As an essential part of field coverage path planning process, mobile agricultural field equipment headland turning is a process that should be done in a manner that can maximise the equipment’s operational efficiency through minimising the time or travel distance during the turning. However, this headland turning trajectory optimisation task represents a challenging dynamic nonlinear optimisation problem which is difficult to solve by using traditional indirect numerical methods. In this research, we investigated the possibility of using direct numerical methods to solve such a nonlinear optimisation problem in a restricted parameter neighborhood with constraints. We developed the kinematic models of the tractor and the tractor-implement(s) systems and formulated their headland turning optimisation problems through incorporating their models and the operational constraints. A range of headland turning scenarios from symmetrical bulb turn to fishtail turn and to turns with single and double trailers. With integration of the tractor and trailer models and by implementing the optimization process with the TOMLAB/SNOPT software tool, results for diverse circumstances of the tractor/trailer headland turning scenarios were generated and illustrated in this paper.