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Lianhai Wu, Rothamsted Research



The SPACSYS model (Wu et al., 2007) is a mixed dimensional, multi-layer, field scale, weather-driven and daily-time-step dynamic simulation model. Since it was published, more functions have been brought in (Bingham and Wu, 2011; Liu et al., 2013). The current version includes a plant growth and development component, a nitrogen cycling component, a carbon cycling component, a phosphorus cycling component, plus a soil water component that includes representation of water flow to field drains as well as downwards through the soil layers, together with a heat transfer component. All components are relatively independent each other, the linkage between components (information exchange) relies on ‘helper’ functions written within the components. The components themselves and linkages among the components are designed using object-oriented techniques and implemented in C++ with the component object model (COM). Inputs and outputs of all components are organised as a database in Microsoft® SQL Server 2005 or freeware MySQL. Root architecture is visualised by using the OpenGL graphics system.

The main processes concerning plant growth in the model are plant development, assimilation, respiration, and partitioning of photosynthate and nutrients from uptake estimated with various mechanisms implemented in the model, plus N fixation for legume plants, and root growth and development that is described in 3D root system by the following processes: branching, extension, architecture, mortality, water uptake and nutrient uptake. An alternative 1D root system is implemented to simplify processes involved in root growth and development. The functionality on water and nitrogen uptake by roots is also quantified.

Nitrogen cycling coupled with carbon cycling in the SPACSYS model covers the transformation processes for organic matter (OM) and inorganic N. The organic matter pool is further divided into fresh OM, dissolved OM, a litter pool as well as a humus pool, and inorganic N includes a nitrate pool and an ammonium pool. The main processes and transformations causing size changes to soluble N pools are mineralization, nitrification, denitrification and plant N uptake. Most of these are dependent on soil water content and temperature. Nitrate is transported through the soil profile and into field drains or deep groundwater with water movement. A biological-based component for the denitrification process has been implemented that can estimate nitrogen gaseous emissions.

The process-based phosphorus (P) cycling component is linked to other components, e.g. plant component, heat transformation and water cycle. The P pool for organic forms was subdivided into certain subpools with different forms and similar to soluble P. There are some connections among those sub-pools with chemical, physical and biological processes.

The Richards equation for water potential and Fourier’s equation for temperature are used to simulate water and heat fluxes, which are inherited from the SOIL model. Water in the soil profile is held mainly in the micro and meso pores of the soil matrix, but if the water content in a layer rises above a specified value a proportion is held in macropores from where rapid downward water (and solute) movement takes place due to gravitational forces alone. Water flow from the soil profile to a drainage pipe occurs when the ground water table is above the bottom level of the pipe and the soil below the ground water table is saturated. The Hooghoudt drainage flow equation with modification is adopted for the subsurface drainage flow.


Scientific articles

Wu, L., McGechan, M.B., McRoberts, N., Baddeley, J.A., Watson, C.A., 2007. SPACSYS: integration of a 3D root architecture component to carbon, nitrogen and water cycling - model description. Ecol. Model. 200, 343-359.

Bingham, I.J., Wu, L., 2011. Simulation of wheat growth using the 3D root architecture model SPACSYS: validation and sensitivity analysis. Eur. J. Agron. 34, 181-189.

Liu, Y., Wu, L., Watson, C.A., Baddeley, J.A., Pan, X., Zhang, L., 2013. Modeling Biological Dinitrogen Fixation of Field Pea with a Process-Based Simulation Model. Agron. J. 105, 670-678.


Technical information

Operating system(s): Windows

Output(s): detailed fluxes and state variables

Export format(s): stored in DBMS and can be exported to ASCII format

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