There is a reason dairy farmers have to buy fertilizer. Most dairy farms are very efficient at collecting all the waste the cows produce. They then empty the p

There is a reason dairy farmers have to buy fertilizer. Most dairy farms are very efficient at collecting all the waste the cows produce. They then empty the pits into a tanker truck and spray/inject it onto the fields. It goes a long way and helps complete the cycle, but your intuition is right, it alone is not enough.