The solution to a major agricultural problem is a little gross, but it’s necessary.

Future 1: It’s a world with intermittent food riots stemming from rising and unpredictable fertilizer prices, declining crop yields, and collapsing farm profits. Toxic algal blooms are spreading in the world’s lakes, and the Gulf of Mexico dead zone is the size of Michigan. Trade ambassadors of the United States and Europe pay regular visits to Morocco, negotiating arms deals and special trade relations in the hopes of keeping the fertilizer coming. It’s a crappy world getting crappier.

Future 2: It’s a world with abundant production from rich green fields fed by a resilient and reliable fertilizer supply that is recycled regionally and locally by a new industrial sector built on energy and nutrient recapture from food waste, manure, and sewage. Cities are now part of the farm. Low, stable fertilizer prices mean enhanced food security for all. Lakes and rivers are clean and supply abundant fresh drinking water, while dead zones have recovered and coastal oceans support sustainable fisheries for a rich source of protein. It’s a crappy world getting better!

These two futures hinge on what happens during the coming decades as supplies of high-quality phosphate rock become so depleted that it no longer pays to dig them up. Why’s phosphate so important?  Because it’s a bedrock of modern agriculture.

First some facts about phosphorus (P). P is a chemical element and exists almost entirely in the form of phosphate (PO4 3-). Since P is a chemical element, we can’t make any more, unless you have a supernova explosion under your control. Likewise, we can’t destroy it. For millennia, geology has allowed phosphate to slowly accumulate in ancient seabed formations in just a few lucky locations around the world. P is essential to all life (it’s literally in our DNA), including plants—such as agricultural crops. So, without phosphate, the breadbasket of America would be empty.

This brings us to where we are now. The Green Revolution, the major mid-20th-century expansion of global food production, relies in large part on fertilizer, to the tune of approximately 20 million metric tons of P in fertilizers applied in 2012 worldwide. Without it, agricultural productivity would have to get by with phosphorus that gets into soil by natural weathering of P from Earth’s rocks, which would only yield about 10 percent of what’s currently used—and would be wholly incapable of supporting our current population, much less the 2 billion to 4 billion additional humans expected for 2050.

Where does all this phosphorus for fertilizer come from? From mining operations focused mostly on ancient P-rich geological deposits that are concentrated in just a handful of countries, with Morocco having the lion’s share—about 75 percent at last report. China, in second place, has only 5.5 percent, and the United States trails in seventh with about 2 percent. These reserve estimates, however, can change surprisingly quickly. For example, Morocco’s estimate increased roughly tenfold essentially overnight in 2010, when an economic geologist took into account information from an old report that had been overlooked for more than two decades. So, while short-term concerns about the dreaded “peak phosphorus” have faded somewhat, we still have a P supply dominated by just a few global players. U.S. phosphate fertilizer production has been on a steady decline since about 1940, as prime sources have been depleted and environmental concerns constrain remaining operations. Extrapolating this trend, the United States will become entirely reliant on imports within roughly three or four decades.

Globally, phosphate is on something of a conveyor belt: It’s removed from rich geologic deposits and then gets dispersed widely around the world. Today P is accumulating in overfertilized agricultural soils in Europe and the United States or is running off from fields as erosion and leaching. The P that is captured in crops ends up largely in forms that are less than appetizing. Livestock eat it from P-rich feeds and then something becomes piled high and deep and it contains a lot of P. Nontrivial amounts of P also are in the food that we waste—and in the food that we eat and turn into our own waste.

This global P conveyor belt dumps much of its load into rivers, lakes, and coastal oceans where it makes a mess—algal blooms (including toxic forms) and dead zones. In one shocking example from 2007, nutrient runoff into China’s Lake Taihu combined with an unusual warm spell to produce such a massive bloom of toxic cyanobacteria that the city of Wuxi had to shut down its drinking-water supply and truck in bottled water for well over a million people for more than a week. Meanwhile, the fertilizer-fed dead zone in the Gulf of Mexico varies in sizes that are compared to various Northeastern U.S. states, Connecticut in one year, New Jersey the next.

 What stands between our current world of mined fertilizer and increasingly nasty water and the sometime-in-the-future alternative worlds of scarcity and mayhem versus abundance and sustainability?

The best opportunity for lowering our demand for mined P is to recover and reuse P from agricultural and human wastes. Animal manures, food-processing wastes, and human sewage constitute about half of the P on the conveyor belt to the environment. These waste streams offer the most immediate route to recovery and reuse because most of the P is in slurries of organic solids that also contain high amounts of energy. Anaerobic digestion, in which specialized microbes chew up organic matter in the absence of oxygen while producing methane gas, or microbial electrolysis cells, in which bacteria generate an electrical current that leads to hydrogen gas, are excellent means to convert the organic materials into highly valuable energy outputs. These microbial processes release the P as phosphate, which can be captured in clean, concentrated, and convenient forms for reuse in agriculture. Using microorganisms this way would give us three valuable things: renewable energy, concentrated P, and water with most of its pollution removed. All three contribute to economic, food, and environmental sustainability. These technologies aren’t yet reliable and cost-effective, but their eventual deployment could create whole new industrial and job sectors. Implementing these technologies allows fertilizer production to become regionally distributed and self-sustaining, and thus resilient against global geopolitical perturbations.

That still leaves the phosphorus that comes from erosion and drainage from agricultural fields. The best option would be to take all measures to reduce erosion and maintain healthy soil, as capturing and reusing this P once it has escaped the field is a much greater challenge. The P is in low concentration, attached to soil particles, and not accompanied by the energy-rich organics that enhance economic viability. Also, erosion and runoff often come in sudden, large flows associated with storms. Methods to remove and capture P from these flows are not as close at hand as technologies for the organic-rich slurries. Continued improvement of precision fertilizer application will also be needed, assuring that P finds its way to the crop, where it belongs.

Another strategy to help close the P cycle is to shift the human diet away from meat consumption. Only 10 percent of the phosphorus that animals eat ends up in our meat—much of the leftover goes onto the P conveyor belt to spoil our water. But even if we eventually recycle all manure, lowering meat consumption will still help reduce pollution by reducing farm runoff because we won’t need to grow so much feed for livestock.

Different recovery and reuse strategies can cut the input of mined P from its current rate of 14 million metric tons per year to almost zero, while lowering P pollution to the environment by about 80 percent. Complete energy and P capture from the organic slurries can lower mined-P demand and P pollution by almost 50 percent, while providing renewable energy. Then, reducing P loss from erosion and drainage by 50 percent—realistic through a combination of more precise fertilizer use and capturing P from contaminated waters—achieves almost an 86 percent reduction in mined-P demand. By adding the third step—reducing meat consumption by 50 percent—we can get the mined P to a minimal level and cut P pollution by almost 80 percent. (Achieving all of these measures will be made easier if human population peaks at lower levels in coming decades, closer to 8 billion than the daunting 11 billion included in some projections.) As we take these steps, upward pressures on fertilizer prices will ease, enhancing fertilizer access for farmers in the developing world so they can raise their crop yields and achieve food security.

So, what world future will be realized? Will our descendants be buffeted by a global resource battle over a dwindling fossil P supply that also threatens their drinking water? Or, will they prosper in a food- and water-secure world, nourished by a distributed, resilient, and sustainable fertilizer supply? We have tools for food and water security. Will we use them?

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