Model Description 1121 Concept

The SOMDY model presented here has been conceived to represent soil organic matter dynamics taking into account the following major issues:

- Improved definition of chemical composition of SOM

- Assessment of SOM physical structure

- Chemical and physical protection effects on mineralization processes

- Microbial turnover and chemical evolution of SOM during the decomposition

- Impact of agricultural practices on SOM dynamics

Then, the general structure and logic of SOMDY model is represented in Fig. 11.1. The model is modular and developed according to a system dynamic approach. It has been implemented by the Simile software (Muetzelfeldt and Massheder 2003) and it can be downloaded at http://www.ecoap.unina.it.

SOMDY is integrated with other models to handle environmental interactions and, specifically, water balance. This is done by interfacing Nasa Casa model (Potter et al. 1993) with water-dependent parameters in SOMDY. The initial requirements to run the integrated model are the definition of soil texture (% of sand, silt, and clay particles), bulk density, adsorbing mineral surface area, and the initial content and chemical composition of soil organic matter. Climatic data (min, max and average temperature, precipitation) are provided at run time by either hourly or daily time steps.

Fig. 11.1 Schematic representation of the logic behind the SOMDY model. Soil organic matter (SOM) is described in terms of its chemical composition (different spectral regions in solid-state 13C NMR spectra correspond to model layers) and physical structure of mineral/organic aggregation status (DOM dissolved organic matter; AOM aggregated organic matter). Mineralization produces CO2 emissions with rates depending on both chemical and physical characteristics (see text for details). Microbial turnover is accounted by the change in chemical composition during mineralization processes. The impact of agricultural practices (not shown in figure) is considered to affect liberation and degradation of larger-sized soil aggregates

Fig. 11.1 Schematic representation of the logic behind the SOMDY model. Soil organic matter (SOM) is described in terms of its chemical composition (different spectral regions in solid-state 13C NMR spectra correspond to model layers) and physical structure of mineral/organic aggregation status (DOM dissolved organic matter; AOM aggregated organic matter). Mineralization produces CO2 emissions with rates depending on both chemical and physical characteristics (see text for details). Microbial turnover is accounted by the change in chemical composition during mineralization processes. The impact of agricultural practices (not shown in figure) is considered to affect liberation and degradation of larger-sized soil aggregates

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