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Professor Chris Rhodes

Professor Chris Rhodes

Professor Chris Rhodes is a writer and researcher. He studied chemistry at Sussex University, earning both a B.Sc and a Doctoral degree (D.Phil.); rising to…

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As Rock Phosphate Runs Out, What is More Important - Food Crops or Fuel Crops?

World rock phosphate production is set to peak by 2030. Since the material provides fertilizer for agriculture, the consequences are likely to be severe, and worsened by the increased production of biofuels, including those from algae.


The depletion of world rock phosphate reserves will restrict the amount of food that can be grown across the world, a situation that can only be compounded by the production of biofuels, including the potential large-scale generation of biodiesel from algae. The world population has risen to its present number of 7 billion in consequence of cheap fertilizers, pesticides and energy sources, particularly oil. Almost all modern farming has been engineered to depend on phosphate fertilizers, and those made from natural gas, e.g. ammonium nitrate, and on oil to run farm machinery and to distribute the final produce. A peak in worldwide production of rock phosphate is expected by 2030, which lends fears over how much food the world will be able to grow in the future, against a rising number of mouths to feed. Consensus of opinion is that we are close to the peak in world oil production too. Phosphorus is an essential element in all living things, along with nitrogen and potassium. These are known collectively as, P, N, K, to describe micronutrients that drive growth in all plants and animal species, including humans. Global demand for phosphate rock is predicted to rise at 2.3% per year, but this is likely to increase in order to produce crops for biofuel production. As a rider to this, if the transition is made to cellulosic ethanol production, more phosphorus will be required still since there is less of the plant (the "chaff") available to return as plant rubble after the harvest, which is a traditional and natural provider of K and P to the soil.

World rock phosphate production amounts to around 140 million tonnes. In comparison, we would need 352 million tonnes of the mineral to grow sufficient algae to replace all the oil-derived fuels used in the world. The US produces less than 40 million tonnes of rock phosphate annually, but to become self-sufficient in algal diesel would require around 88 million tonnes of the mineral. Hence, for the US, security of fuel supply could not be met by algae-to-diesel production using even all its indigenous rock phosphate output, and significant further imports would be needed. This is in addition to the amount of the mineral necessary to maintain existing agriculture. In principle, phosphate could be recycled from one batch of algae to the next, but how exactly this might be done remains a matter of some deliberation. e.g. The algae could be dried and burned, and the phosphate extracted from the resulting “ash”, or the algae could be converted to methane in a biodigester, releasing phosphate in the process. Clearly there are engineering and energy costs attendant to any and all such schemes and none has been adopted as yet.

Cleaning-up the Environment.

There is the further issue of the demand on freshwater, of which agriculture already struggles to secure enough to meet its needs, and in a sustainable picture of the future, supplies of water appear uncertain against the countenance of climate change. It is in the light of these considerations that algae/algal fuels have begun to look very appealing, especially given the claimed very high yields that can be obtained per hectare as compared say with rapeseed and biodiesel. Conventional algae production can be combined with water clean-up strategies3, to remove N and P from agricultural run-off water and sewage effluent, both to prevent eutrophication (nutrient build-up in water), which causes algal blooms, and to conserve the precious resource of phosphate. Algae might also be “fed” with CO2 from the smokestacks of power stations to reduce carbon emissions. The implementation of integrated strategies such as these, where the creation of a “carbon neutral” fuel is combined with pollution-reduction is thought to be the only way that the price of algal fuels can be brought down to a level comparable with conventional fuels refined from crude oil. As the price of oil rises inexorably, they are likely to become even more attractive. “Peak phosphate” is connected to “peak oil” since phosphate is mined using oil-powered machinery, and in the absence of sufficient phosphorus, we will be unable to feed the rising global human population, since modern industrialised farming depends on heavy inputs of phosphate, along with nitrogen fertilizers.
Pesticides, too, derived chemically from crude oil, are essential, along with oil-refined fuels for farm machinery. It is, nonetheless, doubtful that the world’s liquid transportation fuel requirements can be met through standard methods of algae cultivation entirely, though fuel production on a smaller scale seems thus feasible. An analogy for the latter might be as growing algae in a “village pond” for use by a community of limited numbers.

No solution to “fuel crops versus food crops” problem.

It is salutary that there remains a competition between growing crops (algae) for fuel and those for food, even if not directly in terms of land, for the fertilizers that both depend upon. This illustrates for me the complex and interconnected nature of, indeed Nature, and which like any stressed chain, will ultimately converge its forces onto the weakest link in the “it takes energy to extract energy” sequence. It seems quite clear that with food production already stressed, the production of (algal) biofuels will never be accomplished on a scale anywhere close to matching current world petroleum fuel use (>20 billion barrels/annum). Thus, the days of a society based around personalized transport run on liquid fuels are numbered. We must reconsider too our methods of farming, to reduce inputs of fertilisers, pesticides and fuel. Freshwater supplies are also at issue, in the complex transition to a more localised age that uses its resources much more efficiently.

