## 3 Results and Discussion
### Spray Deposition
#### 3.1.2 The Uniformity of the Deposition  
In addition to the total deposition, the uniformity of the deposition is also very important for controlling pests and diseases. The uniformity of the SPB sprayer was better than the others. The CV  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Spray Equipment**} & \multicolumn{2}{c}{**Total Deposition**} & \multicolumn{2}{c}{**Losses to the Ground**} & \multicolumn{2}{c}{**Recovery Rate**} \\  & **Avg. (\(\upmu\)g/Plan0 & CV (\%) & Avg. (\(\upmu\)g/cm\({}^{2}\)) & CV (\%) & Avg. (\%) \\ \hline UAV sprayer & 76.8 a & 87.2 & 0.13 b & 78.2 & 70.0 a \\ SPB sprayer & 68.7 a & 32.1 & 0.39 a & 39.0 & 62.7 a \\ EAP Sprayer & 84.8 a & 84.4 & 0.14 b & 118.2 & 77.3 a \\ KMB Sprayer & 61.9 a & 81.2 & 0.50 a & 97.1 & 56.5 a \\ \hline \end{tabular} Note: Values followed by the same letter in the column do not differ statistically (\(p<0.05\); Duncan’s Test).  
\end{table}
Table 1: The average (Avg.) and coefficient of variation (CV) of the total deposition on the plants, losses to the ground and the recovery rate of four sprayers.  
of the deposition was only 32.1%, which was significantly lower than the others (Table 1). This means it had a better deposition uniformity. However, the CVs of the deposition in this study was much greater than the value of Chinese National Standard requirement (10%) [27]. This may be due to the different measuring methods. In the study by [PERSON] et al. [28], the CV of the deposition distribution ranged from 5% to 10% with different spray pressures and nozzle heights, which are far lower than the result of our study. This is because the Teejet pattern check was used by [PERSON] et al., which is not influenced by the environment and the crop canopy. By comparison, the results in our study were a reflection of the actual uniformity of the deposition distribution on the crops.  
Compared with the SPB sprayer, the UAV sprayer had a significant lower uniformity of the deposition distribution with the CV of 87.2% (Table 1). This result was larger than the Civil Aviation of China General Aviation Operation Quality and Technology Standard for ultra-low volume spraying, which is 60% [8]. The uniformity of the deposition distribution of the UAV was influenced by many factors, such as the types [9], the flight accuracy, the flight parameters [7], the spraying system, the biased downwash wind [18] and the meteorological condition. Precise flight route control and auto navigation are essential for chemicals application with improving the deposition distribution uniformity [14]. [PERSON] et al. [8] developed an automatic navigation unmanned spraying system for the N-3 unmanned helicopter, which can significantly improve the deposition uniformity. The flight parameters also have a great influence on the deposition distribution uniformity. Various UAV sprayers under different flight parameters have been tested to find optimal spraying heights and speeds [7; 10; 18]. [PERSON] et al. [7] found that the flight parameters affect not only the distribution uniformity on rice canopy but also the control efficacy on wheat hoppers. [PERSON] and [PERSON] [29] pointed out that most agricultural helicopters exhibit biased downwash, resulting in an uneven spray pattern. To address this problem, a roll-balanced agricultural helicopters with an elevated-polyn tail rotor system was developed. In their study, the uniformity of the spray patterns and area of coverage was improved.  
The CVs of depositions of the EAP and KMB sprayer were 84.4% and 81.2%, respectively, which indicate a nonuniform deposition (Table 1), mainly due to the manual operation of the sprayer. The deposition uniformity was worse because it depended on the stability of the traveling speed along the spraying route and on the regularity of the arm movement of the operators.