| As the planting area and output of apple trees,the most popular fruit in China,are gradually expanding and steadily increasing in recent years,China has become the world’s largest producing region of high-quality apples.Base-fertilizer fertilization as the most important fertilization method in annual production of apples,can supply the nutrients needed for the entire growth cycle of apple trees and create good soil conditions for the growth and development of the trees,while reducing the amount of chemical fertilizers added,improving the quality of fertilization,and increasing the effect of fertilization.In all,it is a way to realize the sustainable development of the fruit tree industry.At this current stage,the way to fertilize apple orchards with base-fertilizers in China is still dominated by manual operation for the low degree of mechanization,featuring high operation intensity,low fertilization efficiency,and poor fertilization effect,which has severely restricted the development of China’s apple industry.The mechanized base-fertilizer fertilization can reduce labor intensity and labor costs,and is a key measure to achieve fertilizer cut,quality and efficiency improvement in apple orchard development.In this paper,the agronomic requirements of base-fertilizer fertilization for apple trees and the physical and mechanical properties of soil and fertilizers were considered to develop a double-row ditching-fertilizer machine for orchards;meanwhile,its key technology and operational performance were tested and studied.While focusing on the agronomic requirements of ditching and fertilization for apple trees and the physical and mechanical properties of soil and fertilizers,we designed the whole structure and key components of the double-row ditching-fertilizer machine targeted at orchards,and applied the discrete element numerical simulation software to dynamically simulate the operation process to analyze the stress and movement process of soil and fertilizers,a way to optimize the key structure and operating parameters of the machine.Meanwhile,we explored key grain shape traits that affect the crushing of fertilizers to reduce the crushing rate of fertilizers in operation while building a fertilizer fragmentation force prediction model based on the grain shape traits.In conclusion,the orchard double-row ditching and fertilizer machine serves to solve the problem of mechanized spraying of organic and chemical fertilizers into a deeper depth for apple trees,improving the efficiency of ditching and fertilization and the effect of fertilization,and is of great significance to enhancing the mechanized production of the apple tree industry and the reduction of chemical fertilizers added while boosting efficiency.The main research contents and results are listed as follows:（1）The overall structure of the orchard double-row ditching-fertilizer machine.Considering the agronomic requirements of apple tree ditching and fertilization,we designed the whole structure of the machine as well as key components related such as the ditching device,fertilizing device,and automatic depth adjustment device for ditching following theoretical analysis.The core control system based on STM32F103 was then built to realize the integrated operation of apple tree ditching,mixed fertilizer application in depth,and earth covering.（2）The physical and mechanical properties of soil and fertilizer.Methods including oven drying method,cutting ring method,soil compaction measuring instrument,slope sliding method and free fall method were employed to measure and analyze the basic physical and mechanical properties of soil and fertilizers,in order to get basic data to establish an accurate discrete element model for“soil,fertilizer,soil-ditching cutting,and fertilizer-machine body”.The test results show that as for the cultivated layer,plow pan layer,and subsoil layer,the soil moisture content is 15.20%,17.44%,and 18.72%,the soil density is 1.67 g·cm-3,1.76 g·cm-3,and 1.80 g·cm-3,the soil compaction is 1508 Pa,1715 Pa,1848 Pa,the angle of repose of the soil is 35.58°,41.10°,and 48.20°,and the soil Poisson’s ratio is 0.36,0.40,and 0.42,respectively.The static friction coefficients between the contact surface and the three layers are 0.41,0.53,and 0.58,the dynamic friction coefficients are 0.08,0.16,and 0.19,and the restitution coefficients are 0.39,0.50,and 0.54,respectively.As for organic and compound fertilizers,the moisture content is 8.25%and 1.12%,the density is 1.05 g·cm-3 and 1.33 g·cm-3,and the angle of repose is 17.71°and 16.27°,the rigidity is 76.58 N/mm and 88.69 N/mm,the static and dynamic friction coefficients of organic,compound fertilizer with steel plate are 0.30 and 0.23,and 0.26 and 0.18 respectively,with the coefficient of restitution being 0.29 and 0.38.（3）Key technology of double-row ditching-fertilizer machine in ditching operation at orchards.The ditching mechanism of the orchard double-row ditching-fertilizer machine was studied to establish the kinematic model of soil particles,the key test factors that affect the quality of the ditching operation were analyzed,and the discrete element calibration of soil particles was finished in EDEM.Besides,the stability coefficient of ditching depth,ditch bottom width consistency coefficient,and soil coverage rate as test indicators were applied to build a regression model with test factors via Box-Behnken test design method,to analyze the interaction and influence of each factor on the test indicators,and comprehensively optimize each test factor to obtain the optimal operation parameter combination:the machine forward speed is 0.8 km/h as a whole,with the ditching cutter rotating at a speed of 348 r/min and in a deflection angle of 32°,when the depth stability coefficient in ditching is 98.33%,and the bottom width consistency coefficient is 96.32%,and the earth covering rate is 81.53%.（4）Mixed deep fertilization technology with double-row ditching-fertilizer machine in orchards.The fertilization mechanism of the orchard machine was studied to establish the kinematic model of fertilizer particles,which is used to analyze the key test factors including fertilizer screw speed,fertilizer sprocket speed,conveyor belt speed,guide plate angle,that affect the quality of fertilization operation.The uniform distribution coefficients of chemical,organic and mixed fertilizers as test indicators were applied to establish a regression model with each test factor,which is used to analyze the interaction and influence of each factor on test indicators;furthermore,the comprehensive optimization of each test factor was achieved to get the optimal combination of operating parameters:a fertilizer screw speed of 70 r/min,fertilizer sprocket speed of 45 r/min,conveyor belt speed of 200 r/min,and guide plate angle of 35°,when the fertilizer uniform distribution coefficients of chemical,organic and mixed fertilizers are 93.58%,91.12%,and 95.25%,respectively.（5）Fertilizer screening technology on grain shape traits.In order to reduce the fragmentation rate of fertilizers under orchard double-row ditching-fertilizer machine operation,we independently developed an analyzer based on binocular vision to non-destructively measure the particle shape traits of both compound and organic fertilizer particles.In addition,a prediction model of fertilizer crushing force was established by Support Vector Machine（SVM）and differential evolution algorithm,based on which the key particle shape trait parameters affecting fertilizer crushing were explored,and the optimization range of compound and organic fertilizers in particle size deduced thereby is 4.30～5.44 mm and 3.90～4.60 mm,respectively.（6）Whole machine development,performance test and field test of the orchard double-row ditching-fertilizer machine.The design parameters were applied to develop the orchard double-row ditching-fertilizer machine,the efficiency and performance of which were verified on site in terms of ditching depth consistency,uniformity of fertilization and fertilizer crushing rate as key test indicators.The test results show that the crushing rate of organic and compound fertilizers after screening is less than that of each fertilizer before screening.The crushing force prediction model of the fertilizer and the set particle size optimization range are reasonable and effective;the orchard double-row ditching-fertilizer machine can realize the integrated operation of double-row ditching,mixed deep application of organic and chemical fertilizers,and soil covering in orchards.The stability coefficient of ditching depth is no less than 95.25%,the consistency coefficient of the bottom width is no less than 95.59%,the soil cover rate is no less than 81.09%,while the distribution stability coefficient of organic fertilizer is no less than91.92%,the distribution stability coefficient of chemical fertilizer is no less than 92.40%,and the distribution stability coefficient of mixed fertilizer is no less than 94.02%.The evaluation indicators meet the technical requirements of ditching and fertilization for fruit trees. |
