Study On Variable Rate Fertilization Control System Based On Sensor's Location

Precision agriculture is to use GPS, GIS and remote sensing (RS) techniques, access to every operating unit of farmland soil properties and crop growth characteristics, use intelligent expert system to make decision according to the specific circumstances of each farmland, according to the decision message of every operating unit of farmland, variable input seed, fertilizer, irrigation investment in water and other agricultural resources. Precision Agriculture Field implementation of variable rate fertilization, you first need to determine the location of field fertilizing machine, and then the variable controller controls the fertilizing machinery for the variable operation under the operating decision-making instructions. To determine the location of variable rate fertilization in precision agriculture is one of the most important technical aspects. Most domestic and abroad use DGPS positioning to determine the location of the variable rate fertilizer, two sets of GPS systems, base station and mobile station need to be installed, expensive; while GPS signals are often subject to weather, the external environment, human and other factors, the positioning accuracy and stability will decrease. Therefore, to ensure the requirements of precision agriculture variable operational, and the same time, reduce the positioning cost of variable rate fertilizer is the main direction. Combination of low accuracy of GPS and dead reckoning (DR) and other integrated positioning method can reduce costs, but the system structure is complex and reliability is poor; sensors accuracy, the information access and processing speed, sensors anti-jamming capability will have a great impact on integrated positioning; multi-sensor information fusion technology is flawed, difficult to practice.In 2005, Zhang Shuhui and other people exposed patent application"virtual GPS variable rate deep fertilization system in precision agriculture", In this paper, based on the patent, and on the problem of high input cost of precision agriculture variable operation, analyze and research the agricultural vehicle location technology, to search for a positioning way of variable rate fertilizer for China's situation in order to reduce input cost, to promote better application and extension of the variable rate fertilization technology in our country, achieve sustainable agricultural development.According to the characteristics of most farmland is forest belt division and more regular in Northeast China, with the guidance of sustainable agricultural development thinking, under the basis of farmland map of precision management, designed a block grid recognition algorithms and developed variable rate fertilizer positioning system. Use the speed sensor combined software programming to achieve the variable fertilizer's self-positioning. Developed a variable rate fertilization control system based on sensor's location. The final field experiments demonstrate the feasibility of the positioning method and working accuracy of the control system.(1) Make precision management of the block map. Collect block boundary data using AgGPS132 equipment and AgGPS70. Draw block boundary map and grid map using MapInfo Professional 7.0 software. Apply GPS and DCAS software for different grid sampling to get soil, yield and other field information, combined with the decision support system to generate work prescription plan. Repair the grid map and extract parameters for automatic grid identification. And put the prescription information and automatic grid identification parameters stored in the variable rate control system. On the basis of the map precision management, the regular and irregular automatic grid recognition algorithm derived in detail. In the field operation, the controller reads the map management data, recognize the fertilizer applicator's position by the automatic grid recognition algorithm.(2) Design location system of the variable rate fertilizer applicator. Use the speed sensor collecting wheel speed signal, ARM controller reads the speed sensor's pulse signal, calculating fertilizer walking distance, to complete fertilizer's automatic grid identification using the automatic grid identification algorithm. As the distance measured by sensor will result in a cumulative error, in this paper, accounting of various factors that generate cumulative errors, gives a cumulative error correction method to improve the positioning accuracy of the system.(3) Develop variable rate fertilization control system. The system is based on the prescribing information control, in the provision of per unit area fertilizing amount, by controlling the stepper motor's rotation speed to control the axis of fertilizer to achieve variable rate fertilization. The system has manual and automatic modes of variable rate fertilization: about the manual mode, the operator input fertilizing amount through the keyboard, combined with the operating speed, output frequency pulse calculated by the fertilization formula to control the fertilizer axis speed to achieve manual variable rate fertilization; about the automatic mode, after the extraction and processing of the speed sensor's signal, the system can correctly recognize the block grid, fertilization query and control fertilizer output variably. In the working process, the driver only has to press turn pause function key when the fertilizer applicator prepare to turn, and after it turned, continue the automatic grid identification and variable rate fertilization by pressing the Enter key.In the analysis of the control system's functions, stability, performance price ratio and other requirements, use ARM S3C44B0X core embedded controller as a platform for hardware design and software development. Hardware design includes S3C44B0X interface design, keyboard interface and functional design, sensor's signal processing circuit and motor drive circuit design; on the platform ofμC/OS-Ⅱembedded operating system, designed software application program corresponding to the hardware functions. Programming with C and ARM assembly language, using the ARM integrated development tools ADS1.2 for the process of program's development, compilation and simulation debugging.(4) A field experiment on this developed sensor-based positioning variable rate fertilization control system to test the feasibility.①Test the fertilizer's positioning accuracy on the soil surface of conservation tillage. First acquired the accumulated error correction coefficient is 0.967 on this soil surface. Block grid ridge length is 40m, to meet the subject requirement of less than 6% positioning error, the accumulated error should be less than 2.4m. After correction the positioning distance of the system can achieve 1150m, shows that the positioning system can meet the positioning requirements for 1150m long ridge of conservation tillage. According to the statistical data of 63 blocks in 6 villages of the town of Gongpeng in Yushu, Jilin province: the block number of the longest ridge that no more than 1000m accounted for 87% of the total blocks, area accounted for 65%. Therefore, the positioning system can meet the positioning requirements for most of our protective operation in Northern.②Test fertilization accuracy of the control system. In the circumstances of setting the grid fertilizing amount in the range of 250-400kg/hm2, the average fertilizer error of the system is 3.09%, achieve the requirements of variable rate fertilization.The innovation of the text is to design an automatic grid recognition algorithms based on the map precision management, developing a no-GPS positioning system of variable rate fertilizer applicator. The significance of the study is, compared with the DGPS positioning technology, the system has the advantage of low cost, simple structure, convenient operation and high economic efficiency, has some practical value in the field of precision agriculture. The positioning system fit the operational requirements of conservation tillage soil surface, has better economic and ecological benefits, and has far-reaching significance for the protection of arable land and the achievement of sustainable agricultural development.