Throughout history, most fertilizers used to increase the production of plants were organic. Colonial farmers used a combination of 'muck' and fish in an early form of compost to improve the yield of their plants. Advancements in chemistry in the 20th century saw many farmers turn to chemical fertilizers. However, in recent years, organic farming practices have led to the development of organic fertilizers and a return to compost to improve the soil.
Nitrogen is the primary building block of all life. Although nitrogen is present in the air, plants are typically not able to take advantage of its presence. Instead, plants must draw nitrogen from the soil. Nitrogen in organic fertilizer helps to keep crops green and boost the yield of plants. Green plant wastes, such as grass clippings, clover or kitchen scraps, make a good source of nitrogen for fertilizer because they release nitrogen into the soil as they break down. Animal manures are another good source of nitrogen.
Phosphorus is present in all living cells. Because of this, phosphorus is a building block for all forms of life. In animals, phosphorus is most present in the teeth and bones. About 80 percent of all the phosphorus in the mammalian body is present in the teeth and bones. Commercial chemical fertilizers mine fossilized fish bones for sources of phosphorus. An abundant, organic source of phosphorus is bone meal, which is made from the pulverized bones of cows.
Potassium is also found in the cells of every plant and animal on the earth. It is the seventh most abundant element in the earth's crust. Potassium helps plants with stalks to grow strong and tall. Potassium in chemical fertilizers is mined from the ground. In mammals, potassium is located in the muscles, skin, blood, digestive tract and liver. It follows, then, that good sources of organic potassium can be found in wood ash (the burned stalks of trees), blood meal and the stalks of dead and rotting plants such as tobacco stalks or corn stalks.