In contrast to fossil fuels, say, phosphorus can be recycled, but if phosphorus is wasted, there is no substitute for it. The evidence is that the world is using up its relatively limited supplies of phosphates in concentrated form. In Asia, agriculture has been enabled through returning animal and human manure to the soil, for example in the form of sewage sludge, and it is suggested that by the use of composting toilets, urine diversion, more efficient ways of using fertilizer and more efficient technology, the potential problem of phosphorus depletion might be circumvented. It all seems to add up to the same thing, that we will need to use less and more efficiently, whether that be fossil resources, or food products, including our own human waste. We are all taking a ride on spaceship earth, and depend mutually on her various provisions to us. Our number is now so great that we cannot maintain our current global profligacy. In the form of localised communities as the global village will devolve into by the inevitable reduction in transportation, such strategies would seem sensible to food (and some fuel) production at the local level. "Small is beautiful" as Schumacher wrote those many years ago, emphasising a system of "economics as if people mattered".

And if we try to continue with business as usual?

There is a Hubbert-type analysis of human population growth which indicates that rather than rising to the putative “9 billion by 2050″ scenario, it will instead peak around the year 2025 at 7.3 billion, and then fall. It is probably significant too that that population growth curve fits very closely both with that for world phosphate production and another for world oil production. It seems to me highly indicative that it is the decline in resources that will underpin our decline in numbers as is true of any species: from a colony of human beings growing on the Earth, to a colony of bacteria growing on agar nutrient in a Petri-dish.

By. Professor Chris Rhodes


Professor Chris Rhodes is a writer and researcher. He studied chemistry at Sussex University, earning both a B.Sc and a Doctoral degree (D.Phil.); rising to become the youngest professor of physical chemistry in the U.K. at the age of 34.

A prolific author, Chris has published more than 400 research and popular science articles (some in national newspapers: The Independent and The Daily Telegraph)
He has recently published his first novel, "University Shambles" was published in April 2009 (Melrose Books). http://universityshambles.com

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  • Simon Tannock on June 21 2012 said:
    An interesting article Chris. You note that population rise is "in consequence of cheap fertilizers, pesticides and energy sources, particularly oil."
    One other major factor that has influenced population rise has been the efficacy of wastewater treatment. If everyone was still throwing our "night soil" bucket into the street, our population would not be where it is today.
    I believe it is wastewater treatment that also has part of the answer to the problem. You noted that growing algae in wastewater effluent is an option, and I think it is the only sensible one in biofuels production.

    It makes no sense to use new phosphate for algae production when its collection and use is easily done from wastewater effluent. So, new P for food, recaptured P for algae, and then perhaps capture the P from anaerobic digestate for food or algae again. This will greatly limit the losses or dilution.

    I imagine the lack of incorporation of AD plants and algae systems for nutrient recapture/recycle is a reflection of the infancy of the industry rather than either energy or capital issues. Where I work we are considering this as an essential part of closing that loop and achieving it is not an engineering concern at all.

    Where you raise points about the freshwater issue between food and fuel I think that this is where algae becomes the champion on the day compared to other crops. Algae can be grown in brackish and salt water, so freshwater is not the issue. Also, reflecting back to anaerobic digestors, these are also salt tolerant, so the P and N can be captured and recycled with concern for wasting freshwater.

    Its and exciting time for all those who are involved in this developing industry. I think the answer to your entitled question is "Rock Phosphate - Food crops, and 'then' Fuel crops!"
  • Durwood M. Dugger on June 22 2012 said:
    Chris, As always an interesting article. While you point some of the major concerns about biofuel development, perhaps I can offer a few more:

    1. In the US we have examined the economic feasibility of using algae to convert wastes to energy and or fertilizers yielded very highly limited (climate/seasonality/temperature/photo period, spatial - available processing area near waste sources,etc.) such only about 3% of total wastes were feasible for conversion. A good idea for can be, but far less than expected or needed for national energy solutions. Also, in the US 38% of sewage ends up in backyard septic tanks, not economically feasible for commercial biofuel usage. Further, estimates to redesign our sewage/waste infrastructure to collect and effectively process our wastes has been estimated as a 50 year construction task taking several trillion dollars. In a period where we are already in economic decline because of our loss of cheap energy and critical commodities - where would the money come from?

