Parameter optimization and economic analysis of unmanned aerial vehicle (UAV) assisted liquid pollination for Kuerlexiangli pear

Abstract:【Objective】Kuerlexiangli pear is a characteristic fruit in Xinjiang, and is mainly planted in southern Xinjiang, with a planting area of 71 000 hectares, playing an important role in the local agricultural economy. Kuerlexiangli pear is a cross-pollinated fruit tree with many problems in pollination. The natural pollination depends on bees and other pollinating insects, whose activities are under the in- fluence of weather conditions and poorly controlled. The current artificial pollination method has some problems such as low efficiency, high cost and uneven pollination. UAV aided liquid pollination has the advantages of high efficiency, low cost and good pollination effect, and can well solve the  problems of pollination in Kuerlexiangli pear. In order to optimize the use of UAV aided liquid pollination technology in production, this study tried to select the best combination of technical parameters re- lated to UAV aided liquid pollination used in Kuerlexiangli and analyzed its economic profit. The pa- rameters included concentration of pollen suspended in pollination solution per unit area, pollen sus- pension dilution ratio and application time after pollen suspension preparation.【Methods】11-year-old Kuerlexiangli pear trees were used as the experimental materials. Pollen grains were collected from Yali (commercially provided by the Institute of Bee Research, Chinese Academy of Agricultural Sci- ences, collected by bees). The pollination solution consisted of 500 parts of water, 50 parts of white sugar and 1 part of pollen partner. A DJI T20 plant protection drone was used as the pollination de- vice, with a flying height of 2 meters above the top of the canopy. The spraying volume and moving speedofthedronewere1L per 666.7m2 and 4.5 m·s-1,2L per 666.7m2 and 4 m·s-1,or3Lper 666.7 m2 and 2.7 m · s- 1, respectively. Natural open pollination served as the control. The study exam- ined the effects of different pollen application dosages, different pollen concentrations, and different application time after preparation on fruit set in Kuerlexiangli pear, and compared the pollination costs between UAV aided liquid pollination and artificial pollination with dipping and shaking.【Results】When the 1∶500 pollen suspension was applied immediately after preparation, the inflorescence fruit setting rate and flower fruit setting rate were 63.44% and 17.74%, 87.72% and 30.70%, and 88.57% and 30.79% in spraying volumes of 1 L per 666.7 m2 (J1), L per 666.7 m2 (J2) and 3 L per 666.7 m2(J3), respectively, while in CK (natural pollination) fruit setting rate and flower fruit setting rate were 45.61% and 14.47%, respectively. The fruit setting rate in J3 and J2 was significantly higher than that in J1 and CK. When pollen suspension application volume was 3 L per 666.7 m2 and pollen suspen- sion was spayed immediately after preparation, the inflorescence fruit setting rate and flower fruit set- ting rate were 80.56% and 23.61%, 80.00% and 23.33%, 61.76% and 14.71%, and 49.17% and 14.58% in treatments with 1∶250 (B1), 1∶500 (B2), 1∶750 (B3) and 1∶1000 (B4) pollen suspensions, respectively. Fruit setting rate in B1 and B2 was significantly higher than in B3, B4 and CK. When spraying volume was 3 L per 666.7 m2 and the pollen concentration was 1∶500, the inflorescence fruit setting rate and flower fruit setting rate were 75.83% and 19.72%, 75.76% and 19.19%, and 64.71% and 17.16% in treatments with pollen suspension sprayed at 0 h (S1), 0.5 h (S2) and 1 h (S3) after preparation, respectively. Fruit setting rate in S1 and S2 was significantly higher than in S3 and CK. Under a spray volume of 3 L per 666.7 m2 and pollen concentration of 1∶500, the pollination cost was 82 yuan per 666.7 m2, while the cost of artificial pollination was 240 yuan per 666.7 m2 and 390 yuan per 666.7 m2 for dipping and shaking pollination, respectively. The UAV aided liquid pollination saved 158-308 yuan per 666.7 m2 compared with the two traditional artificial pollination methods【. Conclu- sion】The optimal combination of technical parameters for UAV assisted liquid pollination used in Kuerlexiangli pear was: spraying volume of 3 L per 666.7 m2, pollen concentration of 1∶500, and immediate spray after preparation. This combination generated a inflorescence fruit-setting rate and a flower fruitsetting rate of 88.57% and 30.79%, respectively, and significantly saved cost.