Mineral fertilizers application is an agricultural task widely performed by centrifugal spreaders. These machines give satisfying results with regularly spaced parallel tractor trajectories but lead to over and under-applications when geometrical singularities occur (non-parallel paths, start and end of spreading,...). The application errors result then in watercourses pollution and important yield losses. In this study, in order to improve fertilizer application by centrifugal spreading, an optimization problem is considered. The optimal parameters are computed by taking into account the mechanical constraints of the machine so that they can be used as reference variables to control the spreader in the future. Faced with a large scale constrained problem, an augmented lagrangian algorithm using a l-bfgs technique is implemented. The improvements provided by this new method are exposed through simulation results for parallel and non parallel paths in the field.