Larryfos, I'm afraid that you have been fooled.
Those numbers "2.718282" and ".008985" and "0.207762" are totally nonsense.
Sticking two metals in soil and have one metal continuous 5V on it, that's just rubbish.
In some situations, with a certain type of soil or water, with a certain temperature, with certain metals, for a single measurement of the humidity, then it might work for one minute (just kidding, it will totally fail).
Sorry for my blunt post, I felt that someone had to say it how it is.
To measure the soil humidity, use a capacitive sensor as Aggertroll wrote.
Don't try to find a better resistance tester, use a capacitive sensor.
The only problem that you have to solve is if it is "capacitive" or "capacitative" :o