Simulating greenhouse gas emissions and stocks of carbon and nitrogen in soil from a long-term no-till system in the North China Plain

Accurate modeling of tillage impacts on the cycling of soil carbon (C) and nitrogen (N) and greenhouse gas (GHG) emissions is complicated due to the differences in soil organic matter decomposition, water holding capacity and soil temperature between different tillage systems. In the current study, the SPACSYS (Soil-Plant-Atmosphere Continuum System), a process-based model, was used to simulate the effects of two different tillage regimes on crop yields, the dynamics of soil organic carbon (SOC) and total nitrogen (TN) stocks from 2003 to 2009, and soil CO2 and N2O emissions from 2003 to 2007. The study was based on a long-term tillage experiment with a winter wheat (Triticum Aestivium L.) and summer maize (Zea mays L.) system in Calcaric Fluvisols (FAO) soil in the North China Plain. Farmers' conventional tillage (CT), which is a predominant tillage method in the region, was used to compare with no-till (NT), an emerging technique for land conservation. In both treatments, chemical N fertilizer (F) was applied and crop straw (R) was incorporated in two field soils after harvest (no-till: NT-R-F; conventional tillage: CT-R-F). Statistical analyses indicated that the SPACSYS model reasonably simulated the maize yield under both NT-R-F and CT-R-F, but overestimated the wheat yield under NT-R-F by approximately 15%. In addition, the dynamics of SOC and TN stocks (0-10 cm soil depth) and soil CO2 and N2O emissions under both NT-R-F and CT-R-F were accurately simulated by the SPACSYS model. The simulations showed that NT-R-F significantly increased SOC and TN stocks at 0-10 cm soil depth, but not the wheat and maize yields compared to CT-R-F. Furthermore, NT-R-F reduced both soil CO2 and N2O emissions (P < .05) compared to CT-R-F. Our results also showed that NT-R-F led to greater C (3755 ± 942 kg C ha−1 yr−1) and N gains (179.8 ± 90.7 kg N ha−1 yr−1) in the plant and upper 20 cm depth of soil system than CT-R-F. In conclusion, the SPACSYS model can accurately simulate the processes of C and N cycles as affected by both conventional tillage and no-till systems in the North-China-Plain. Further studies need to focus on optimizing the rates of N fertilizer input and straw incorporation along with no-till to maintain the crop yield while reducing C and N losses to the environment.