Soil moisture sensors

I'm trying to use a Watermark soil moisture sensor in the my home automation project. I believe this sensor cannot be read as a standard resistive sensor using a DC voltage across the sensor, the voltage across the sensor must be A/C.

Also, Irrometer who make the sensor don't seem to want to giveout details of the sensor's response curve, and temperature correction details.

So,

Does anyone have, or know where i can get an interface circuit schematic diagram for the Watermark sensor.

Does anyone have, or know where i can get details of the response curve, and temperature compensation details.

Thanks in advance

Keith.