Design and Test of Variable-rate Fertilization Control Device of Precision Planter for SoybeanWANG XinzhongCollege of Engineering Heilongjiang Bayi Agricultural UniversityDaQing, Chinandwxz@WANG XiCollege of Engineering Heilongjiang Bayi Agricultural UniversityDaQing, Chinandwangxi@Abstract—Utilizing the favorable condition of Heilongjiang reclamation area carrying out the precision agriculture sample, we have developed an automatic control device with the variable rate fertilization. This device adopts industrial control computeris upper machine and variable rate fertilization controller for single chip computer as the core is lower machine, it is to be usedto the accompaniment of 6-line soybean precision planter, and it uses an electric control CVT(Continuously Variable Transmission) which controls the transmission ratio of discharging fertilizer system of the planter to change the volume of applying fertilizer. We carried out planting tests of the variable-rate fertilization with this control device on the 852 farmin Heilongjiang province in 2005 and achieved good results.Keywords-component; precision agriculture; variable rate fertilization; planter; computer;I.I NTRODUCTIONPrecision agriculture develops on the basis of 3s technology, it uses the ability of GPS on precision orientation to measure the output of each unite in field which is often defined in square meter and the surrounding spatial and temporal differentia of plants, analyses the reason of the differentia, and then computes the real volume of materials such as seeds, fertilizer, chemicals and irrigating water according to the needs of each unite plant. All of these efforts helps to optimize outputs, decrease materials cost, gain the maximal economy and social benefit, protect environment and realize the goal of sustainable agriculture.The agriculture production efficiency is relatively low at present, and there is a common phenomenon of low resource using efficiency and input versus output ratio. The existed agriculture production is mainly implemented by large amount of agriculture materials such as fertilizer plunged into the field. The volume of fertilizer in each unite of plantation area is three times much of world’s level each year. Because too much fertilizers were used blindly, it causes a relatively low fertilizer use efficiency in China. By the expert decision system, variable rate fertilizing machine as the most important part of precision equipment can make variable rate fertilizing digital maps, deliver variable rate data to auto control system fixed in the planter to realize auto control fertilization and promote fertilizer use efficiency according to soil test data, corn yield data, field level elevation maps, variety of crop, local weather situation etc.II.MATERIALS AND METHODSA.SYSTEM CONSTRUCTIONThe variable rate fertilizer controller consists of AG132 type of GPS receiver, wireless data transmission receiver, onboard computer, variable rate fertilization control software, variable rate fertilization control driver, electric control CVT, 6-Q-105 type storage battery, fertilizer delivering system of soybeans precision planter, etc. The construction of variable rate controller is shown in Fig. 1.Fig.1 The construction frame of the variable-rate fertilization control device Fig.2 The planter of the variable-rate fertilizationThis thesis is the project supported by National High Technology Research and Development Program (namely 863 Program)(No.006AA10A310, 2003AA209090). Key Tackling Item in Heilongjiang Provence (No.GB04B703) and Important Science and Technology Project in Heilongjiang Provence (No.GB06B601)___________________________________B.PRICINPLEThis variable rate fertilizing controller is equipped on the domestic 6-line wind attracted soybean precision planter and is driven by the East Red 802 type tractor to execute planting, it’s position is fixed by a mobile DGPS and data is delivered through RS-232 into a computer fixed on the machine. The computer displays the planter position in the field on the LCD screen, reads variable rate fertilizing data corresponding to the location of the machine in the field from the variable rate fertilizing database, then transmits instruction into the variable rate controller. The variable rate controller controls the electric control CVT to change the transmission ratio and finally realizes the goal of changing fertilizer volume.C.DGPS POSITIONING SYSTEMThe 852 farm experimental base in Heilongjiang province uses Differential GPS which consists of a ground fixed GPS deviation rectify station and a mobile DGPS receiver. The DGPS position error under submeter which means error distance within 1 meter can meet the needs of agriculture production in contrast that of GPS 15 meter with RTCM deviation rectify way. A mobile DGPS receiver is constructed by a mobile Ag132 type receiver which is used for receive GPS signal and PCC wireless data transmit receiver which is used for receiving the differential GPS signal. The PCC wireless data transmit receiver communicates with Ag132 type GPS receiver through RS-232 serial interface.D.ONBOARD COMPUTERThe onboard computer is equipped with colorful LCD screen, CPU clock speed of 800MHz, windows 98 operating system, RS-232 interface which makes it convenient to communicate with Ag132 type of GPS receiver, equipped with PCMCIA data slot which makes user insert a CF data card to read and record variable rate fertilizing data.Fig.3 variable rate fertilization controlling computerE.VARIABLE RATE CONTROLLING SOFTWAREVariable rate fertilizing controlling software is written in Visual Basic 6.0. It can control variable rate controller through LCD screen installed on the machine, fulfill the management of the border and corner of each field, number and area of field gridding and variable rate fertilizing data, and create maps of borderline, gridding, and variable rate fertilizing level of each unit. It uses the ability of Visual Basic in reading and writing function, data file is in the form of ACCESS, has the function of inputting planter parameters which is different according to different planter, and all of these enhance