Effects of residue removal and tillage on greenhouse gas emissions in continuous corn systems as simulated with RZWQM2.

Agricultural production is a major source of carbon dioxide (CO) and nitrous oxide (NO) globally. The effects of conservation practices on soil CO and NO emissions remain a high degree of uncertainty. In this study, soil CO and NO emissions under different residue and tillage practices in an irrigated, continuous corn system, were investigated using the Root Zone Water Quality Model (RZWQM2). Combinations of no/high stover removal (NR and HR, respectively) and no-till/conventional tillage (NT and CT, respectively) field experiments were tested over the four crop-years (Apr. 2011-Apr. 2015). The model was calibrated using the NRCT, and validated with other treatments. The simulation results showed that soil volumetric water content (VWC) in the NR treatments (i.e., NRCT and NRNT) was 1.3%-1.9% higher than that in the HR treatments (i.e., HRCT and HRNT) averaged across the four years. A higher amount of CO and NO emissions were simulated in the NRCT across the four years (annual average: 7034 kg C/ha/yr for CO and 3.8 kg N/ha/yr for NO), and lower emissions were in the HRNT (annual average: 6329 kg C/ha/yr and 3.7 kg N/ha/yr for NO). A long-term simulation (2001-2015) suggested that the CO and NO emissions were closely correlated with the stover removal degree (SRD), tillage, VWC, soil temperature (ST), years in management (Y), and fertilizer application. Stover and tillage practices had cumulative effects on CO emissions. The simulated annual CO emissions in 1st year from NRCT, NRNT, and HRCT were 7.8%, 0.0%, and 7.7% higher than that from HRNT, respectively; then the emissions in 15th year were 63.6%, 47.7%, and 29.1% higher, respectively. Meanwhile, there were no cumulative effects on NO emissions. The results also demonstrated that the RZWQM2 is a promising tool for evaluating the long-term effects of CO and NO emissions on different conservation practices.