Quoted from: Gilhespy, Sarah L., Steven Anthony, Laura Cardenas, David Chadwick, Agustin del Prado, Changsheng Li, Thomas Misselbrook et al. "First 20 years of DNDC (DeNitrification DeComposition): model evolution." Ecological modelling 292 (2014): 51-62. https://doi.org/10.1016/j.ecolmodel.2014.09.004 

The DNDC model was first described by Li et al. (1992). The first versions (1.0 – 7.0) of DNDC consisted of three main sub models (Fig. 2) which worked together in simulating N2O and N2 emissions; (1) soil-climate/thermal-hydraulic flux sub-model, (2) decomposition sub-model, and (3) denitrification sub-model.

 

Fig. 2. The structure of the early version of the DNDC model incorporating three submodels (taken from Li et al., 1992).

During the following two decades many improvements and additions were added to the early version of the DNDC model. In 1994, the model was supplemented with an empirical plant growth sub-model (Li et al., 1994) which contained sub-routines for land cropping practice routines/land management to study the biogeochemistry of soil C in arable land. Later, the DNDC model formed the basis of a new forest model (Section 3.1.2) named PnET-N-DNDC (Li et al., 2000), and many of the developments that were made in producing PnET-N-DNDC were also incorporated into the DNDC model (Li, 2000), as was the case with many of the stand-alone versions of DNDC that were developed over time.

The DNDC model was further developed to predict methane (CH4) and ammonia (NH3) emissions from agricultural ecosystems. Li (2000) explained that in order to construct a process model of soil trace gases, all the factors including ecological drivers, soil environmental variables, and biogeochemical reactions should be integrated into one framework. To this end, Li (2000) adopted the concept of a biogeochemical field, ‘a biogeochemical field is an assembly of the spatially and temporally differentiated environmental forces (e.g., temperature, moisture, pH, Eh and substrate concentration gradient) that drive biogeochemical reactions in an ecosystem’. The model was reorganised into two components incorporating six sub-models (Fig. 3) and this new structure formed the basis of many DNDC-based models (Table 1). Component 1 linked ecological drivers to soil environmental variables and consisted of the soil climate, crop growth and decomposition sub-models. Component 2 linked soil environmental factors to trace gases and consisted of the already known denitrification sub-model and furthermore, the two new sub-models for nitrification and fermentation.

 

Fig. 3. The two-component DNDC model with six submodels: soil climate, crop growth, decomposition, denitrification, nitrification and fermentation (taken from Li, 2000).

The DNDC model (Li, 2000) was further modified by adding several key crop algorithms which were developed as part of Crop-DNDC (Section 3.1.3) to produce a phenological crop growth sub-model. During the development of Wetland-DNDC (Section 3.1.4), Li et al. (2004a) and Li (2007) further developed the concept of the ‘anaerobic balloon’ that was first introduced in PnET-N-DNDC by merging the Nernst and Michaelis–Menten equations, to form the core of DNDC (DNDC v. 8.5, Table 1), this being possible due to both equations sharing a common factor (oxidant concentration), to track microbial activities.

In more recent years DNDC has formed the basic structure of increasingly more complex modular-based models such as Mobile-DNDC and Landscape-DNDC (Table 1). There are also a number of models that have been developed for different regions of the world, e.g. NZ-DNDC, UK-DNDC, and specific crops, e.g. DNDC-Rice, DNDC-SCW (Table 1). At the same time, many further improvements have been added to the DNDC model itself. In Li et al. (2006), further enhancements were introduced to improve the model capacity for simulating free NH4+ dynamics, nitrification, and NO3− leaching. A function as described by Steiner (1989) was added to the DNDC model to improve estimates of soil evaporation under different levels of surface residue cover. Recent versions of DNDC share the same soil NH3 algorithms as Manure-DNDC (Section 3.1.17), described in detail by Li et al. (2012). DNDC has also been improved in simulations of crop growth, and alternative farming management practices such as the use of nitrification inhibitors, slow-release fertilizers, sprinkler and drip irrigation, plastic film mulching etc. to meet the demand for GHG mitigation studies. Two basic hydrological features were added to DNDC to enhance its capacity for modelling surface runoff and soil erosion (Deng et al., 2011). At the date of writing this paper (June 2014), the latest version of DNDC is 9.5.