Since humans learned agrarianism and left their hunter-gatherer ancestors behind, manure — both human and animal — was the chief source of fertilizer. In the early 19th century, bat guano was discovered as a fertilizer source, resulting in an international trade in bat guano until global supplies were largely depleted by the early 20th century.
The discovery and development of synthetic fertilizers enabled the continuation of improvements in world agricultural productivity, in turn bolstering an exploding human population. However, these modern marvels still require basic elements to create, a chief essential ingredient being phosphorous.
Phosphorus is present throughout our planet, but phosphate rock (of which there are hundreds of varieties with differing compositions) has been the natural resource from which most of the world’s phosphate is commercially extracted. (There are quadrillions of tons of phosphorus in the Earth’s crust, but the concentration of 0.1% phosphorus is commercially unviable).
The United States production of rock phosphate peaked in 1980, at 54.4 million metric tons. In 2006, China surpassed America to become the world’s largest producer of phosphate rock. There are finite supplies of phosphate rock on the planet, with Morocco possessing the bulk of the planet’s reserves. But with growing populations and thus food demand, modern agriculture is completely dependent on this single resource for its sustainability, leading to debate over when the world will hit “Peak Phosphorus”:
The world faces an “imminent crisis” in the supply of phosphate, a critical fertilizer that underpins the world’s food supply, scientists have warned. … Phosphate use has quadrupled in the last 50 years as the global population has grown and the date when it is estimated to run out gets closer with each new analysis of demand, with some scientists projecting that moment could come as soon as a few decades’ time. At current rates of use, a lot of countries are set to run out of their domestic supply in the next generation, including the US, China and India. … “In a few years’ time, it could be a political issue with some countries effectively controlling the production of food by having control of rock phosphate supplies,” [Martin Blackwell, from Rothamsted Research, an agricultural research centre in the UK] said. “There should be a lot more effort being put in so we are ready to deal with it. It is time to wake up. It is one of the most important issues in the world today.”
Ironically, overuse of phosphates has polluted the oceans and American rivers, including Vermont’s waterways — the phosphorus from synthetic fertilizers dispersed on Midwestern fields is passed into grains (feed) trucked to cows in Vermont, where it flows as manure (along with commercial agriculture fertilizers, unless a farm is organic) onto the wet slopes and fields of the Green Mountains. Phosphate is an essential mineral for all life on earth — creating sustainable supplies without overburdening the ecosystem will remain a challenge.
Regardless of when Peak Phosphorus strikes the world, price volatility and international politics already threaten food security and food prices. The USDA reports:
Prices of phosphate rock, sulfur, and ammonia—raw input materials used to produce diammonium phosphate and other fertilizers—increased from January 2007 to early 2008. Moroccan phosphate rock contract prices tripled, international contract prices of sulfur increased more than 170 percent, and Tampa prices of ammonia doubled.
Facing short supplies, China increased its export taxes on fertilizers from 35 percent in 2007 to 135 percent in 2008 to ensure that domestic production remained in the country. China is the world’s largest exporter of urea—a major source of nitrogen fertilizer—and the second largest exporter of phosphate.
(I am unsure why wikipedia states China is the world’s largest exporter since 2006, and the USDA states it is second. I note the discrepancy).
A metric ton of rock phosphate was $31.50 in 1991, and rose only gradually by 2008, when it spiked. This was aggravated by ethanol subsidization and other factors, but the price hit $450/metric ton for the winter of 2008-09. By April of 2020 the price had calmed to $70.75, but has spiked in the last year to a current (October 2021) $147.50/ton, a 208% increase. Along with fuel oil price spikes, these inputs will compound in the food growing, processing, and distribution systems — food prices are going to rise, and phosphorus availability may one day single-handedly threaten the economic and human health of nations.
It has been estimated that probably half of all agricultural fertilizer in the United States could be supplied by animal manure, much of which is currently wasted in industrial systems designed to spray chemicals, not graze cows. This would also sequester carbon in soils, and reduce CO2 generation in commercial fertilizer production and shipping.
Alexandria Ocasio-Cortez derides cows as the enemies of the globe and the chief culprits of methane burps. Yet, ambulatory bovine fertilizing — aka rotationally-grazed grass-fed cows — are the best possible producers of fertilizer to replace Moroccan and Chinese rock phosphate, and they reduce soil erosion and retain precious water without overloading soils with excess phosphorus.
The sole other viable resource for non-synthetic phosphorus is human fecal matter: AOC has not yet disgorged her plans for that.