## 4 Results and Discussion
### Field Experiment  
Since the flying height of the UAV influences the falling and final landing of the seeds to a large extent, before the formal field experiment, we performed a trial seeding test in which several mud boxes were placed on the ground to collect the seeds, and the seed landing effects of different flying heights were compared. Through the trial, the proper flying height was determined to be 1 m. Then, the formal field experiment of the aerial seeding operation process was conducted in the autonomous operation mode in which the working width was 2.1 m, the flying work speed was 4 m/s, the rotation speed of gear disc was 25 r/min, the seed layer height was 45 mm, and the wind pressure was 2450 Pa, which was compared to another two seeding modes. They used roughly equivalent seed quantity per hectare with the same kind of rape seed and field management.  
After seeding, further investigations were followed including counting the seed germination rate after 30 days, monitoring seedling growth situation in later months, and calculating yields and counting stubble after harvesting. The results of the yields and the crop stubble numbers by three different seeding systems are shown in Table 4. The average crop number per hectare \(N_{2}\) was estimated by proportionally enlarging the crop stubble number per square meter \(N_{1}\) and removing the gutter area by multiplying a coefficient of 0.9, that's \(N_{2}=N_{1}\times 10^{4}\times 0.9\).  
From the data in Table 4, we found that:  
1. The area of fields tested for three different systems were similar from 928.0 m\({}^{2}\) to 997.4 m\({}^{2}\) with corresponding yields of 135.15 kg to 168.3 kg.
2. Further calculations resulted in estimated average yields from 1192.13 to 1409.56 kg/hm\({}^{2}\), in which the first mode had a slightly superior performance (5.30% and 18.24% greater) to the other two modes. The yields of all three modes were lower than the normal value in general for this rape variety of Huayouza-62. This might be due to some uncertain common problems in the field management and the relatively low soil fertility of the original fields.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Seeding** & **Seeding System** & **Area (m\({}^{2}\))** & **Yield (kg)** & **Estimated** & **Crop Stubble** & **Estimated Average** & **Crop Number per** \\
**Mode No.** & & & & **(kg/hm\({}^{2}\))** & **Square Meter \(N_{1}\)** & **Hectare \(N_{2}\)** \\ \hline
1 & Aerial seeding & & & & & \\ system in this & 997.4 & 168.3 & 1409.56 & 46.0 \(\pm\) 7.2 & 4.19 \(\times\) 10\({}^{5}\)\(\times\) (1 \(\pm\) 14.1\%) \\ study & & & & & & \\ Aerial seeding & & & & & & \\ system in study & 986.0 & 165.9 & 1338.54 & 42.7 \(\pm\) 6.8 & 3.84 \(\times\) 10\({}^{5}\)\(\times\) (1 \(\pm\) 14.4\%) \\
13 & Ground planter & 928.0 & 135.15 & 1192.13 & 45.5 \(\pm\) 7.8 & 4.10 \(\times\) 10\({}^{5}\)\(\times\) (1 \(\pm\) 15.4\%) \\ (Weiye 2 BFG-4) & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Yield investigation and stubble counting results.  
3. Average crop numbers per hectare, which was estimated by converting the stubble number while removing the area of the drainage ditch, were equal within error and met the agronomic technical requirements of seedling number per hectare. The first mode had the highest value of crop number and the best average yield. The second mode had the smallest value but the second average yield. The third mode had the second value of crop number, but the worst average yield. Two factors might be the cause of the above results. One would be the counting errors and sampling spot differences. The other might be the differences in soil fertility between fields.