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In order to improve precision of fertilization and efficiency of water and fertilizer utilization in the field, which can further promote flexible application of irrigation and fertilization technology in the field, the mobile irrigation and fertilization machine of precision fertilizer in the field was designed. Firstly, the mechanical design of mobile walking frame, precision fertilizer dispensing device and the first pivot device of integrated machine was carried out. Secondly, taking wheat as an example, based on the amount of water and fertilizer needed by crops in different growing periods, combined with the realtime measurement of soil moisture information, a threestage automatic fertilization time distribution model and a dynamic calculation method of mother liquor concentration were designed. A mathematical model for dynamic control of mother liquor concentration was established. A PID switching control method with Smith predictor was designed to rapidly stabilize the concentration of mother liquor, and the control method was simulated by Simulink to verify the difference of dissolution time of different types of granular fertilizer. On this basis, the central control system of integrated machine was designed, which integrated the time distribution model of irrigation fertilization and the dynamic control method of mother liquor concentration to realize automatic irrigation fertilization function and accurate control of mother liquor concentration. Finally, the experiment of irrigation and fertilization was carried out in the field environment. The response curve of EC of the injector was measured and analyzed. The results showed that the response curve of EC was changed in three segments, which indicated that integrated machine can carry out automatic operation of field crops according to the designed time distribution model. Because of small error fluctuation, short transition time, steep slope and small overshoot, the EC value of fertilization stage was stable, which indicated that the proposed switching control method can quickly stabilize the concentration of mother liquor for different types of granular fertilizer. The research of this machine was of great significance to the field integration and automatic precision irrigation and fertilization.