The effect of soil pH and dicyandiamide (DCD) on N2O emissions and ammonia oxidiser abundance in a stimulated grazed pasture soil

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.

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Determining nitrous oxide emissions from subsurface measurements in grazed pasture: A field trial of alternative technology

Soil Research ◽

10.1071/sr04106 ◽

2005 ◽

Vol 43 (6) ◽

pp. 677 ◽

Cited By ~ 15

Author(s):

Z. Li ◽

F. M. Kelliher

Keyword(s):

N2o Emission ◽

Gas Diffusion ◽

Nitrous Oxide Emissions ◽

Spatial And Temporal Variation ◽

Measurement Technology ◽

N2o Emissions ◽

Emission Measurement ◽

N2o Production ◽

Grazed Pasture ◽

Poorly Drained Soils

Beneath pasture grazed by farmed animals, the soil’s nitrogen (N), oxygen, and temperature regimes can be unevenly distributed in time and space. It is difficult to capture spatial and temporal variation of N2O using conventional emission measurement technology based on gas samples taken in chambers that briefly cover a small area of the soil’s surface. We report the results from field deployment of alternative, non-intrusive N2O emission measurement technology that uses subsurface measurements incorporating the soil processes controlling the net N2O production and gas diffusion rates. During 100 autumn and winter days after dairy cattle urine was applied (650 kg N/ha) to freely and poorly drained pastoral soils near Hamilton, New Zealand (37.8° S, 175.3° E), N2O emissions were determined. The measured values ranged from 0.024 to 1.55 and 0.048 to 3.33 mg N2O-N/m2.h for the freely and poorly drained soils, respectively. Over the 100 days, it was estimated that 0.4 and 1.3% of the applied N was directly emitted to the atmosphere as N2O from the freely and poorly drained soils, respectively.

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