The average composition of the manure in pounds per 1000 gal of manure was 60 pounds of nitrogen, 30 pounds of phosphate (P2O5), 35 pounds of potash (K2O), 7 pounds of sulfur and 1 pound of zinc.
At the same time, I’ve seen prices quoted for commercial fertilizer in the range of $800/ton for anhydrous ammonia (82% N), $600/ton for phosphate and $800/ton for potash. Applying these values to the above manure analysis, the manure is worth $42.80/1000 gallons as it is removed from the pit.
For a wean to finish barn, you get about 340 gallons of manure per pig space per year or a net value at time of land application of $9.25 per pig space. For a 1250 head facility, this is $11,560.
When applied at 180 pounds of nitrogen per acre (3,000 gallons per acre), this becomes 8.2 pig spaces per acre from a grow-finish barn with a total land need of 150 acres.
Now, to put this into perspective, I'll give you the scoop on pig poop. To use a chemical fertilizer it will cost a farmer around $200 to $300 per acre; whereas for manure, we only pay what it cost to run the machinery--which doesn't even come close to $300 per acre. We also apply manure for other farmers and charge a fraction of what it cost to use chemical fertilizers. Furthermore, according to recent Canadian research manure actually helps rebuild topsoil. I think we can safely say that manure isn't waste, it is one of the most valuable byproducts from pigs. And, with proper waste management it can be an invaluable renewable resource for farmers.
Here is another scoop on pig poop: