Introduction: Phosphate as an Essential Mineral
“The story of phosphorus is a long, fascinating one. But we are here interested primarily in knowing about its role in agriculture,” wrote Vincent Sauchelli in “Manual on Phosphates in Agriculture” published in 1942.
“Therefore in order to start at the beginning or our story we shall have to go back to the year 1840 – the year when Justus von Liebig, a German scientist, made an historical address before the British Association of Science in which he for the first time gave a clear, intelligent exposition of the role of minerals in plant growth and laid the ground work for modern agricultural science. He was the first to show that insoluble phosphates such as bone could be made to release their phosphorus in a form more quickly accessible to growing plants if they were caused to react with sulfuric acid. That suggestion stimulated John Bennett Lawes, an Englishman, to treat coprolites, a phosphorus bearing ore fairly abundant in Great Britain, with sulfuric acid and to test the resultant phosphate as a plant nutrient. In 1842 Lawes was given a patent on this idea, which permitted him to establish the first ‘superphosphate’ works. From then on is fertilizer history.
Within 20 years after Lawes got his patent the British were producing 150,000 tons a year of superphosphate. Then occurred the discovery of sources of mineral phosphates – rich deposits of rock phosphate in South Carolina in 1867 and in Florida in 1887. These discoveries gave American industry the opportunity to take the lead in the mining of rock phosphates and the production of superphosphate – a lead which has been maintained ever since.”
In a message to the United States Congress in 1938, President Franklin D. Roosevelt underscored the importance of phosphate to agriculture and people.
“The phosphorus content of our land, following generations of cultivation, has greatly diminished,” President Roosevelt said. “It needs replenishing. I cannot over-emphasize the importance of phosphorus not only to agriculture and soil conservation but also the physical health and economic security of the people of the nation. Many of our soil deposits are deficient in phosphorus, thus causing low yield and poor quality of crops and pastures…”
Phosphorus (P) is required by every living plant and animal cell. Deficiencies in available P in soils are a major cause of limited crop production. Phosphorus deficiency also is probably the most critical mineral deficiency in grazing livestock, according to “The Effect of Soils and Fertilizers on Human and Animal Nutrition,” U. S. Department of Agriculture (USDA) Information Bulletin No. 378, issued in 1975. When P fertilizers are added to soils deficient in the available form of this element, increased crop and pasture yields ordinarily follow.
Phosphorus is one of the primary nutrients essential for plant growth and crop production. It is a non-renewable resource that must be mined from nature. It cannot be artificially produced. We do not, however, mine phosphorus itself. We mine phosphate minerals.
Phosphorus is highly reactive and is not found in its elemental form in nature. It occurs in nature as phosphate, which is a charged group of atoms, or an ion. It is made up of a phosphorus atom and four oxygen atoms (PO4) and carries three negative charges. The phosphate ion combines with various atoms and molecules within living organisms to form many different compounds essential to life.
Some examples of phosphate’s role in living matter include:
- Giving shape to DNA (deoxyribonucleic acid), which is a blueprint of genetic information contained in every living cell. A sugar-phosphate backbone forms the helical structure of every DNA molecule.
- Playing a vital role in the way living matter provides energy for biochemical reactions in cells. The compound adenosine triphosphate (ATP) stores energy that living matter gets from food (and sunlight in plants) and releases it when it is required for cellular activity. After the energy, in the form of a high-energy phosphate bond, is released the ATP becomes a lower-energy adenosine diphosphate (ADP) or a still lower-energy adenosine monophosphate (AMP) molecule. These will be replenished to the higher-energy ATP (or ADP) state with the addition of phosphate by various mechanisms in living cells.
- The forming and strengthening of bones and teeth.
Humans get phosphate from the foods they eat. These examples show the amount of phosphorus* (mg/100 grams) in various foods.
Lean Beef 204
Wheat Flour 101
Cheddar Cheese 524
* NOTE: Although phosphorus is not found in elemental form in food, by convention the phosphate content of foods is expressed in terms of its phosphorus content.
Plants get phosphate from the soil along with nitrogen, potassium and a number of other nutrients they need to thrive. Fertilizer is added to nutrient-deficient soil to replenish these vital chemicals. Animals get phosphate from their food.
The bulk of the phosphate we mine – about 90% – is used to produce phosphate fertilizers. Another 5% is used to make animal feed supplements. The remaining 5% goes into making a variety of products from soft drinks to toothpaste to metal coatings.
Phosphate is a limited resource that cannot be replaced. As such, an international group of earth science and mineral resource agencies have designated it a strategic mineral resource. This group includes Australia, Canada, the Federal Republic of Germany, the Republic of South Africa and the United States of America.
“The International Strategic Minerals Inventory Summary Report – Phosphate” (USGS Circular 930-C) is a cooperative effort of this international group and was published in 1984 by the U.S. Geological Survey. It describes Phosphorus as “an important component of the cell tissues of plants and animals; it is necessary for the structure, growth, and propagation of living organisms. Phosphorus enters the organic food chain from the soil through the roots of plants. The human body contains about 1 percent by weight phosphorus, most of it in the bones and teeth. The human body requires a daily intake of 0.6-0.7 g of phosphorus.”