GHG Emissions and Soil C and N Dynamics Following the First Plowing of Long-Term No-till Fallow in Dryland Winter Wheat.

Transitioning to organic winter wheat in dryland climate requires tillage to manage weed population. However, we do not understand the impact of introducing tillage to soil organic carbon (SOC) and nitrogen (N) dynamics while transitioning from long-term no-tillage system to tillage-intensive organic system. Here we report the effects of first tillage of long-term no-till plots on greenhouse gas (GHG) emissions and corresponding changes on SOC and N, and compare it to a similar event under long- term conventional, and long-term organic plots. No-till in transition plots were plowed for the first time after seven years. The treatments were replicated five times. The gas emissions (N2O, CO2, and CH4) from each management scenario were measured before tillage, and at one, five, twenty five and fifty hours following the tillage. Soil samples collected at the time of gas measurement were analyzed for moisture content, inorganic nitrogen, and potentially mineralizable N. Soils tilled after several years of no-tillage had larger flux of CO2 to the atmosphere immediately after tillage compared to conventional and organic system. The cumulative CO2 emissions in transition plots (1163.25 mg C (CO2) m-2 hr-1) within 50 hours of tillage disturbance, however, was lower than long term organic (1808.03 mg C (CO2) m-2 hr-1) and conventional plots (1366.01 mg C (CO2) m-2 hr-1). Cumulative N2O emission in transitioning plots (4703.33 01 5780.01 ug N (N2O) m-2 hr-1) were lower than long term no-till (5816.781 ug N (N2O) m-2 hr-1), organic (5780.01 ug N (N2O) m-2 hr-1) and conventional (7612.215780.01 ug N (N2O) m-2 hr-1) plots. Similarly, no-till in transition to organic was the most effective CH4 sink. It appears that a single first-time tillage generated disturbance carried out during the dry season does not lead to significant losses; however, subsequent wet season tilling may continue the accelerated mineralization leading to soil organic matter decline.