Dryland Soil Greenhouse Gases and Yield‐Scaled Emissions in No‐Till and Organic Winter Wheat–Fallow Systems

Abstract

Core Ideas Dryland organic and no‐till wheat‐fallow systems impact GHG and wheat yields. The organic system produced more wheat grain yield than the no‐till system in a dry year. The organic system had greater GHG emissions during the fallow period. Concerted effort toward reducing tillage is needed to reduce overall GHG emission in dryland organic wheat–fallow systems. In the semiarid central Great Plains of the United States, cropping intensification beyond the traditional winter wheat (Triticum aestivum L.)–fallow rotation along with reduced tillage can lead to soil organic matter (SOM) conservation and offset greenhouse gas emission. Here, we quantified (i) soil greenhouse gas (GHG) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes, and (ii) yield‐scaled GHG emissions from dryland no‐till (NT) and organic production systems in western Nebraska over a 2‐yr period. The systems evaluated were no‐till winter wheat–proso millet (Panicum miliaceum L.)–fallow (NT 3 yr), no‐till winter wheat–millet–fallow–winter wheat–sunflower (Helianthus annuus L.)–fallow (NT 6 yr), and organic winter wheat–millet or sunflower–fallow (Organic 3 yr). In 2012 and 2013, CO2 and N2O fluxes in the winter wheat phase were generally higher in the no‐till systems relative to the Organic 3‐yr system. In the fallow phase, however, these fluxes were higher in the Organic 3‐yr system than in the NT 6‐yr system, suggesting greater mineralization under the former. In 2013, fluxes of CH4 in the winter wheat phase tended to be higher in the Organic 3‐yr system than in the no‐till systems. Compared with the NT 6‐yr system, the Organic 3‐yr system had lower yield‐scaled emission in the winter wheat phase in 2012 (0.026 vs. 0.014 Mg [CH4 + N2O] in CO2 equivalent Mg−1 yield). More effort toward reducing tillage‐caused soil disturbance intensity is needed to further reduce CO2 and N2O emissions and SOM depletion in dryland organic winter wheat–fallow production systems.