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How to sense resistance with an arduino?

Is it possible to sense reistance between 2 poles or a material with an arduino.

The material's I want to read the resistance of are soil and water .

I know I can do it with a multimeter ,Im just asking if it is possible to do with an arduino and how.

Any suggestion?

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This is the original one I found when looking for information on the same subject. At the time I was looking at setting up a micro greenhouse.

http://www.botanicalls.com/archived_kits/twitter/

This is more of a full fleged setup....

http://www.instructables.com/id/Garduino-Gardening-Arduino/

This is what I want it for .

I want to make a watering notifiier.

You can use a basic voltage divider.

Connect 5v to a probe which you stick into the soil. Stick another probe into the soil and connect it to an analog input pin, then connect a high value resistor from the analog pin to GND. Adjust the resistor size for sensitivity. The voltage on the analog pin will be related to the resistance between the probes.