Precise Variable Fertilizer Applicator For Winter Wheat Based On Canopy Spectral Reflectance

Nitrogen is one of the most active factors affecting winter wheat growth and development, therefore a reasonable utilization of nitrogen fertilizer can improve the yield and quality of winter wheat, otherwise result in fertilizer waste, yield and quality decrease,and even environmental problems. Variable fertilization technology is an authentic approach to rationalizing the use of nitrogen fertilizer. However, present variable fertilizer applicator are depend on the soil testing and fertilizer recommendation to carry out base-fertilizer, little study on the precise variable fertilizer applicator for jointing-stage winter wheat have been done, leading to a lack of variable fertilization machine based on the real-time monitor of plant site. Thus, this paper contraposed the nitrogen agronomic requirements and technical indicators of jointing-stage winter wheat to design a precise variable fertilizer applicator for winter wheat on the basis of near-earth spectrum detection technology, and correspondingly structured an intelligent control system for the applicator,and carried out experiments to confirm the reliability.The main research contents and conclusions are as follows:(1) The shaft sectional, double variable regulating technical scheme based on the near-earth spectrum detection technology was proposed; a variable fertilizer applicator was designed. The paper also studied the actuator of fertilizer: the rotate speed of fertilizer actuator was controlled by a continuous current dynamo, the open degree of fertilizer actuator was controlled by a stepping motor. Two independent control units for each side of the applicator were designed, which can achieve the adaptive control to distribute their speed and open degree, realizing the goal of real-time online changing of fertilizer consumption.(2) An intelligent control system for the variable fertilizer applicator was designed.The STM32 microcontroller was used as the lower computer to accomplish the job control of variable fertilization applicator,data acquisition,data analysis,data processing and data storage, a closed loop feedback control of the controller would be generated via receiving applicator job information form the related sensors. The human-computer interaction interface was developed by the configuration mode, users could complete parameters setting and data searching on it; the supporting software system for the variable fertilization applicator was exploited based on the principle of modular program design.(3) The best spectrum sampling and data processing frequency of the variable fertilization were invested. It is assumed that the spectrum data reflects spatial growth variation of wheat in field, decreasing the data processing load of variable control system and increasing the enforcement efficiency of the system, the experiment results showed that:the best frequency was 1 Hz. Nitrogen fertilizer optimization algorithm based on improved Ruan model was proposed, 11 nitrogen fertilizer levels was used for guiding field fertilization operations: when the normalized differential vegetation index (NDVI ) lower than 0.25or higher than 0.75, the target fertilizing amount was 0; when the NDVI was between 0.25 and 0.75, each level was determined on interval of 0.05.(4) By analyzing the working principle of outside slot round fertilizer apparatus and the fertilizer consumption calibration under different speed and opening degree, the study used Bisquare estimate robust regression to construct the control model of fertilizer apparatus; and analyzed the control strategy of double variables fertilization, designed three kinds of control strategies: control of speed priority, control of open degree priority and speed-open-degree adaptive control. Eventually, the target control sequence generation rules of bivariate adaptive control strategy was decided, a best combination of open degree and speed table was built, making speed-open-degree adaptive control achieved by looking up the table.(5) Studied optimization algorithm of fuzzy PID control to realize the adaptive control of variable fertilization. Analyzed the model and transfer functions of rotate speed and open degree sub-control unites. Designed the fuzzy PID controller. The initial values of the fuzzy PID controller were decided by particle group algorithm based on the ITAE principle.Analyzed the differences between fuzzy PID control and conventional control. Data indicated that the fuzzy PID control was superior to the conventional control, the study determined the system time response of variable fertilization applicator and corrected the fertilizer placement lag.(6) The performance study was done to confirm the reliability of variable fertilization machine. The results showed that a high precision of velocity measurement was equipped,the system average velocity error was less than 0.26 m/s.; the spectrum monitoring system had high robustness, the variation coefficient of multiple measurements were all less than 0.86%; the control error of left-right control system of variable fertilization was 9.85% and 9.63%, the average control error of the machine was 9.74%, the control accuracy was over 90%, indicating a good system performance of the machine.(7) Field experiments were operated by the self-designed variable fertilization machine. Results showed that: the error of variable fertilizer applicator was small;variable fertilization improved the group structure of wheat, and the yield tended to equilibrium, while wheat grow in traditional quantitative fertilization section had a poor group structure, and a high variability of yield; Yield of wheat grow in precise variable fertilization section was slightly lower than those grown in farm conventional management section, but with no significant difference between the two section, the precise variable fertilization realized the high yield of winter wheat;. Among different fertilizers application area of variable fertilization, with the increase of the fertilizer consumption, winter wheat yield also accordingly improved. For different varieties of winter wheat, the effectiveness of the variable fertilization was dissimilar.