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Soil testing is the basis for nutrient recommendation and formulated fertilization. This study presented a brief overview of potentiometric electrochemical sensors (ISE and ISFET) for soil NPK detection. The opportunities and challenges for electrochemical sensors in soil testing were discussed. [ABSTRACT FROM AUTHOR]

The control system of laser leveling machine was redesigned and tested to improve the performance and decrease the cost. In this paper, the control system of the machine which contains transmitter, receiver and controller was introduced. The receiver had silicon photoelements as photoelectric sensors. A kind of light filter was designed which was composed of red color optical glass and interference filter. Fussy control theory was applied in the controller design. The experiments conducted in fields showed that the controller and the laser receiver developed matched well. The control system worked well and the leveling accuracy was improved. [ABSTRACT FROM AUTHOR]