donutboy said:
sorry they would report back via radio or cell.
You could do that and you could do it with off the shelf gear. Most of the large farms have wireless moisture sensors deployed around them.
All you'll need it about $2000-$3000 initial investment in gear (depending on how many sensors you want to deploy) and then you'll need to sign up for a data plan which is going to run about $25/month. That assumes that there is actually cellular coverage where you want to set the network up. The sensors themselves are pretty cool - battery powered, solar recharged (could be a problem around here in the winter when you need the network most), batteries that are rated for about three years and environmentally hardened.
Juice's idea of re-creating the Galbraith Mud Index is a good one. If there is a school near the place you want to monitor, many schools participate in the "school net" of weather stations so you can easily scrape rain, temperature and wind data off the web. Do some corelation between the amount of rain, temp, maybe wind conditions with trail conditions and you probably have a pretty decent proxy for spending a bunch of cash on gear that's probably going to get busted up or stolen anyway.