Most dairies need no commercial fertilizer if they use manure properly. In most cases, manure can supply all the nitrogen, phosphorus, potassium, and several other nutrients needed for forage production. More than half the nutrients in dairy rations are excreted in manure. The key to managing manure is to treat it as a resource by recycling these nutrients to produce forage. For example, one lactating dairy cow's manure can supply enough nitrogen for 1.5 acres of silage corn.
Cows remove nutrients from feed for metabolism and milk production.
Some nutrients leave the farm in milk, but most are excreted in manure and remain on the farm. Manure applications return nutrients to the soil, where they can be reused to produce more feed. Figure 1 illustrates nutrient flow through a dairy. Figure 2 shows a cow's daily feed intake and where the nutrients end up. Note that more than half the nutrients in feed are excreted in manure.