Greenhouse Gas Fluxes and Soil Carbon and Nitrogen Following Single Summer Tillage Event

Abstract

No-till farming results in gradual buildup of soil organic matter (SOM) and re-introduction of tillage can often reverse it. However, tillage in low precipitation regions may be needed to manage weeds and disperse accumulation of immobile soil nutrients. The main objective of this study was to assess the effects of a single summer tillage on carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), soil water filled pore space (WFPS), dissolved organic carbon (DOC) and nitrate (NO3) in winter wheat - summer fallow systems that were either tilled for the first time after nine years of no-till (NTT), not-tilled (no-till, NT) or were frequently tilled (conventional, CT; and organic, CF). The study was established in the US Central High Plains region where annual precipitation averaged 332±39 mm. Soil and gas samples were collected before the tillage event (time zero) and at 1hr, 5 hrs, 25 hrs and 50 hrs after. Immediate increases in CO2 and N2O fluxes were observed in all tilled treatments within the first 1 to 5 hours but 50-hr cumulative N2O and CO2 in NTT did not differ from the values observed in NT. Tillage however, resulted in a 22% greater 50-hr cumulative CH4 assimilation in NTT compared with NT and was comparable with CH4 in CT suggesting enhanced soil aeration. Soil NO3 did not change in NTT unlike in CT and CF and soil DOC did not increase in NTT until 25 hrs after when, it returned to levels comparable with time zero. In contrast, DOC in CT and CF continued to stay elevated after 50 hrs. In conclusion, single tillage event of a long-term no-till performed on dry soil during summer did not negate benefits associated with SOM accrual and may be a viable alternative for farmers to address some of the management-related problems.