Modelling Lumbricus terrestris population dynamics in agricultural fields.<br />Contribution to the study of cropping system impacts on earthworm communities.

Earthworms, which represent a major component of soil macrofauna, are often presented as biodiversity and soil quality indicators. Moreover, they are deemed to be ecosystem engineers since they directly or indirectly impact the availability of resources to other species as plants and microorganisms. Earthworms play a central role in the ecological functioning of agroecosystems thanks to their contribution to processes influencing physical, chemical and biological soil components.<br />This work is aimed at understanding and modelling earthworm population dynamics in cultivated fields and to study the impact of cropping systems on earthworm communities. Our model, WORMDYN, is a stochastic stage-based Lefkovitch matrix model which accounts for vertical migrations and predicts Lumbricus terrestris dynamics in ploughed and superficially tilled plots (Grignon, France). In the model, the earthworm population is divided into four developmental stages (cocoons, juveniles, sub-adults, and adults) and life cycle parameters depend on soil temperature and water content which are the main factors influencing L. terrestris short-term dynamics. The model parameters were estimated from the available literature.<br /> This study of L. terrestris population dynamics entailed many samplings in cultivated fields. However, various methods are classically used for earthworm samplings. We thus wanted to determine the most suitable earthworm sampling method, combining efficiency and manipulator safety. The first part of this work thus presents the comparison of three chemical expellants for earthworm sampling.<br />Then, WORMDYN structure is presented, as well as the comparison between model outputs and experimental data. A sensitivity analysis was carried out to identify the parameters which should be estimated with a higher precision in order to improve the predictive capabilities of the model.<br />Finally, to assess the impact of cropping systems on earthworm communities, data were collected in a long-term trial including three cropping systems: a conventional system, a "Direct seeding living Mulch-based Cropping system" and an organic system without fertilisation. Results were used to study WORMDYN behaviour in these situations and to get information to improve model performance.