Nutrients exist naturally in the earth's soil and atmosphere, and in animal manure.
However, naturally occurring nutrients are not always available in the forms that plants can use. Therefore, man-made fertilizer is vital to food production. Farmers, ranchers and gardeners add these fertilizers directly to the soil, where they can be absorbed by plants for healthy growth. Incorporated into a program of best management practices, which includes soil testing, man-made fertilizer use leads to higher crop yields and greater environmental protection. In 1950, the average U.S. farmer produced enough food to feed 27 people.