Net global warming potential and greenhouse gas intensity in organic and conventional wheat-based farming systems

There is a need of information about global warming potential in wheat (Triticum aestivum L.)-based organic and conventional farming systems. We evaluated net global warming potential (NGWP) and greenhouse gas intensity (GHGI) in the organic farming system (OFS) using sheep grazing to control weeds without N application and the conventional farming system (CFS) with herbicide, pesticide, and N applications in three crop phases of a 5-yr crop rotation from 2013-2014 to 2015-2016 in the northern Great Plains. Crop phases were winter wheat after lentil (Lens culinaris L.) (W-L), winter wheat after sweet clover (Melilotus officinalis L.) cover crop (W-C), and lentil after winter wheat (L-W) in a 5-yr rotation of safflower (Carthamus tinctorius L.) and sweet clover cover crop intercrop-sweet clover cover crop-winter wheat-lentil-winter wheat. Carbon sequestration rate at the 0-to-120-cm depth from 2009 to 2015 was greater in OFS with W-C than other treatments. The CO2 equivalent of N2O + CH4 fluxes was greater in OFS with L-Wthan other treatments, except in CFS with L-W in 2014-2015 and 2015-2016. The CO2 equivalent of N fertilization was greater in CFS, but CO2 equivalent of CH4 flux due to enteric fermentation from sheep was greater in OFS. Both NGWP and GHGI were lower in OFS with W-C than other treatments. Organic farming system using sheep grazing to manage weeds in winter wheat following cover crop can reduce NGWP and GHGI compared with CFS with chemical inputs in dryland farming.