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. Long-term crop-fallow reduced N2O flux compared to continuous cropping. The CH4 flux was not affected by cropping system. Long-term continuous cropping increased soil carbon sequestration rate compared to crop fallow. As a result, long-term continuous cropping reduced greenhouse gas emissions per unit area and per unit crop yield. Long-term legume-nonlegume rotation can reduce greenhouse gas emissions while sustaining crop yields. Conventional till crop-fallow has been a traditional dryland cropping systems in the northern Great Plains. There is a lack of information about how long-term conventional till crop-fallow system affect greenhouse gas emissions compared to no-till continuous cropping systems. Scientists at ARS, Sidney, MT, studied the long-term effect of continuous till spring wheat-fallow, no-till continuous spring wheat, and no-till spring wheat-pea rotation on greenhouse gas emissions from 2016 to 2018. They reported that no-till continuous spring wheat and no-till spring wheat-pea reduced greenhouse gas emissions per unit area as well as per unit crop yield compared to continuous till spring wheat-fallow due to increased carbon sequestration. However, crop yields were lower for continuous spring wheat than spring wheat-pea rotation. Therefore, they recommended that no-till spring wheat-pea rotation can reduce greenhouse gas emissions while sustaining long-term crop yields in the northern Great Plains.