Effects of fertilization and stand age on N<sub>2</sub>O and NO emissions from tea plantations: A site-scale study in a subtropical region using a modified biogeochemical model

Abstract

Abstract. To meet increasing demands, tea plantations are rapidly expanding in China. Although the emissions of nitrous oxide (N2O) and nitric oxide (NO) from tea plantations may be substantially influenced by soil pH reduction and intensive nitrogen fertilization, process model-based studies on this issue are still rare. In this study, the process-oriented biogeochemical model, Catchment Nutrient Management Model – DeNitrification-DeComposition (CNMM-DNDC), was modified by adding tea growth-related processes that may induce a soil pH reduction. Using a dataset for intensively managed tea plantations at a subtropical site, the performances of the original and modified models for simulating the emissions of both gases subject to different fertilization alternatives and stand ages were evaluated. Compared with the observations in early stage of a tea plantation, the original and modified models showed comparable performances for simulating the daily gas fluxes (with Nash-Sutcliffe index (NSI) of 0.10 versus 0.18 for N2O and 0.32 versus 0.33 for NO), annual emissions (with NSI of 0.81 versus 0.94 for N2O and 0.92 versus 0.94 for NO) and annual direct emission factors (EFds). The observations and simulations consistently demonstrated that short-term replacement of urea with oilcake stimulated N2O emissions by ~ 62 % and ~ 36 % and mitigated NO emissions by ~ 25 % and ~ 14 %, respectively. The model simulations resulted in a positive dependence of EFd of either gas against nitrogen doses, implicating the importance of model-based quantification of this key parameter for inventory. In addition, the modified model with pH-related scientific processes showed overall inhibitory effects on the gases emissions in the mid to later stages during a full tea lifetime. In conclusion, the modified CNMM-DNDC exhibits the potential for quantifying N2O and NO emissions from tea plantations under various conditions. Nevertheless, wider validation is still required for simulation of long-term soil pH variations and emissions of both gases from tea plantations.

Update of a biogeochemical model with process-based algorithms to predict ammonia volatilization from fertilized cultivated uplands and rice paddy fields

“…Based on comprehensive observations, the CNMM-DNDC was initially tested in a subtropical catchment, which showed credible performances in simulating the yields of crops, emissions of greenhouse gases (i.e., methane and nitrous oxide), emissions of nitrogenous pollutant gases (i.e., nitric oxide and NH 3 ), and hydrological nitrogen losses by leaching and NO − 3 discharge in streams for different land uses (including forests and arable lands cultivated with maize, wheat, oil rape, or rice paddy) (Zhang et al, 2018). Subsequently, Zhang et al (2020) modified the CNMM-DNDC by adding tea-growth-related processes that may induce a soil pH reduction, and this modified model performed well in simulating the emissions of nitrous oxide and nitric oxide from a subtropical tea plantation plot. Moreover, the CNMM-DNDC performed well in simulating the NO − 3 leaching process of black soils in northeastern China (Zhang et al, 2021).…”

“…The Catchment Nutrient Management Model-DeNitrification-DeComposition (CNMM-DNDC) model, established by coupling the core carbon and nitrogen biogeochemical processes of DNDC (e.g., decomposition, nitrification, denitrification, and fermentation) to the distributed hydrologic framework of CNMM, is one of the latest versions of DNDC (Zhang et al, 2018). The CNMM-DNDC has been gradually developing into a comprehensive and reliable process-oriented biogeochemical model that performs well in terms of simulating the complex hydrologic and biogeochemical processes of a subtropical catchment with various landscapes (Zhang et al, 2018), the nitrous oxide and nitric oxide emissions from a subtropical tea plantation (Zhang et al, 2020), and the NO − 3 leaching processes of black soils in northeastern China (Zhang et al, 2021). However, the rationality of the CNMM-DNDC's scientific processes in simulating NH 3 volatilization from fertilized croplands is still lacking in terms of a thorough assessment.…”