Long-term continuous cropping reduces greenhouse gas emissions while sustaining crop yields

Information is needed on the effect of long-term cropping systems on greenhouse gas (GHG) emissions in dryland conditions. The effect of 34 years of dryland cropping system was examined on N₂O and CH₄ emissions, greenhouse gas balance (GHGB), crop yield, and yield-scaled GHG balance (YSGB) from 2016–2017 to 2017–2018 in the US northern Great Plains. Cropping systems 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). Gases were sampled twice a week to once a month throughout the year using a static chamber and flux determined. Soil C sequestration rate at 0–10 cm was determined from samples taken in 2012 and 2019. The N₂O emissions occurred immediately after planting, fertilization, and intense rainfall from May to September in both years when the emissions greater for NTCW and NTWP than CTWF. The CH₄ emissions were minimal and mostly negative throughout the year. Carbon sequestration rate was positive for NTCW and NTWP due to greater C input, but negative for CTWF due to rapid C mineralization. As a result, GHGB was 170%–362% lower for NTCW than NTWP and CTWF. Annualized crop yield was 23%–60% greater for NTWP than NTCW and CTWF in 2016–2017, but not different among cropping systems in 2017–2018. The YSGB was also 129%–132% lower for NTCW and NTWP than CTWF in both years. Because of greater annualized crop yield, but lower GHG emissions, NTWP is recommended for reducing GHG emissions while sustaining long-term dryland crop yields in the northern Great Plains.