the universal and compatible of the software.Fig.4 main interface of variable rate controlling software The software can display track of the machine by using a mouse to simulate GPS data change, receive DGPS positioning data and lookup corresponding data in the variable rate fertilizing database and then output this data in order to control variable rate fertilizing executing mechanism and feed back the result to the onboard computer.Fig.5 variable rate controlling softwareF.VARIABLE RATE CONTROLLERVariable rate controller using MCS-51 single chip microcomputer as the core element ,the control circuit consists of AT89C51 single-chip microcomputer, serial interface, reset and anti-interference circuit, power constant voltage circuit, power polarity anti-protecting circuit, motor driving circuit,voltage reference circuit, instrument amplifier circuit ,A/D change-over circuit and so on. The whole circuit was fixed in enclosure of casting aluminum alloy, and plugs and sockets of aluminum are used. for improving reliability The circuitprinciple is shown in Fig. 6.Fig.6 The circuit principle of variable rate controllerG. ELECTRIC CONTROL CONTINUOUSLY VARIABLE TRANSMISSIONonboard computer gives the orders of variable fertilizing, control the transmission ratio controlling equipment of the step less transmission, and different instruction corresponds to different ratio thus to fulfill the operation of variable rate fertilization. The fertilization instruction totals 100 with the range of 100 to 200. When instruction is 100, variable rate controller regulates the transmission ratio to 32.7, and 200 corresponds the transmission ratio of 17.4. The relationship between data instruction and transmission ratio is classified in table 1. The fitting curve of transmission ratio for an electric CVT is classified as Fig. 7.Table 1 relationship between data instruction and electric CVT transmissionratio data instruction 89 108 121134 179 191204Transmission ratio39.730.727.324.218.71817.7CVTFig.8 The electric control CVTIII. CALIBRATION AND ADJUSTMENT TEST OFFERTILIZER QUANTITY BEFORE SOWING The self-designed variable rate fertilizing equipment is fixed on a 6-line wind attracted soybean precision planter. Work of testing and demarcating fertilizer quantity is done before planting in the aim of finding out the relationship between fertilizer volume and data instruction. First outputs signal 200 which means the maximal volume of fertilizer, increases the height of planter, turns ground wheel of excluding fertilizer manually, receives the fertilizer falling from the single excluding mechanism, and then weighs the fertilizer. The maximal volume of fertilizer is calculated with formula (1).ha Kg B N D q Q /22670.01070.014.3348.01000014.310000max u u u u u u u uዄ1ዅWhere is Q max ümaximal fertilizer volume of planter (kg/ha );q üfertilizer volume of single row excluder (Kg ), turn ground wheel 10 round, excluding fertilizer volume is 348g for geneva wheel excluder which is double rows.D ü virtual diameter of ground wheel (m), should take into consideration of tyres subsidence and slippage. Diameter is 0.70m.N ü number of excluder ground wheel turns with hand. in this experiment the ground wheel turns 10 round.B ü planter row distance, in this experiment row distance is 0.70m. When the fertilization instruction output by onboard computer is 200, the maximal fertilizer volume is 226 Kg/ha, and when the instruction is 100, the minimal fertilizer volume is 120 Kg/ha. According to calculating from the fitting curve and formula in Fig. 9, the relationship between fertilizer volume and data instruction is classified as Table 2.Table2. relationship between fertilizer volume and fertilizing data instruction data instruction 100115 128 140 153179200fertilizing volume120139 151 169 187210226Fig.9 The fitting curve and formula of fertilizing volume. y1 indicates curve of real fertilizer volume change; y2 indicates fitting curve of fertilizer volumeIV. TEST OF VARIABLE RATE FERTILIZATION AND PLANTING IN THEFIELDThe test is carried out in 852 farm of Heilongjiang province which is considered as the precision agriculture demonstration base. A sampled test of soil was carried out in the field in April, 2005 before nitrogen layer map, instant phosphorus layer map, instant kalium layer map, organic matter layer map, and PH layer map were created with the AFS software. A variable rate fertilizing description map was created by the AFS software according to the real state of the farm and data from description map was transferred to the self-designed variable ratefertilizing software at the same time.Fig.11 Test field of variable rate fertilizing for soybeanV. CONCLUSIONTaking advantage of 852 farm as precision agriculture demonstration base, we designed and developed a variable rate fertilizing controller and installed it on the domestic 6-line wind attracted soybean precision planter and achieved good results through learning and mastering the technology of variable rate fertilizing technology for precision agriculture in foreign countries.VI. REFERENCES[1] Wang Xinzhong, Wang Xi, Wang Chun, etal. Application test ofsoybean sowing by veriable fertilization seeder in Heilongjiang reclamation areas [J]. Transactions of the CSAE. 2008,24(5):143-146(in Chinese)Fig.10 Planting operation record figure of variable rate fertilizing for soybean[2] Liang Chunying, Yi Shujuan, Wang Xi, etal. PID control stratgy of theveriable rate fertilization control system [J]. Transactions of the Chinese Society for Agricultural Machinery. 2010.41(7):157-162(in Chinese) Heilongjiang Bayi Agricultural University cooperating with Baihua farming machines Factory of 852 farm fixed the self-designed variable rate fertilizing equipment on a 6-line wind attracted soybean precision planter which was refitted at the same time in 2005, and then developed the soybean precision planter with GPS. In the field of science research station on this farm, a variable rate fertilizing and planting experiment of soybean (Fig.11)was carried out by the planter which was driven by the East Red 802 type tractor. 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