Phosphorus was the 13th element to be discovered, and the first that was not known since ancient times. For this reason, and also due to its use in explosives, poisons and nerve agents, it is sometimes referred to as “the Devil’s element.”1, 2 German alchemist Hennig Brand is credited for discovering this element in 1669 when he distilled approximately 5,500 liters of human urine to produce 120 grams of a glowing substance which he ultimately named Phosphorus, from the Greek word for “light-bearing.”
For over a century, Phosphorus has had multiple functions in soil chemistry. Today we know that optimum levels of Phosphorus enhance early root formation and growth, flowering and seeding, uniform crop maturity, and stalk and stem strength. It is important for photosynthesis and respiration. Respiration is the process by which plants convert photosynthates such as sugars, back into energy for growth and other metabolic processes.
Soil Phosphorus is immobile for the most part and the level of soluble Phosphorus immediately available to plants is rather small. In order for plants to satisfy their need for Phosphorus, their root systems must explore large areas of soil. Mycorrhizal fungi greatly assist plant root systems in this exploration by forming a symbiotic relationship with them. The thread-like hyphae of the fungus connect with plant root hairs and extend great distances into the soil, taking up nutrients and transporting them back to the plants. This results in increased Phosphorus uptake. In exchange, the mycorrhizal fungi receive sugars and other compounds from the roots.
The uptake of Phosphorus can be limited by soil compaction, pH, and moisture. Even in high Phosphorus soils, anything that inhibits aggressive root growth, such as compacted soil, will have an adverse effect on Phosphorus uptake. With a pH greater than 7.0, Phosphorus can be fixed in less available forms by excess Calcium. With a pH of less than 6.0, Phosphorus can be fixed in less soluble forms by excess soluble Aluminum. Phosphorus availability is at its highest at pH 6.4 to 6.8. Optimum levels of Phosphorus will result in higher Phosphorus uptake at all moisture levels. However, moisture stress results in lower Phosphorus availability. Moisture levels exceeding soil capacity exclude the oxygen required for Phosphorus uptake.
Phosphorus is a highly reactive element and does not exist in elemental form in soil. Plant roots take up nearly all Phosphorus as phosphate. (P2O5) Orthophosphate is the simplest phosphate with the chemical formula PO4-3. Primary orthophosphate has a chemical formula of HP204–, is dominant in acidic soils, and is taken up much more readily than the secondary form, HPO42- that is the dominant available form of Phosphorus in alkaline soil conditions. All Phosphorus sources added to soil must be converted to the orthophosphate forms before plants can utilize them.
Organic, biodynamic, and biological farming/gardening practices utilize a direct application of rock phosphate as the source of Phosphorus. Colloidal soft phosphate rock and Tennessee Brown Phosphate rock are inexpensive, commonly available Phosphorus sources, both of which are approved for organic use by the USDA National Organic Program. Phosphate rock is a largely insoluble, slow release Phosphorus source. Only about 3% orthophosphate is soluble and readily available to plants. The rest remains “locked up” or chemically bonded to Calcium and is gradually released for plant use by the action of soil microbes. So the Phosphorus is long lasting, remains insoluble and in reserve, and is not subject to leaching. Optimum levels of phosphate rock in the soil contain enough “reserves” to provide the release of available Phosphorus in more than adequate quantities for early season requirements, as well as a continuous supply throughout the growing season.
Phosphate rock is also the raw material used to make highly mobile, water soluble Phosphorus fertilizers (WSP fertilizers) used by large scale farming operations. The global fertilizer industry consumes nearly 90% of the world’s phosphate rock production in the manufacture of WSP fertilizers. The remainder is used to make elemental phosphorus and animal feed supplements, or is applied directly to soils. Phosphate rock and sulfuric acid are the raw materials used in the manufacture of single superphosphate (SSP) and phosphoric acid. Phosphoric acid is an intermediate by-product used to make triple superphosphate (TSP) and ammonium phosphate. Highly concentrated, compound NPK formulations now form the mainstay of the global fertilizer industry (Engelstad and Hellums, 1993; UNIDO and IFDC, 1998).