    2. Large scale algae biofuel production turns out to be self-limiting beyond just it's dependency on NPK. As we shift from fossil fuels to lower carbon emission alternative energy sources, the production of waste CO2 required in most commercial algae growth and economic (carbon credit) strategies - declines such that alternative energy becomes algae biofuel limiting in itself as a cheap source of CO2. In the very best case algae biofuel production at effective scales can only be considered as either a bridge energy source - from petroleum to actually renewable energy sources (solar, wind, tide, etc.), or as a last ditch energy source where survival at any costs over rules economics.

    3. No one that has seriously examined algae biofuel production concludes that it can make a significant energy contribution without the use of NPK - which 85% (95% if you include the confluence of petroleum in NPK production) of the world's food crops are also dependent upon. In the US the primary supporters of algae biofuels have been the US military (their concerns about US foreign energy dependency) that use 80% the country's petro-energy. What these military strategist don't seem to have considered is that biofuels are also foreign commodity dependent.

    According to the 2011 USDA Fertilizer Import Summary (online) - "U.S. nitrogen and potash supplies largely depend on imports. More than 54 percent of nitrogen (N) and 85 percent of potash (K2O) supply was from imports in calendar year 2011. Because domestic production capacity is limited, any increase in nitrogen and potash demands will have to be met largely by imports."

    A decade ago the US was a net exporter of NPK and it's most critical component rock phosphates (also the only known at scale economic source of ag. and ind. phosphorous) that supply the phosphorus (most critical element) in NPK fertilizers which are btw totally dependent on petroleum for their production today. We now import a growing amount of rock phosphate - 15% of our consumption in 2011. From where you should ask? Well, that would be largely from Morocco.

    This 2011 USDA Fertilizer Import Report begs the logical question - "If we have to import the fertilizers that we use for military biofuel and food production - how is that importation less risky, or a lower priority than importing foreign oil?" and "How does it reduce our critical dependency on foreign resources - especially in times of war where foreign dependency can be used against us as an effective weapon?"

    Algae biofuels and even terrestrial biofuels are neither renewable nor sustainable under current economic and technological paradigms - nor do they move the US away from critical foreign energy or commodity dependency. In reality they will make us even more dependent upon foreign phosphate producers not just for bio-energy, but for our food crops as well. Perhaps the US military should remember that old military adage - "An army travels on it's stomach." Today a modern military isn't just dependent on fuel, they are still dependent on adequate food as well. From both a technical and economic perspective regarding biofuels - fuel and food are the same thing.
  • Mel Tisdale on June 22 2012 said:
    This article shows just how irresponsible it is to fight action to control climate change.

    We are now at the stage where climate science is sufficiently settled to be able to say with confidence that dramatic action is necessary if we are to avoid what can only be described as a catastrophic temperature rise in the near future.

    Perhaps we should be demanding that those scientists and politicians who can be shown to be repeating long debunked myths about climate change be investigated for crimes against humanity. Especially if it can be shown that they are funded to some extent by the fossil fuel industry.

    "Money doesn't talk, it swears." Bob Dylan
  • CPL on June 23 2012 said:
    This whole article is about over population. Pretending like it is not the elephant in the room is silly.

    Besides there is no "peak" Rock wool. It's peak Oil all the way. Since we are in Peak Sweet Light Crude and Peak Diese right now, it is only a matter of time.

    You'll know it's bad when California starts to scheduel brown outs. Which are now being done.
  • Orsotoro on June 23 2012 said:
    All this is true, but there are new sources of Phosphate coming on-line throughout the world. Check out Sirius Minerals ( UK AIM : SSX ) which has discovered the largest / richest source of phosphates in the world, with its York Potash discovery in Yorkshire, UK. This is truly significant ( as significant as the iraqi Kurdistan oil discovery at Shaikan by Gulf Keystone petroleum Uk AIM : GKP )
    Both do not alter the fundamentals of a rapidly-depleting resource base, but it is interesting that both have been overlooked / under-publicised, for whatever reason.
    Worth investigating both, in the interests of balance / investment opportunity.

