LAUSR

The feasibility of aerial fertilization by UAV-based granular fertilizer spreaders (GFSs) has been widely accepted. Although commercial UAV-based spreaders have emerged, their performance in granular fertilizer spreading application has rarely been studied. This paper tested the performances of four existing UAV-based GFSs in the automatic controllability, range of the discharge rate and the swath width and uniformity of the distribution. An analytic hierarchy process (AHP)-based method was proposed to evaluate their comprehensive performance in spreading application. The main results are as follows: (a) GFS-A showed the maximum controllable discharge rate of 27 kg/min, and GFS-B showed the minimum (proximately 3 kg/min). The discharge rate could be changed in a stepless way by GFS-B, C and D. The relationship between the discharge rate and the rotational speed of the fluted roller of GFS-D showed a significant linear relationship ( $\text {R}^{2} = 0.9991$ ) for the operational range. (b) The distribution patterns of GFS-A and D were trapezoidal, which was the better deposition pattern for generating uniform spreading; those of the other two UAV-based GFSs were a wide triangle with obviously asymmetrical sides (GFS-B) and a typical M-shape with two peaks (GFS-C). (c) the simulation of CV-swath width illustrated that the available effective swath width (CV ≤ 20%) for these UAV-GFSs were 5.1m (CV = 14.73%), 4.8m(CV = 17.55%), 3.9m(CV = 13.02%) and 5.7m(CV = 18.36%) respectively under the given conditions. Furthermore, according to the AHP-based evaluation model, it was proved that GFS-D was able to provide superior performance in precise fertilization for a large application range, which is important for its practical application. This comparative study makes useful contribution for farmers and researchers in this field in understanding the application performance of various UAV-based GFSs.