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The alchemy of urine and guano

Phoshorus Mirabilis and the fate of growing systems



By Erin Volheim

Hennig Brand, a 17th-century German alchemist, one day found himself dabbling with human urine in an attempt to recreate the proverbial philosopher’s stone (which is not to be confused with a kidney stone). Instead, the distillation process produced not gold but a white, glow-in-the-dark material that burned brilliantly, and was thus named “miraculous bearer of light” or phosphorus mirabilis.

Forward another century or so and the German naturalist and explorer Alexander Van Humboldt came upon high-phosphorus guano piles on an island off the coast of South America—guano piles reportedly over 100-feet deep at the time of their discovery in the early 1800s. Such phosphorus-rich guano eventually was introduced as an alternate source of agricultural fertilizer in Europe by mid-century, but by the start of the 20th century the stocks were nearly depleted.

In 1847, James Lawes patented the first phosphate fertilizer, 
made out of bones treated with sulfuric acid; it has been theorized that early agrarians noticed that the best grapes grew in old battleground bone yards.

Historical stories aside, to fully absorb the elemental truth about phosphorus is to understand that it is as precious to life as water and the sun, and infinitely more important than oil. Next, find clear awareness in the knowledge that phosphorus cannot be synthesized; its supply is finite. Unlike nitrogen, which can be synthesized from the air by some plants, phosphorus either exists or it does not. Finally, take heed in the fact that to raise plants and animals for food, phosphorus must remain present in bodies and soil.

While plants thrive in phosphorus-rich soils, the animal body needs phosphorus to build and repair bones and teeth, for healthy nerve function and to contract muscles. Most of the phosphorus contained in the phosphate is found in bones, and the rest is stored in tissues throughout the body. And whether they know it or not, each year humans eat through three million tons of phosphorus mirabilis, excreting nearly 100 percent of it, as the kidneys normally filter unneeded phosphate into urine.

As important to agriculture as it is, a simple form of phosphorus does not exist in soil. It always combines with other elements to shape complex minerals and organic compounds. The total phosphorus content of soil six inches deep from the surface could be 200 pounds per acre in very sandy soils to over 2,500 pounds per acre in fine textured soils. Only a tiny fraction of this is in a phosphate form readily available to plants. Therefore, agricultural practices that build reserves of phosphorus are integral to the longevity of healthy soils.

Phosphorus from guano is still used as a high-end fertilizer for specialty crops, while untreated bones and bonemeal continue to be used by organic growers as slow-release phosphorus fertilizers.


Stripping at the Mine

Today, most conventional phosphate fertilizers come from mined phosphate rock. And while the most important use of phosphorus is as fertilizer, it is also employed in making weapons, the herbicide glyphosate (aka Round Up), baking powder and detergents, among other things. Yet few nations have access to enough phosphorus to supply their own long-term domestic agricultural needs. The majority of the world’s phosphate is controlled by China, Morocco and the United States, and in 2008, China established a 135-percent export tariff to protect their supply, the world’s largest known reserve.

Historically, the world’s biggest consumer, importer and exporter of phosphate fertilizers has been the United States, yet according to a US Geological Survey report on phosphorus, in 2006 only about 25 years of domestic phosphate remained. In response, U.S. fertilizer manufacturers are importing large supplemental quantities of phosphate from Morocco, which supplies more than a third of the world’s phosphate from the non-self-governed territory of politically distressed Western Sahara.

With various “peak phosphorus” theorists predicting that the point at which supply falls behind demand will be around 2040, with all currently known reserves potentially exhausted within 50 to 100 years, then it is arguable that only those countries who can afford to purchase it will be able to grow food in those years—unless they have been nurturing their soil on a nationwide basis. Yet on the brighter side, it is feasible in the course of a year for most diversified farms to transition away from using rock phosphate on their farms while implementing alternative phosphorus inputs and retention strategies.

Surprisingly, even today, ignorance of the phosphate-supply issue continues in alternative agriculture education. In their new book, Advancing Biological Farming: Practicing Mineralized, Balanced Agriculture to Improve Soils and Crops, authors Gary F. Zimmer and Leilani Zimmer-Durand communicate zero concern about global rock phosphate depletion and, in course, offer no alternatives.

The alarm of phosphorus’ short supply timeframe is based upon the assumption that demand for phosphate fertilizers will continue to grow in the United States and whether phosphate-exporting countries will be able to keep up with the rising demand by opening new mines or increasing production in the existing ones. Neither is a true solution though.

Concurrently, demand for phosphorus is growing with population growth, forced higher by the increased consumption of meat in countries like China and India. Based on European practices, the Swedish Environmental Protection Agency estimates that a plant-based diet uses about half the amount of phosphorus per person per year compared to a meat-based diet, adding greater credit to an agrarian vegetarian lifestyle.

Demand for phosphate fertilizers in the United States could decline if agricultural production is affected by droughts or by other climate-related events, slowing down domestic consumption of phosphate rock and temporarily conserving resources. Yet whether these cloudy predictions come true on time isn’t the point; there is a clear need now for farmers to quickly implement and improve positive phosphorus-sequestration practices.


