SWORM: an agent‐based model to simulate the effect of earthworms on soil structure

Abstract

Soil structure can be defined as the spatial organization of solid mineral and organic particles, and pore space. It is of great importance for soil functioning as it drives ecosystem functions (carbon sequestration, emission of greenhouse gases, nutrient cycling, primary productivity, etc.). Soil structure results from biotic and abiotic factors. Among biotic factors, numerous studies have shown the importance of organic matter, microorganisms, roots and invertebrates. Earthworms are known to play a key role in soil structure formation and maintenance through a continuous production of biogenic structures (casts and burrows). As far as we know, no models describe or quantify the effect of soil invertebrates on soil aggregation and porosity. It is a challenge to describe the physical soil environment for purposes of modelling because a soil is a multi-scale heterogeneous, three-dimensional and dynamic environment. An approach based on fractal theory (often used in soil sciences) was chosen to model such a real complex environment; it was integrated into a multi-agent system (MAS), which allows us to simulate agents (e.g. earthworms) situated in a virtual world (e.g. soil). It is a bottom-up approach that allows us to describe a system at a micro level (e.g. earthworms and their local soil environment) in order to observe, during simulations, macroscopic changes (e.g. soil structure evolution, organic matter dynamics, and microbial functions). In this paper we describe the SWORM (for 'Simulated Worms') model and the simulator, and present the results of the simulation applied to a case study. The effect of compacting and decompacting earthworm species on the structure of humid savanna soil at Lamto in Coˆte d'Ivoire has been widely studied. Quantitative and graphical outputs (e.g. thin sections of the virtual soil) indicate that the simulator was able to reproduce the effects of both compacting and decompacting species. Different ways to improve the model are discussed.

Role of Soil Macrofauna in Phosphorus Cycling

“…Companion field studies should aim to better understand the volume of soil impacted and the dynamics of the biogenic structures produced, on a landscape scale. Coupled modeling approaches can also be useful to fully understand the complex interplay of biogeochemical interactions and to upscale from cast levels to soil profile and the entire ecosystem (Standing et al 2007;Blanchart et al 2009). …”

Cropping Systems to Improve Soil Biodiversity and Ecosystem Services: The Outlook and Lines of Research

“…Most ecological models have tended to focus on one functional group. For instance, the SWORM model describes the action of earthworms on soil structure through bioturbation and estimates the fate of soil organic matter and soil structure at soil profi le scale (Blanchart et al 2009 ). This model is being developed to give a better description of the interactions between earthworms and microorganisms in order to predict their impact on nutrient availability to plants and, consequently, on plant growth.…”

Introduce Collaboration in Methodologies of Modeling and Simulation of Complex Systems

“…In this context, a work (presented in [2], [3]) aims at reproducing the earthworms influence on the soil structure and the nutrient availability by simulation. For this purpose an agent-based model has been developed: Sworm.…”