide (N2O) fluxes over a 3-year period, and changes in profile soil organic carbon (SOC) stocks were determined over 18 years. Carbon dioxide emissions associated with production inputs and field operations were greatest for CSW, intermediate for SW-S-R, and lowest for SW-F. All cropping systems were minor CH4 sinks (=0.5 kg CH4-C/ha/yr) and moderate N2O sources (1.0 to 2.8 kg N2O-N/ha/yr). No differences in SOC stocks were observed among cropping systems (P=0.78), nor did SOC stocks change significantly from baseline conditions (P=0.82). Summing across factors, net GWP was positive for SW-F and CSW, implying net greenhouse gas (GHG) emission to the atmosphere, while net GWP for SW-S-F was negative, implying net GHG uptake. Net GWP, however, did not differ among cropping systems (P=0.17). Management practices that concurrently improve N use efficiency and increase SOC stocks are needed for semiarid cropping systems to be net GHG sinks.