Effects of tillage system on greenhouse gas fluxes and soil mineral nitrogen in wheat (Triticum aestivum, L.)-fallow during drought

•Drought reduced WFPS by an average of 23%.•First-year drought reduced soil CO2 fluxes but increased N2O fluxes.•Second-year drought increased soil NO3 and reduced N2O fluxes to almost none.•Soil under NT had the lowest CO2, N2O and the highest soil NO3 and water content.•Soil under NT only remained a C sink in the second year.

Recurring drought combined with intensive tillage may accelerate degradation of soils in a soil organic matter (SOM)-loss feedback that undermines agricultural sustainability of semiarid farming systems. Winter wheat (Triticum aestivum, L.) in Wyoming is grown on marginally productive soils and annual precipitation of less than 400 mm. Greenhouse gas (GHG) fluxes, soil nitrogen (N), global warming potential (GWP) and greenhouse gas intensity (GHGI) were monitored in no-till (NT), conventional tillage (CT, four tillage operations), and chemical-free (CF, six tillage operations) for 27 months beginning in May 2011. Severe drought started in April 2012 and lasted 17 months. No-till best mitigated GHG emissions and accumulation of mineral N, emitting 25%-30% less nitrous oxide, 35% less carbon dioxide fluxes and retaining twice as much soil nitrate compared with CT and CF during drought in the summer of 2012. Net GWP and GHGI in NT were 32%-35% and 43% lower than in CT, respectively. NT was the only management system that maintained negative net GWP and GHGI values during the summer of 2013. As drought reduces the amount of residue inputs and SOM restorative processes, reducing tillage frequency and leaving more crop residue after harvest support more effective SOM protection during drought.