Unfortunately, the high solubility of these concentrated NPK fertilizers, and their overuse in efforts to achieve huge yields of big, tall, expanded but nutrient deficient crops, is very detrimental to our environment. Unlike phosphate rock, which stays in the soil and releases its “reserves” of Phosphorus over time, superphosphate fertilizer is subject to leaching and runoff. Extensive use of concentrated NPK fertilizers destroys microbes, earthworms, and other beneficial soil organisms. The soil loses its beneficial texture and becomes less capable of absorbing water. Topsoil erosion becomes problematic and the runoff of rain carries soil particles, and the Phosphorus attached to them, into streams, rivers, and lakes.
Unnaturally high Phosphorus levels in these bodies of water fuel excessive growth of algae. In a process called “eutrophication,” these algae die, and are decomposed by bacteria that use dissolved oxygen. This creates “dead zones” resulting in fish kills, surface water scum, decreased recreational use, and foul odors.
Most phosphate rock is mined using large-scale surface methods. Michael Astera of Agricola has written one of the most insightful concepts regarding the mining of all minerals used in agriculture. It appears as follows:
“Mining of the needed minerals need not entail long-term environmental damage
either. Mines and quarries can be carefully worked by those who care about their
home planet, and when the mines are depleted they can be landscaped and
planted to be as or more beautiful than before mining. It’s also worth noting that
many of the economically viable sources for agricultural minerals contain such
high concentrations of these minerals that they are toxic to soil life and little or
nothing grows there. Removing these toxic concentrations and using them to
make other parts of the planet healthier and more productive can, at the same
time, open up these formerly toxic soils to the growth of forest or grasslands.
None of this should be done on the basis of greed or short-term gain, but rather
wisely, intelligently, and in harmony with Nature.”
Phosphorous, when present along with 10 other important minerals, all in ideal ratios to each other, results in a fertile soil capable of producing vigorous, nutrient-dense crops of superior quality. Such a mineral balance also works to sequester carbon, improve soil texture and drainage, provide adequate water retention, prevent erosion by water or wind, promote biological activity, and reduce costly annual inputs. Balancing the minerals in the soil is the first step toward sustainability because if the minerals are not in the soil, they can’t be in the food or recycled on the farm or in the garden.
Organic, biological, and biodynamic farming and gardening systems strive to reduce “outside inputs.” Once the minerals in the soil are balanced, you won’t have to add them in those quantities again. A soil test in the spring and fall will indicate any minor adjustments needed. Sulfur and Boron will be the minerals most likely needing attention as plants readily take them up. The superior health of a minerally balanced soil greatly reduces the need for inputs other than these minor adjustments. Since the minerals are in the soil, they will be in the crop residues, cover crops, and livestock manure and will be recycled through these sustainable systems.
Justus von Liebig, considered to be the founder of organic chemistry, popularized The Law of the Minimum. “The availability of the most abundant nutrient in the soil is only as good as the availability of the least abundant nutrient in the soil.” Whichever nutrient is in the shortest supply will limit the performance of the crop. This illustrates why balance, and optimum quantities of mineral nutrients, is so vital.
The Farming Systems Trial (FST) at Rodale Institute, is America’s longest running side-by-side comparison of organic and conventional agriculture. Over thirty five years of scientific data from the FST have proven that organic systems produce yields equal to conventional, outperform conventional yields in years of drought, build rather than deplete soil, and are actually more profitable than conventional farming.
We have focused on Phosphorus and its importance to sustainability. We have discovered that it takes a synergy of Phosphorus and ten other mineral nutrients to maximize soil fertility, and we have looked at just a few of Rodale Institute’s FST empirical, scientific findings. Moving forward in sustainability calls for the coming together of many ideas, scientific facts, and schools of thought.
1 Emsley, John (7 January 2002). The 13th Element: The Sordid Tale of Murder, Fire, and Phosphorus. John Wiley & Sons. ISBN 978-0-471-44149-6. Retrieved 2016-08-26.
2 Weeks, Mary Elvira (1932). “The discovery of the elements. II. Elements known to the alchemists”. Journal of Chemical Education. 9: 11. Bibcode:1932JChEd…9…11W. doi:10.1021/ed009p11.