When talking about manure's value, one needs to think about a variety of factors. Most folks think of fertilizer nutrients as manure’s primary value or MVP, but it takes more than one or two star players to make a great team. As such, manure wouldn't be as great as it is without other characteristics like the added organic matter that you get when applying manure, or the microbial community that is added to your field with that application. The value of manure depends not only on the nutrient concentration in the manure, but also what the next crop requires, the condition of the soil, and whether or not commercial fertilizer will be used to supplement manure and make up for nutrient imbalances that often occur.
If you really don't need something, just how valuable is it? If you've got a really great team already, are you willing to pay a lot of money to transfer in a star player? To turn that around, if your soils are needing nutrients and could use some additional organic matter or microbial life, would you still sell the manure that could help you build that soil back up? It’s for this very reason that manure value changes for every field that it is applied to.
Source : unl.edu