  • Feedtheworld on July 19 2012 said:
    A few things that need clearing up.
    Peak phosphorus is a myth, created by a bunch of accademics seeking glory. It has no scientific basis, applying a discredited theory (the Hubbert peak - look at the latest US oil reserve forecasts - more like a valley than a peak) and using out-of-date reserve data. Latest reserve data suggests at least 300 years and one analysis suggests 1000 years with more efficient processing and use and increased recycling. But hey, why let facts get in the way of a theory if it gets you published? You can always get an accademic friend to peer review it and praise your theory. See the USGS site or www.fertilizer.org/ifa/HomePage/SUSTAINABILITY/Phosphorus-peak-phosphate
    Sirius is nothing to do with phosphate - it's potash, and not really that big compared to other potash discoveries - of which there are a lot.Its not the largest or richest anything, just a possible mid-scale potash development. Most US potash imports come from Canada, just over the border in Saskatchewan. A lot easier to invade than Iraq if you want to get your hands on their reserves.
    There is a lot of new phosphate rock being discovered elsewhere however - Africa, Australia, Latin America.
    The US is still a major exporter of phosphate fertilizer - mostly using US rock from Florida, South Carolina, as well as smaller deposits in the West, although the US does import some phosphate rock, with some imported from Morocco, but also from a new mine in Peru.
    Only nitrogen fertilizer is particularly energy intensive in its production - phosphate fertilizer production is reasonably energy balanced (you get a lot of energy when you burn the sulfur to make sulfuric acid to process the phosphate rock into phosphate fertilizer.
    The US imports around half its nitrogen fertilizer, but with lower natural gas prices there is a lot of interest in building new plants in the US and that proportion will fall.
    All that said, using imported fertilizers (guess were most of the nitrogen comes from ? - the Middle East) and precious land to grow corn to make fuel is about as stupid as it gets. The net energy gain is minimal and may even be negative. Sugarcane works well as a bifuel though - Unlike corn you get six times as much energy as you put in.
  • Durwood M. Dugger on July 22 2012 said:
    "Feedtheworld" your information is more than a decade old - because that's when the US ceased being and a major net exporter of phosphates and fertilizers. According to 2011 USDA report refd. below and in Chris's article the US now imports 54% of it's phosphates. Perhaps you should read some those "glory seeking" academics articles and references and up date your perspective.

    Everyone can make their own decision, but it helps to be informed as best you can. Here are some of the articles that shaped our perspectives to date and I would draw your attention particular to Dr. Dana Cordell's explanation of peak phosphate issues (http://www.mdpi.com/2071-1050/3/10/2027/):

    Algae Biofuel Economics -


    (www.liv.ac.uk/~jan/teaching/References/Walker 2009.PDF)




    Algae Production Realities -



    (www.liv.ac.uk/~jan/teaching/References/Walker 2009.PDF)


    Sustainability Issues - Peak Petroleum



    Sustainability Issues - Peak Phosphates -













    Environmental Issues


  • Durwood M. Dugger on July 22 2012 said:
    FTW, one more flaw in your claims of the peak phosphate myth - the USGS estimates of world phosphate reserves has little to no "ground-truthed" scientific basis for either quantity and most especially the economic quality of the reserves they list, but relies on host country information and or fertilizer companies who use their "reserve estimates" as bankable assets and are highly likely to exaggerate them - just like Saudi Arabia and other OPEC countries exaggerates the quality and quantity of its oil reserves. You should also consider that as of 2002 China ceased all exports of their own phosphates - not likely because they weren't interested in the money, but rather they realize their strategic vulnerability in doing so. Something that never occurred to our scientific illiterate political leadership.
  • Tomi Luoma on September 10 2012 said:
    The global phosphate demand should not be projected that way decades in to the future, because if the price of phosphate rises to indicate resource scarcity, and peak phosphorus is about resource scarcity, then the consumption and thus demand of phosphate will decline. We have high prices to actually limit the overuse of scarce resources. However, high price of phosphate could cause problems, but one should say change. There are not substitutes for phosphorus, but...

    Of course, non-food uses of phosphate would be the first to be minimized to save phosphate for food production that is more important: use of phosphate to produce biofuels would be on the line as unnecessary, but also animal feed production. Today, the majority of grains, soybeans and oil cakes are used as animal feed. If we want to conserve phosphate, vegetarian diets with wild fish and shrimps would reduce the demand and consumption of phosphate considerably. Waste will be minimized...

    Also, mineral resources are always reported with some classification, and the estimate of phosphate resources is most likely the "phosphate resources that are economically recoverable with the current price". However, when the price of phosphate rises, it is expected that the economically recoverable resources will grow as rocks with poorer concentration of phosphate will be utilized. Poorer phosphate rocks will suddenly become economically profitable to mine. More resources will be added...

    Also, nutrient recycling can also be utilized at waste water treatment plants if it is economically viable and this reduces the demand for mined phosphate. As the final thing I will say, that the Earth contains a lot of phosphorus and the average concentration in rocks in general is 0.1 percent, and there must be a lot of deposits that have a higher concentration. It depends on the price of phosphate and the cost of production how much phosphate resources there will be that are economically recoverable. If fusion energy becomes a reality in the middle of this century, the the cost of production will plummet and we will have almost limitless phosphate resources.

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