| China is a large agricultural country,feeding 22%of the world’s population with 7%of the world’s arable land area.Fertilization and spraying are important links of the agricultural production process.Fertilizers can promote the growth of plants,and pesticides can control crop diseases,insects,and weeds.Efficient fertilization and spraying are not only beneficial to the growth of crops,achieving high agricultural yields and improving agricultural productivity,but also protects the soil and the environment,achieving rational use of resources and sustainable development of agriculture.At present,the fertilization and spraying machines developed at home and abroad are mostly single-functional and mainly for large field operations.There are few small fertilizing and spraying machines suitable for hilly and mountainous areas,and there are problems such as high labour intensity and serious waste of fertilizer and liquid in hilly mountainous areas.Therefore,it is of great significance to develop a fertilization and spraying machine suitable for hills and mountains.This paper combines the agronomic requirements of plants grown in hilly mountainous areas with discrete elements,sensors and automatic control technology to develop a small fertilization and spraying integrated machine for the above problems.The main research contents and conclusions are as follows:(1)Overall design of the machine and key componentsCombined with the agronomic requirements of fertilization and spraying,the whole machine design scheme of a small fertilization and spraying integrated machine was determined,and the key components such as the fertilizer spreading disc,the fertilizer amount adjustment device,the two-way adjustable spraying device,and the water/fertilizer tank were designed.The kinematics and dynamics of the fertilizer particles were analyzed,the dynamic equation of the fertilizer granules was obtained,and the range of working parameters affecting the fertilization uniformity was determined:the opening of the fertilizer opening is 40-80%,the fertilization height was 400～600mm,and the disc speed was 120～180r/min.Based on the analysis of droplet movement characteristics,the droplet coverage area control theory was determined.(2)Simulation experiment and parameter optimization of discrete element fertilization based on EDEMA simulation model of fertilizer particles was established by measuring the triaxial dimensions,angle of repose,moisture content,density and other physical characteristics of fertilizer particles;a virtual simulation test of the fertilizer application process was designed based on the 3D boundary model of the simplified device imported from Slid Works and combined with EDEM discrete element simulation analysis software;the test was conducted with the opening of the fertilizer drop opening,fertilizer spreading height and disc speed as test factors,and the coefficient of variation of the uniformity of fertilizer particles as test indicators.Based on the Box-Behnken experimental design theory,a quadratic regression orthogonal rotational combination simulation test was conducted to establish the regression model between the test factors and the indicators,and response surface analysis and parameter optimisation were carried out with the aid of Design-expert10 software.The results of the simulation tests show that the order of the coefficient of variation Cv affecting the uniformity is the rotation speed of the disc C,the opening of the fertilizer opening A,and the height of the fertilizer spreading B.After optimising the parameters,it can be seen that when the opening of the fertiliser drop opening is 62.63%,the spreading height is 482.97mm and the disc speed is 172.95r/min,the coefficient of variation of uniformity of fertilizer particle distribution(8.99%)is the smallest.At this point the uniformity of fertilizer spreading is the best and the spreading performance is the best.(3)Control system hardware and software designThe hardware system platform of fertilization and variable spraying with STM32F103ZET6 core controller was built,and the Altium Designer software was used to complete the design and construction of functional modules such as power supply stabilization,DC motor drive,forward speed detection,stepper motor drive,pump drive and human-machine interaction module.The system can obtain,calculate and process information such as forward speed and preset spraying volume in real time through sensors and the STM32 core controller,and drive DC motors,stepper motors and water pumps to act according to predetermined targets,assisting people to complete agricultural production.Applying the principle of modular programming,using C language as the system development language,using Keil u Vision 5 as the development environment and compiling and debugging tools,and the relevant functional modules of the hardware circuit are configured for the development of the software program;the design and development of the variable spraying system mainly focuses on the dosing of fertilization and the sub-programs based on user settings,speed detection,stepper motor and pump drive as well as sound and light alarm;PID feedback control is added to form a closed-loop control loop to further improve the control accuracy of the system,so that the software and hardware are combined with each other to jointly complete the operational execution of the machine series process.(4)Experimental study on the performance of fertilization and spraying of the whole machineThe prototype of the vehicle-mounted fertilization and spraying integrated machine was completed,and performance tests related to fertilization and spraying were carried out based on the prototype.The fertilization performance tests show that the mean value of the coefficient of variation of fertilizer particle distribution uniformity Cv is 9.72%under the optimal fertilization simulation parameters,and the average relative error compared with the simulation test is 7.36%,indicating that the simulation optimisation model is reliable and verifying the feasibility of the discrete element simulation;The test calibration of fertilizer drop opening and fertilizer discharge was carried out,and the linear correlation coefficient of determination between the two is R~2=0.9909,which can be used to guide agricultural production.The spraying performance tests show that:the variable spraying system has stable operational performance and can adjust the spraying volume according to the operating speed,and the average error between the target spraying volume set by the system and the actual spraying volume is 5.02%;In the horizontal mode,when the PWM duty cycle is 40%～100%,the spraying volume of the nozzle ranges from 74.94～345.41m L/min,and the coefficient of variation of the nozzle uniformity is less than 5%;Under the optimal spraying parameters,the spraying width and range of the three modes of vertical,45°tilt and horizontal all conform to the industry standard;the average flow rate is 1.74L/min.The droplet coverage field test shows that:under the same spraying mode,the droplet coverage of the canopy is in the order of left layer>middle layer>right layer,and the droplet coverage of different canopy heights is in the order of canopy height 1m>0.6m>1.4m;The size of the canopy and the growth state of the canopy and the growth condition of the appropriate spraying mode can effectively improve the droplet coverage and the utilization rate of the liquid.The spraying parameters were all in accordance with the relevant standards in NY/T 650-201 Operational Quality of Sprayers.This paper provides an effective solution to the problems of high labor intensity,low mechanical integration,poor adaptability,and inability to accurately vary pesticides in hilly and mountainous areas,and provides theoretical and technical support for the research and development of miniaturized,integrated and precise machinery in hilly and mountainous 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