raschemmel:
pH Sensor Kit - SEN-10972 - SparkFun Electronics
What's wrong with this ? (see attached files)
From the page:
Physical: this sensor is probably not compatible with direct soil measurements. The connection will be poor and you can easily break the thin bulb. If you’re careful not to poke any gravel or twigs into the glass you could try mixing up some mud using deionized water and measure that.