## 3 Results and Discussion
### Working Efficiency  
Working efficiency is also an important evaluation index for equipment selection. The UAV sprayer used in the test belongs to semi-autonomous control, which is the most common in China. By recording the spraying time of five sorties with the filled tank, the average spraying time of each sortie of the UAV sprayer was calculated as 0.095 h (Table 2). The average spraying area of each sortie was 0.39 ha with the spray volume of 5 L (Table 2). Calculated from the spraying time and area, the work efficiency of the UAV sprayer was 4.11 ha/h (Table 2). The work efficiency test results were consistent with [PERSON] et al. [9], who reported that the working efficiency of UAV was at 13.4-18.0 hectare per 8 h, i.e., 1.68-2.25 ha/h. In his test, the operation items included the time of preparation, route planning, failure maintenance, and ground service, which accounted for 50% of the whole process. With micro-electronic technology development, the multi-sensor data fusion and real-time kinematic positioning technology and product will be applied in agriculture UAV, with which the UAV can achieve fully autonomous flight, significantly improving the working efficiency [41].  
Compared with the UAV sprayer, the SPB sprayer had a relatively lower working efficiency. The average spraying time was 0.39 h and the spraying area was 0.93 ha with the tank capacity of 280 L (Table 2). Although there are many other kinds of boom sprayers with a much longer boom, the complexity of the terrain and the farm size limit the usage of larger boom sprayers in China. The average farm size in China is amongst the smallest in the world of 0.67 ha and more than half (57.5%) of farms are small (<2 ha) [1]. Thus, this kind of small boom sprayer is widespread with the working efficacy of 2.38 ha/h (Table 2).  
From the test results, the working efficiency of two conventional knapsack sprayers were 1.57 and 0.21 ha/h, respectively (Table 2). Conventional knapsack sprayers need to be carried on the back, which easily leads to exhausting and lower work efficiency. Especially for the EAP sprayer, the working efficacy was only 5.1% of the UAV sprayer. Although these knapsack sprayers also hold very large market share (88%, from China Agriculture Yearbook Editorial Committee 2016) in China, with the development of technology and the growth of farming size, these lower working efficiency sprayers will be tapered and the studies on high efficiency sprayers will be necessary.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sprayer** & **Tank Capacity (L)** & \begin{tabular}{c} **Spray Area (Means \(\pm\)** \\ **Standard Error, ha)** \\ \end{tabular} & \
\begin{tabular}{c} **Spray Time (Means \(\pm\)** \\ **Standard Error, h)** \\ \end{tabular} &
\begin{tabular}{c} **Working** \\ **Efficiency (ha/h)** \\ \end{tabular} \\ \hline UAV sprayer & 5 & 0.39 \(\pm\) 0.04 & 0.095 \(\pm\) 0.01 & 4.11 \\ SPB sprayer & 280 & 0.93 \(\pm\) 0.06 & 0.39 \(\pm\) 0.03 & 2.38 \\ KMB Sprayer & 18 & 0.22 \(\pm\) 0.02 & 0.14 \(\pm\) 0.01 & 1.57 \\ EAP Sprayer & 16 & 0.039 \(\pm\) 0.004 & 0.19 \(\pm\) 0.01 & 0.21 \\ \hline \hline \end{tabular} Note: Spray area in the table means the area per spray with full tank. Spray time in the table means the time per spray with full tank.  
\end{table}
Table 2: Working efficiency (ha/h) of four sprayers.