| Nitrogen is an indispensable factor for the growth of motor cells and plays a unique and pivotal role in the increment of crop yield.Crops at different growth stages have different requirements for nitrogen nutrition.Appropriately reducing the application rate of basic fertilizers and seed manure,and rationally applying the nitrogen fertilizers,could have an extremely positive and critical effect on the crop yield and grain quality formation.Variable-rate fertilization technology as an important measure for the implementation of a scientific and rational fertilizer input on demand,can effectively improve the effect of nitrogen fertilizer,enhance the production vitality of crops and ensure the food production safety.Currently,most of the existing research achievements on VRT in China is mainly focused on theoretical design and analysis of the narrow-row strip outer groove-wheel type fertilizer applicator that is based on soil testing and prescription recommendations.In addition,there is rare and exiguous study on key technologies for intelligent and efficient centrifugal variable fertilizer spreading equipment based on crop real-time growth information and on-line control.Therefore,an independently developed variable fertilizer spreading equipment suitable for cultivation in Southern China is necessary and of great significance,and to promote demonstration applications in the main grain growing areas where scale management and mechanization are advanced.Aimed at the demand for high-integration of agricultural machinery and agronomy in rice-production in Southern China,rice crops in rice-wheat rotation fileds were thus used as research objects in this study.A centrifugal dual-discs variable fertilizer spreader,which is suitable for large-scale modem agricultural planting areas,was developed based on the real-time spectral information acquisition and online fusion technology of crops in the Datian Area.Coupled intelligent variable regulator control system and an interactive software were also developed.Further,systematic performance tests and field experiments were carried out.The main reserach contents and conclusions are as follows:?1?A double-discs centrifugal variable fertilizer spreader based on spectrum sensing technology was developed for the rice field.An information collection device,fertilizer adjusting device and the spreading device were also designed.The centrifugal variable fertilizer spreader monitored the crop growth information in real-time through the GreenSeeker spectral sensors.The stepping motor regulated the opening of fertilizer distributor and the fertilizers were scattered by the centrifugal conical disc with reverse rotation in high speed,which accomplished the real-time variable fertilizer application according to crop spectral information.?2?An intelligent variable-rate control system for the developed fertilizer spreader was designed.Hardware system platform based on STM32F103 core controller was built to facilitate real-time information acquisition,online feedback and rapid processing.A control terminal with WLT102A8 embedded configuration industrial computer as the upper machine was constructed.C language was used to compile the system software control program in Keil development environment.The control program was a series process that entailed online data acquisition,fertilization decision-making,and variable execution.A touch-visual HMI that was based on structure control configuration to achieve the switchover between target function interfaces was also created.The switch-over between function interfaces was achieved by clicking on the button link.?3?Structure optimization and performance analysis of the variable fertilizer spreader were carried out by establishing discrete element simulation model based on discrete element method?DEM?.Virtual simulation tests of fertilizer spreading were designed using the EDEM software in combination with theoretical analysis of particle motion.The results indicated that the most significant factors that affected transverse distribution were order of pitch angle of vane,?,cone angle of disc,a,and spreader height,h.The optimal combination through response surface model?RSM?was a=10.35°,?=12.58°,h=88.88cm,providing a minimum Cv of 11.55%.Based on these working parameters,simulation tests of fertilizer spreading performance of the spreading device were performed and the test results showed that when pitch angle was 15°,spreading height was 95 cm,flow rate was 300 g/s,and rotational speed was 600 rpm?as critical speed?,the variation in the particle distribution curve was negligible and the spreader exhibited good spreading uniformity.?4?Consistency of the spreader fertilizer discharge and rationality of spectral data sampling frequency were studied,and the applicability of variable-rate fertilization model was modified.Test analysis showed that the linear correlation determination coefficient?R2?between the actual and theoretical values of system distributing flow rate was 0.99.The best objective characterization of spatial heterogeneity of rice-crop growth structure can be obtained when spectrum sample frequency f=1.6 Hz.The applicability improvement for nitrogen fertilization optimization algorithm?NFOA?model was implemented based on the fundamental situation of rice-production in Southern China.Reasonable division of fertilizer recommendation gradient by NDVI value?at interval of 0.05?was conducted to optimize the decision-making of variable?5?Effects of different controlled feed-gate flow rate and disc rotation speed on application rate per unit area and effective spreading swath width,respectively,were investigated.Variable-rate fertilization models were developed by analyzing particle distribution variation characteristics resulting from increasing and decreasing application rates.The results depicted that distributing flow rate had a significant effect on the fertilizer application density,and as such can ensure priority strategy of accurate fertilizer.In addition,the disc rotation speed mainly influenced the effective fertilizer swath width,and this in turn contributed to priority strategy of high efficiency fertilizer.Additionally,the proposed variable-rate fertilization model exhibited a high fit degree with an S-shaped function curve for both increasing and decreasing distribution rates,and this to some extent confirmed the prediction accuracy of spatial distribution,which could provide the guidance for subsequent multi-trajectory overlapping variable-rate fertilization.?6?Dynamic characteristics of adjusting actuator,formation mechanism of system response delay and fertilizer spreading lag were analyzed.The correction method for response delay of the variable control system was also put forward.Motion model including three kinds of fertilizer adjusting actuators and system distributing lag model were established.The screw slider actuator was selected from the optimization by system performance tests,and then the corresponding lag time correction Tlag = 1.74s was implanted to improve the fertilization distributing delay,that reduced the system control error,improved the distributor precision and overall performance of fertilizer spreader.?7?Related performance verification tests of variable fertilizer spreader were carried out.Verification tests showed that the coefficient of particle distribution variation,Cv was reduced by 20.3%after RSM optimized the structure parameters of centrifugal variable spreader under optimal working parameters combination.In comparison to the simulation tests,there was an error of less than 11.78%,which confirmed the feasibility of discrete element simulation analysis.Validation tests of the application rate model showed that the accuracy of forecasting model was above 83%.The correlation determination coefficient R2 between test values and predicted values were 0.91 and 0.82,respectively for increasing and decreasing distribution rates which confirmed the validity of the prediction model for variable fertilization and provided reference values for conventional empirical fertilization.?8?Systematic field tests were completed to embody the implementation effect of variable-rate fertilization.Field spreading tests showed that the error of average Cv and application rate error y were 9.19%and 9.25%respectively,and could satisfy the requirements of related regulations on fertilization machinery in contrast to performance tests.Performance tests of the variable-rate fertilization showed that system spreading precision was more than 80%,reduced the Cv of rice NDVI values in comparison to the conventional balanced fertilization,greatly improved crop growth population structure and spatial heterogeneity,and achieved a better economic,ecological and social benefit. |
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