Switching soil moisture sensor

The utility model relates to a switching soil moisture sensor which is composed of a pottery clay head, a sensor body, a U-shaped mercury manometer, a brush-shaped switch, a zero setting pipe and a cover body, wherein, one end of the sensor body is connected with the pottery clay head, and the other end of the sensor body forms an air collection chamber; the cover body is sealed at one end of the air collection chamber of the sensor body; the U-shaped mercury manometer is sealed in the sensor body; an air column is closed off on one arm of a U-shaped tube of the U-shaped mercury manometer, and the top end of the other arm of the U-shaped tube of the U-shaped mercury manometer is sealed with a pressure sensing film; contacts of metal conducting wires are pressed on the other arm of the U-shaped tube of the U-shaped mercury manometer, wherein, one contact positioned below a mercury surface is near to the lower part of the U-shaped tube, and is always conducted with a mercury column, and the conducting wire which is connected with the contact is used as one external-connecting line of the sensor; connection conducting wires of the rest contacts are respectively soldered on soldering sheets of each step of the brush-shaped switch in turn; a movable contact sheet of the brush-shaped switch is connected with the other external-connecting line; the sensor is also provided with the zero setting tube, and an air valve is arranged on a tube mouth of the zero setting tube.