It's simply a permanent store of wealth. Urea has a limited shelf life. The producer can't store urea for 5 years then sell it so what can they do to retain their value? Simple, accept 12,500 URO for equivalent purchase of urea today.
Take a look at gold in 1900, it was only $20 usd per ounce but is stable today well over $1000 usd per ounce. http://www.onlygold.com/coins/Gold-Double-Eagles.asp
In 1900 a lot of experts knew that the value of gold had the potential to reach over $1000 but they weren't willing to pay it because they can keep the gold for 100 years because gold will last 100 years. The is really no difference between gold and URO except for one major feature. URO protocol means that 1 URO = 1 tonne of urea. Obviously URO will last forever (like gold) and it's a store of wealth. Even if it takes 100 years to reach $300 per URO it's still a store of wealth. With URO you have the option of accepting it for urea and keeping it or you can go out any day in the future and get 1 tonne of urea or sit on URO for 100 years and watch it reach 300 usd. The interesting thing is though what happens if there is some world event that causes market price of 1 tonne of urea to reach $1000 per tonne? Simple, now 1 URO = $1000 ....
Look at what happened to the phosphate market (also a component of fertilizer). In the mid 2000's phosphate skyrocketed in price from $50 per tonne to almost $450 per tonne. This could happen to urea prices, there is no reason that they can't skyrocket to over $3,000 per tonne
http://www.infomine.com/investment/metal-prices/phosphate-rock/all/