| Variable-rate fertilization plays an important role in precision agriculture.Variable-rate spraying technology of UAV(Unmanned Aerial Vehicle)is not yet advanced,and its application in supplementing leaf liquid fertilizer is relatively poor.Based on low-altitude remote sensing information acquisition technology and aiming at achieving the goal of variable-rate fertilization technology for Rapeseed,based on multi-rotor UAV,this paper studied five main technical links of variable-rate fertilization,including canopy information acquisition,information processing,decision making analysis,UAV selection and parameter optimization,variable-rate spraying and evaluation.The main results were achieved as follows:(1)This paper studied the physical properties of the blade surface and the spray liquid and the interaction between them.Scanning electron microscopy(SEM)showed that the stomatal density on the opposite side of the leaf was about 1.5 times higher than that on the front side,which was more conducive to the effect of foliar fertilizer.It was an important evaluating indicator in practical operation.Orthogonal test and single factor test were applied to analyze the change of contact angle,which was affected by the location of leaf,foliar fertilizer type and concentration,adjuvants concentration,droplet size and velocity.The results showed that the most important factor affecting the performance of liquid wetting blades was whether to add additives.According to the test,the recommended concentration range of vegetable oil additives was 4‰~1%.In practical operation,the nozzles with higher initial velocity of spraying droplets and operating parameters should be selected as far as possible,so that the speed of droplets when it touches the blades was higher than 1.55 m/s,so as to achieve the best wettability of the droplet.(2)The integrated experiment of nitrogen diagnosis was carried out,and an innovative algorithm for generating prescription map was proposed..The RGB and multi-spectral images obtained by UAV remote sensing platform were used to predict canopy nitrogen at bolting stages of rape,and the determination coefficient R~2=0.88.After gray processing,extraction of operation area and determination of variable operation accuracy,the requirement of fertilizer was determined.After coordinate transformation,the processing of navigation position information was greatly reduced,and the variable response time of the whole automatic variable-rate control system was less than 200 ms.(3)The airborne spraying device was designed,and the eight-rotor UAV developed independently by the Institute of Agricultural Information Technology of Zhejiang University was adopted.The Arduino UNO R3 controller adopted PWM(Pulse Width Modulation)technology to control the variable speed of the diaphragm brushless water pump.In comparison with the droplet size,spatial distribution,velocity and spray wettability,IDK12002 air-injection nozzle was selected as practical nozzle in the field.The volume median diameter of the droplets from the IDK12002 nozzle was about 250 um,suitable for larger droplet fertilization spraying operation,the anti-drift performance of IDK12002 was good.(4)The eight-rotor automatic variable-rate spraying UAV carried out variable-rate spraying and evaluation analysis of its operation effect.Water sensitive papers image analysis software named"Droplet Analysis",which was suitable for plant protection UAV spraying,was developed.The results of several spray evaluation parameters were compared.The results showed that there was good deposition on the opposite side of the leaf of the canopy or bottom,which was due to the good penetration ability of IDK12002.The maximum error of variable-rate control was 1.75%compared with the actual amount and the setting amount.It can be basically determined that the eight-rotor automatic variable-rate spraying plant protection UAV designed in this study can realize the independent variable-rate spraying operation and meet the needs of precision agriculture. |
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