The following is an excerpt.
Fertilizer that comes from cows or other animals does not really originate with them. Manure from cows and other animals has been used as a crop fertilizer for millennia, and it is still used today for about 5% of US crop acres and for a high proportion of organic acres. It is often spoken of as an alternative to “outside inputs” for crops and as a superior option relative to “synthetic fertilizers.” However, just as Obama said about businesses and infrastructure, “you didn’t build that,” when it comes to fertilizers from animal sources we must also say, “they didn’t make that.”
Don’t get me wrong, I think that cows are wonderful. It is only because their complex, ruminant digestive system houses certain bacteria that we humans have access to the most abundant form of plant-stored solar energy – cellulose. Animals also do a rather good job of absorbing the mineral nutrients like nitrogen, potassium and phosphorus in their feed, but they are not 100% efficient at utilizing their dietary input. So, their manure still contains nutrients which can fertilize a crop. But the animals didn’t “make” any of those nutrients. For instance the ~2% nitrogen in cow manure came from whatever they ate (grass, corn, soybeans…) and those crops, except for the soybeans, were mostly fertilized with “synthetic nitrogen.” The cow is just passing a bit of that along.
View the original article here: No, Cows Don’t Make Fertilizer