Going with the Flow

In a recent study of phosphate pollution in the Mississippi River and Gulf of Mexico, researchers initially thought farmers were at fault for applying too much fertilizer, but new modeling research examined phosphorus loading from all 1,768 counties in the Mississippi River basin and found instead that urban sewage runoff was the largest contributor. Phosphorus from domestic sewage, in addition to fertilizer runoff, triggers blooms of algae that deplete local waterways of oxygen. One researcher estimated that of the billion tons of phosphorus mined since 1950, about a quarter now resides in water bodies or landfills.

In some wastewater plants, phosphorus can also bind with ammonia and magnesium to form the mineral struvite, which keeps the phosphorus out of waterways but clogs pipes at the facilities. Here phosphorus is an untapped resource but not something most domestic wastewater treatment plants are consciously filtering out of waterways.

In Japan and Sweden, major research has gone into recycled urine as a source for agricultural phosphorus. Urine contains nitrogen, phosphorus and potassium in correct ratios for plant growth. Anyone can use fresh urine diluted 1:10 parts water to feed plant soil (like any fertilizer though, avoid getting it on the leaves and rinse off leafy vegetables before eating).

If all human urine was to recycled, according to Jan-Olof Drangert of Linköping University in Sweden, it could supply half the phosphorus needs of the world’s cereal crops. In Sweden, two municipalities have mandated that all new toilets divert urine away from solid waste. The urine is collected in tanks at one’s house or in a communal collection point, and then picked up once a year by farmers.

In the United States, the first full-scale commercial nutrient recovery facility began operating in 2009 near Portland, Oregon. Owned and operated in an innovative public-private partnership, Ostara’s Pearl® nutrient-recovery process is removing more than 90 percent of the phosphorus in the wastewater’s liquid stream and producing 500 tons of Crystal Green® fertilizer annually. The facility serves more than 500,000 customers and will share revenue from the commercial sale of the fertilizer with Ostara. It is anticipated that the initial investment of the technology will be paid back within five years. Innovative technologies like this could be a practical phosphorus alternative for farmers with income to purchase it.

Worms, Gophers and Mushrooms

Nature-based solutions to phosphorus depletion rely on farmers supporting organic processes. Earthworms freely break down organic matter and convert it to more soluble forms of phosphorus and other essential nutrients thriving in a no-till agricultural system. The worms burrow through the soil to bury organic matter, create tunnels for water infiltration, improve soil structure and reduce soil erosion. The success of continuous no-till systems comes through a slow, but steady, increase in soil organic matter, improved soil structure and availability of soil nutrients.

In 2005, a 25-year study on zero tillage presented by Texas A&M professor and research soil chemist John Matocha, showed that soil phosphorus increased substantially in surface layers over time in no-till plots. The study’s authors found a 50-percent increase in phosphorus in unfertilized, no-till soil, and approximately a 100-percent gain in extractable soil phosphorus when they used soil-test recommended rates of nitrogen and phosphorus, compared with conventional tillage.

Even if farmers minimally till, incorporation of compost into soil will also reduce both phosphorus and nitrogen losses from compost application. When assessing potential runoff from fields, note that phosphorus tends to move downhill and is less likely to leach vertically into groundwater. On alkaline soils, research shows that it is best to use composted or vermicomposted manure to minimize environmental impacts. Before purchasing any amendments it is important to assess what implements are needed to spread the material on the field and when best to apply it.

Whether farmers learn to live with them, it’s undeniable that gophers are doing good things for the soil by aerating and fertilizing, moving minerals like phosphorus up the substrate. An agricultural system that purposefully balances them could create a mutual benefit for the farmer and the gopher. While this, in theory, would certainly be harmonious, there has been little advancement in this area and it’s proven to be a hard sell.

In a no-till soil system with a functional food web—including, bacteria, decomposer and mycorrhizal fungi—the phosphorus needs of most plants are met with or without the gopher. Part of it comes from the work of bacteria and decomposer fungi in breaking down plant residues. The balance is supplied by mycorrhizal fungi as they exude acids and enzymes that dissolve phosphate compounds in soil and rock into plant-usable elements and then transport the minerals back to the plant roots.

Whether farmers till or not, cover crops like buckwheat can bio-accumulate available phosphorus, drawing it up from almost four feet below the surface. During decomposition the phosphorus slowly releases back into the soil. Large increases in soil tests for phosphorus have also occurred within three centimeters of forage radish taproot holes.

Acres USA recently released a new book, Organic No-Till Farming: Advancing No-Till Agriculture by Jeff Moyer. The book demonstrates that tractors can be utilized in a no-till system, allowing for increased production and decreased labor. Annual cover crops are planted in the fall, overwintered until mature in the spring and then killed with special tractor implements. A special attachment, called a “roller-crimper,” is being used by some farmers, who then use driller attachments for seeding into mulch.

Organic No-Till Farming details a five-year transition plan to a no-till tractor system for willing farmers. If phosphorus peaks before oil, then farmers should at least be reading the road signs of global resource trends and turning their tractors, however slowly, in the right direction.


Erin Volheim homesteads and writes 
from Wilding Rural Education Center in 
Southern Oregon.


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