Peak Phosphorus


As we deplete our reserves of mined phosphorus, will sewage sludge be the only way to feed ourselves?

By Amanda Kimble-Evans

Nitrogen, potassium and phosphorus. These three key nutrients are part of the foundation on which growing food is intimately reliant and is the basket in which the disciples of reductionist industrial agriculture have put all their metaphorical eggs. Phosphorous, specifically, is the focus of a recent report from the Soil Association that warns of a coming crisis, “Without fertilization from phosphorus it has been estimated that wheat yields could fall from nine tones a hectare in 2000 to four tones a hectare in 2100.” According to the report, the availability of mined phosphorus could even peak in the next 30 years.

What is the answer? The Soil Association offers a number of recommendations, focusing much of their effort on increasing the use of human waste as a fertilizer for farm fields both nonorganic and organic.

The real beef with biosolids

Treated human waste (otherwise known as sewage sludge or biosolids) has been indicated as a risk to human and environmental health for a multitude of reasons. The report addresses the heavy metals found to be problematic in the past, stating the levels have been declining in recent years. But, it does not, admittedly, discuss the more recent red flags such as antibiotics, hormones, steroids and other pharmaceuticals, or things like triclosan, flame retardants and solvents that end up poured down drains.

Researchers at Virginia Tech, for example, recently warned that excreted antibiotics spread on farm fields are contributing to antibiotic resistant bacteria and are a serious environmental problem.

And sewage sludge is already sprayed on conventional farm fields across the U.S. and the U.K. The only sector of agricultural land restricted from using biosolids is that of certified organic farms. “While nutrient cycling and a closed-loop system are key principles of organic agriculture, lifting the restrictions on sewage sludge for these farms would have very little impact on reducing the use of mined phosphorus overall and could open the gate for a whole host of new problems,” says Mark Smallwood, executive director at the Rodale Institute.

Coming down from the edge

A clearer and more direct path towards a more sustainable agriculture, less reliant on mined phosphorus, does exist. The following recommendations were touched on in the report to a lesser extent, but have the potential to make a greater impact with less risk to human and environmental health.

Smarter management: Phosphorus has made the news more often for its part in the Gulf of Mexico dead zone and algea blooms in lakes across the country than for its scarcity. The overuse of synthetic fertilizers and poorly timed applications of raw manures and biosolids have let this mobile mineral slip from the soils that feed us and into the waterways wreaking havoc all along the way.

Changing how we farm: Organic farming prohibits the use of synthetic fertilizers, and focuses, instead, on manure, compost, bone meal, or cover crops to provide the majority of phosphorus needs, effectively stepping out of the race for more and more mined phosphorus. Organic practices also pay heed to nurturing the micro-organisms in the soil which help retain and make available more of the phosphorus that is applied.

Changing how we eat: According to the Soil Association report, it takes more than twice as much phosphorus to support a meat-based meal as does a vegetarian meal, so reducing the amount of meat consumed will reduce our reliance on mined phosphorus. And when meat is on the menu, choosing grass-fed livestock grazed on organically-managed pasture is the best choice.

The use of mined phosphorus at breakneck speeds is a warning of yet another weak and crumbling pillar on which our primary agricultural system rests. Luckily, the awareness of our addiction provides an opportunity to invest in more regenerative systems for managing our resources, growing our food, feeding ourselves.

8 Responses to “Peak Phosphorus”

  1. Anonymous

    I have no desire to further mankinds explosive growth and destruction of the planet but this article is somewhat misleading. Phosphates come primarily from urine as opposed to the sewerage sludge mentioned in the article. In fact the first pure phosphorus was extracted from buckets of urine. In Sweden at least they are working on seperate toilet systems to capture urine. Bottomline. You can’t keep taking out and not putting back simply because we are sqeamish.

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  2. Ben

    Interesting discussion and comments! I try to take this discussion and article and make it relevant to my farming situation.

    I farm in Tasmania, Australia which has a small widely dispersed population with few metro areas where the recycling of human waste would be cost effective. This is the biggest hurdle to over come. while the concepts are sound if it doesn’t pay then it doesn’t happen!

    the sticking point is getting the treated waste back onto farmland in a cost effective way.

    the pig comment is interesting and we have seen the benefits of pig manures in our farming operation the problem is that pig production is no longer economically viable so we have ceased that enterprise and focused on sheep and cattle grazing with some cash cropping.

    I believe that to increase the viability of my farm i need to improve my soil health and pasture and we are part of trail work on composted poppy trash. But the success or otherwise will be mainly focused on the economic viability. while this is no way the be all and end all of striving to be more sustainable it is the elephant in the room that can’t be ignored.

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  3. Anonymous

    From the article above:

    “The overuse of synthetic fertilizers and poorly timed applications of raw manures and biosolids have let this mobile mineral slip from the soils that feed us and into the waterways wreaking havoc all along the way.”

