Carbon, Aggregate and Structure Turnover Model

The Carbon, aggregate and structure turnover model (CAST) (Stamati et al., 2013) was used in this study. The CAST model simulates the aggregation mechanism assuming three classes of aggregates:  the silt-clay sized aggregates (AC1, size less than 53 μm), the micro-aggregates (AC2, size 53-250 μm) and the macro-aggregates (AC3, size greater than 250 μm). In addition the model considers five carbon pools with distinct turnover rates: Decomposable Plant Material (DPM), Resistant Plant Material (RPM), Microbial Biomass (BIO), Humified Organic Matter (HUM) and Inert Organic Matter (IOM). The AC1 aggregate type contains BIO, HUM, and IOM. The AC2 aggregate type contains BIO, HUM, IOM, and fine DPM and RPM pools and the AC3 aggregate type contains BIO, HUM, IOM, and fine and coarse deriving DPM and RPM pools. Each carbon pool of the aggregate types decomposes by a first-order process with its own characteristic rate, in the same way as in the RothC model producing CO2, BIO and HUM, apart from the IOM pool which corresponds to biochar and is resistant to decomposition. The model assumes that macro-aggregates are formed around particulate organic matter (POM), followed by the formation of micro-aggregates (AC2) within the macro-aggregates. Plant residue colonized by microbial decomposers provides the binders for soil particles and small aggregates to form macro-aggregates (AC3) around POM. This POM is further decomposed and the fine fragmented POM is encrusted with silt-clay sized aggregates (AC1) leading to the formation of micro-aggregates within macro-aggregates (AC2 in AC3). Due to decrease of microbial activity, aggregate disruption occurs with instant release of stable AC2 and AC1 aggregates and POM becomes unprotected. When fresh plant residue enters the system, new aggregates form. The CAST model also simulates the effect of tilling and the impact of frozen ground on the aggregation/disaggregation mechanism in order to improve its versatility and improve the simulation of the dynamics of organic matter in the soil. 


Licence: Open source

Operating System(s): Windows

Modelled processes...


  • Apostolakis Α., S. Panakoulia, N P. Nikolaidis, N V. Paranychianakis, 2017. Shifts in soil structure and soil organic matter in a chronosequence of set-aside fields,  Soil & Tillage Research, 174, 113-119.
  • Panakoulia S.K., N.P. Nikolaidis, N.V. Paranychianakis, M. Menon, J. Schiefer, G.J. Lair, P. Kram, S.A. Banwart, 2017. Factors Controlling Soil Structure Dynamics and Carbon Sequestration Across Different Climatic and Lithological Conditions, In: Quantifying and Managing Soil Functions in Earth’s Critical Zone: Combining Experimentation and Mathematical Modelling, Advances in Agronomy volume 142 pp. 241-276 (edited by Donald L. Sparks and Steven A. Banwart). Elsevier, Amsterdam
  • Stamati F., N.P. Nikolaidis, S.A. Banwart and W.E. Blum, 2013. A Coupled Carbon, Aggregation, and Structure Turnover (CAST) Model for topsoils, GeoDerma, 211-212, pp51-64.