Mechanisation of ring-furrow fertiliser application for orchards: A multi-segment arc trajectory and its control method

Ring-furrow fertiliser placement is a precise near-root application method for orchards. However, it is still unclear what kind of fertiliser application trajectory is more conducive to precise near-root fertiliser placement and smooth mechanical operation and by what means it can be precisely controlled. Therefore, this study proposed a fertiliser application method based on a multi-segment arc trajectory that was evaluated by the accuracy of near-root fertiliser placement, and a root pruning coefficient. A control model for the transverse motion of the furrow opener was constructed and a novel method of segmental proportional-integral-derivative (PID) control was adopted to control the electro-hydraulic system for the ring-furrow trajectory. The results indicated that the multi-segment arc trajectory had outstanding advantages, with a smooth furrowing speed without abrupt changes, a fertiliser-root contact coefficient more than 1.5 times that of the traditional straight furrow trajectory, and a root pruning coefficient not exceeding 8.13 %. Field tests showed that the correlation coefficients between actual and target displacement curves of the furrow opener's transverse telescopic motion were >0.99, with the root mean square error (RMSE) of 0.010 m and 0.011 m, respectively, for the plant spacing of 1.3 m and 2.3 m. The control system enabled precise control of the multi-segment arc trajectory for accurate near-root fertiliser placement with smooth mechanical operation and good adaptability to plant spacings and heavy-load conditions. The study laid a theoretical foundation for developing mechanised ring-furrow fertiliser application technology in orchards.