| In recent years,the aerial control of plant pests has being developed rapidly in China.Currently,there are more than 20,000 plant protection aircrafts in China.And the percentage of plant protection drones(UAV)is over 95%.The DJi eight-rotor MG-1s plant protection UAV with four XR11001 VS nozzles was used to assess the influence of environmental variables such as temperature,wind speed,vegetation type as well as operational variables such as flight height on spraying parameters.The key factors of aerial control application was well studied in the present thesis.The monitoring of droplets in the operation of DJi UAV for plant protection is accomplished through the chromogenic reaction of water-sensitive papers.According to the environmental factors and operational variables,the water-sensitive papers were set up to monitor the spatial distribution of droplets under different operational conditions.According to analyses of drop density,effective spraying range,drop particle size,and drift distance,the influence of environmental variables and operational variables of the UAV for plant protection was finally determined.A field trial of UAV was carried out to control the aphids on red leaf plum trees,and the control efficiency and spatial distribution of droplets were further studied.The results showed that application height of the plant protection UAV posed a direct impact on the drop density,effective spray range and drop particle size.The effective spray range of the UAV is closely related to the operation height.The effective spray range of UAV operation increased with the increase of operating height.The effective spray range reached the maximum value of 6.7m at the operation height of 5.9m,and then decreased with continuesly increased operation height.The effective spray range droped to 3.9m at the height of 9.8m.Based on analysis of the two indexes of droplet variation coefficient(CV value)and droplet volume median diameter(VMD),the CV value of droplet gradually decreased with the increase of operation height.The decreased CV value represented more stability of droplet dispersion.The CV value was 0.2567 at 2.9m,and decreased to 0.1408 at the 5.9m.The lower CV value reprsented higher stability of droplets spatial distributiion.DV0.5 of droplets is the value that best reflects the drop particle size distribution in an aerial spray.With the increase of operating height,the average VMD value within the effective range showed a different trend with the creased height.When the operating height was below 4.1m,the average VMD value decreased slowly with the increase of operating height.When the operating height was between 4.1-7.2m,the increased height rapidly reduced the average VMD value of droplets.The VMD value tended to a stable value of 110 μm when operating height reached 7.2m or above.The relative humidity(RH)of the environment had a direct effect on the droplet deposition.At the operation height of 6m,the effective spraying range reached 6.8m at RH85%,and droped to 2.3m when the relative humidity decreased to 35%.The small droplets(<175 μm)whithin effective spray range ocuppied a percentage of 84.4% at RH85%,and droped to 62.9% at RH35%.The results showed that the dry airflow obviously accelerated the evaporation of droplets in the falling process of a aerial spay if the relative humidity was low,by which finally affected the deposition of fog drops,effective spray range as well as the proportion of different droplets sizes.When the operating height reached 9.8m,the effective spray range was only 3.9m at RH85%,and the proportion of small droplets decreased to 61.5%.Both the low environment RH and the hihg earial operation height enhanced the evaporation effect on the droplets,and the superposition of the RH and height accelerated the evaporation process.The drop drift was significantly positively correlated with the lateral wind speed intensity.When the lateral wind speed reached 0.6m/s,the drifting distance of droplets was 1.75 m.When the wind speed reached 2.3m/s,the drift distance increased to 3.35 m.Droplets with small particle size were more easily moved by the drift,which reduced the proportion of small droplets from 69.8% to 40.2% in the effective spray range when the lateral wind speed increased from 0.1m/s to 2.3m/s.The droplet drift increased droplet dispersal,but couldn’t increase the effective spray range.The UAV for plant protection showed a good penetration for both woody plants and herbaceous plants.A large number of droplets penetrated through the canopy of osmanthus fragrans to the bottom leaf or to various parts of the sage grass.The drop deposition on the bottom leaf of osmanthus fragrans was 63.51% of that on the top leaf,and the drop density on the bottom leaf also reached 71.10% of that on the top leaf.The drop penetration on herbacetes was even better.The density of drops in different parts on the down-side of leaves was very close,and the fluctuation ranged 213.90-227.66 drop/cm2,which was 42.47% higher than that of the up-side of the leaves.The deposition amount of fog droplets on the up-side leaves was larger than that on the down-side leaves.The deposition on leaf tip was higher than that of leaf bottom.The downforce wind and air turbulence generated by the UAV contributed the attachment of fog droplets,especially those of small particle size,to the lower layer of the canopy and the down-side of the leaves.The 6% plant-originatied pesticide Rotenone emulsion with 400 times diluention was sprayed at a low dosage by the DJi UAV to control of peach aphids on red plums in a field trial.The results showed that the drop density on the up-side of leaf was significantly higher than that on the down-side of leaf no matter in the upper or lower layer of canopy.The drop densities on the up-side leaves both in upper and lower layers were 72.21 /cm2 and 129.42 /cm2,respectively,which were significantly higher than the density of 25.36 /cm2 and 46.45 /cm2 on the down-side of leaves.The aerial control by the UAV got a good control.The corrected control effect of aphids in the upper layer and the lower layer was 83.8% and 95.1%,respectively,on the 7th day of control..The reason for the better control of the aphid in the lower layer was because that the drop density on the down-side of leaves in the lower layer was 1.83 times than that of the up-side.In general,the environmental temperature,relative humidity,wind speed,plant type as well as the height of flight operation are closely related to the drop spatial distribution,effective spray range,droplet deposition amount and drop density in a UAV aerial control,which need to be carefully considered before application of UAV control to ensure a good field control. |
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