    Phosphorus is actually pretty insoluble and as a result, is not very mobile in soils.. it’s the soils, soil water, topdressed/unincorporated manures moving off the landscape via erosion and runoff that primarily deposits the P from agriculture in waterways.. synthetic fertilizers hold only a fraction of the P compared to animal (and human) waste.. most of it is banded anyway, or should be…Use cover crops and related soil conserving practices to keep your soils where they belong..at your place..

    My concern is that when you balance your N requirement using manures or composts alone that you will undoubtedly be overapplying phosphorus.. food and field crops are really not that big a user of P in soils, but the P must be available to them.. you don’t get the uptake and removal to help keep your mass nutrient balance in.. balance…and you get inordinate buildup of P.. only a fraction of which is soluble each year..

    Show more work and value in banding of nutrients when and where the plants need them the most.. and contain the P from point sources (i.e. from a pipe – i.e. sewer pipe)via source separation and composting and we’d go a long way to cleanin’ the place up.

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  4. Anonymous

    I heard the director of the UC-Davis student farm speak at the Small Farm Progress Days in Grass Valley and I can quote him, “We’ve plumbed our society wrong.” He meant in earnest that the waste stream has changed from it it historically was – and we need to separate flows – black water, gray water, red water (pharmaceuticals, pesticides, etc. = red) and even yellow water (urine).
    The first principle of sustainability is “close the loop” on nature’s cycles. Or, imitate nature and recycle those chemicals that nature did not invent or use, like triclosan in soap. We can’t recycle red, black and gray water mixed into one flow.
    Red water inactivates septic systems. Antibiotics, for intance, stop the digestion that goes on in the anaerobic digester called a septic tank and in the aerobic digester called a leach field.
    Our centralized waste treatment doesn’t do the job it should, because estrogenic substances pass right through, creating a headache for the environment. Google “CSULB: Sex, drugs and radical chemistry” for Dean’s breakfast on waste, Dr.’s Kelley and Mazrk speaking, on waste issues.
    We need to reinvent the farm to make it nature-friendly and sustainable. This means waste recycling, waste of all kinds – I suggest that the Rodale Institute’s farm is not sustainable if the farm plan does not include a plan for human waste recycling.
    True, a host of diseases are associated with water contamination from human waste, like cholera from raw waste directly penetrating the aquifers that gave us drinking water; composted human waste loses some of its disease-bearing toxicity and can be applied to ground as fertilizer safely. See Gene Logsden’s HOLY SHIT book.
    Organic animal husbandry is good waste, waste in the traditional form that nature can handle and break down. However, there are limitations on what can be applied directly to fields, because phosphorus will leach off. In Texas, e.g. the Lake Waco watershed is polluted from concentrated dairy operations, and the farmers, to manage the burden of phosphorus have had to truck half the collectable manure out. You cannot exceed the carrying capacity of the land and claim a God-given right to pollute the environment that 1000′s of people share!
    Compost toilets anyone? Let’s work to close the loops that provide the vital ecosystem service of waste removal. Nobody can look hard at the environmental problems of today and not recognize the value of organic agriculture – it works!

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  5. Anonymous

    Sewage sludge. That unctuous concentrated ooze left after all the water is removed from the effluent of toilets, flushed pharmaceuticals, sewers, bodily fluids, dead stuff and chemically-bombed farmer fields. And they want to put it on organic fields? Is this a joke or is someone from Monsanto behind the idea?

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  6. Vic

    While integrated/sustainable farming methods are essential, so are integrated waste management systems. Many of the concerns related to sludge application could be resolved by separating our wastes upfront, i.e., urine separation. Most of the phosphorus we excrete is in our urine, which is biologically fairly clean (not quite sterile, but almost). Its when we mix urine with feces that we muck up our ability to efficiently and reliably recover phosphorus. Urine can be easily disinfected (via storage) and used as fertilizer. Although a portion of the “emerging contaminants” (like pharmaceuticals, endocrine disruptors, etc.) wind up in urine, many of these are effectively treated in a healthy, biologically-active soil matrix.

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  7. Anonymous

    So why not use pig manure, heavy on phosphorous, and forego the need to genetically modify the pig to produce less phosphorous in its manure?

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  8. Adam

    This article raises some really important issues! Yeah!

    But it misses some crucial facts…

    Smarter management depends on preventing EROSION, not leaching. Phosphorus is lost predominantly through wind and water erosion, which carries soil particles and nutrients away. This must be addressed by cover cropping, no and low till practices, etc.

    Changing how we farm does not change where our nutrients are coming from. Most organic agriculture depends on feeds or manures from conventional agriculture, which in turn comes from mined phosphorus. Human waste is the most available and concentrated form of phosphorus available. Waste that is not mixed with industrial chemicals, but is composted is completely SAFE for agriculture.

    Changing how we eat will not prevent phosphorus scarcity from occurring. Consumption is not an effective political action.

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