Conceptual Modelling of the Dynamics of Soil Macroporosity Based on an in Situ and Direct Observation of Major Soil Structuring Agents During Early Stage of Pedogenesis

Many factors affect soil porosity but major of them are soil fauna, plant roots and the climate. Many studies attempted to investigate the effect of these factors on the evolution of soil porosity separately. The objective of this study is, based on an in situ experiment including three major porosity factors, propose a conceptual model of soil macroporosity evolution. In situ observation and quantification of the evolution of macroporosity under the influence of each agent separately and the three agents combined allow to propose a model for each case. Results show that the evolution of macroporosity due to plant roots is linear and reachs its maximum at the end of the plant cycle. Earthworms create and destruct macroporosity during the up and down movement for food searching. At long term, the consequence of earthworm action results to an increase of macroporosity. Wetting and drying cycle has the same effect as earthworm. At the beginning, when soil shrinks, it leads to a creation of macroporosity that could be disturbed by swelling during soil humectation. Some soil particles migrate in the shrink and reduce the surface of macroporosity. When faced to many wetting drying cycles, the surface of macropores increase during time. Mathematical algorithms and computing are necessary to formalize this model and long-term experiment is needed to validate it.