Dryland Soil Greenhouse Gases and Yield-Scaled Emissions in No-Till and Organic Winter 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.