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“Devil in the Details”: P demand and biofuels

April 13, 2010

Today’s issue of BioScience (link) includes a commentary by Werner Flueck (National Council for Scientific Research, Argentina Institute of Natural Resources Analysis) noting that a strategy for crop-based biofuels involving things like switchgrass and such is unsustainable, as it will place elevated demands on limited P reserves.  In reply, Tom Simpson (Water Stewardship, Inc.)  notes that crop biofuels will rely on gasification and other processes which permit P recycling.  Unfortunately, that would only recover the P from the harvested crop itself.  As we know from study of intensive food crop agriculture, the bulk of P is lost via soil erosion and NOT in the harvest.  So, this is an incomplete solution.  Simpson also notes, correctly, that most agricultural soils in the USA and elsewhere in the developed world are saturated with P and thus biofuel crops can “mine” that P.  This is also true, but for how long?  Seems like an open research question.  Can anyone reading this offer an educated guess?

4 Comments leave one →
  1. April 16, 2010 8:54 pm

    Hi Jim,

    Great website you’ve got here. Thanks for the shout-out regarding my article on Seeking Alpha. I got a laugh when you described me as an ‘investment analyst’, I am but a student!

    According to the Mosaic 2009 annual report (fertilizer company, link here: “Crop nutrient use today contributes 40% to 60% of the world’s crop yield.”

    Also regarding phosphorous application:

    “When a farmer decides to reduce or forego nutrient applications, how long before there is an effect on yield?

    The level of yield at risk depends on how well the farmer has cared for the soil in the past. Some farmers apply extra amounts of phosphorous and potassium every season, and this buildup will last a season or two. But with every harvest the soil is further depleted of nutrients. Sooner or later, a properly balanced blend of nutrients must be applied in order to restore yields to optimal levels.

    Is it possible to quantify the effect on yield when nutrients are not applied?

    Thanks to years of study on research plots we have an understanding of the critical level of phosphorous and potassium necessary to provide optimal soil conditions. A field testing low-to-medium phosphorous levels would be expected to yield only 80% of a comparable field that was above the critical level.”

    So it seems you can mine the field for max 3 years before seeing about 1/5 decrease in yield, and if you don’t apply after that, I imagine the yield keeps going down. Doesn’t sound sustainable to me! As you state, most phosphorous is lost via erosion and other losses. According to Figure 11 in my article (adapted from Dana Cardell), less than half the applied P from phosphate rocks is in the harvested crops.

    One thing I’m curious about is whether any of the P reacts in the gasification process and becomes bio-unavailable? Is any P lost in the process?

    • April 17, 2010 5:44 pm

      “I got a laugh when you described me as an ‘investment analyst’, I am but a student!”

      I guess I said that based on the web site I found you on. You should be more careful about who you hang out with!

      As for P recovery from the leftovers from biofuel gasification, here we need a chemist to help us out. I can’t say I know what compounds with which PO4 will be complexed after gasification. Thus the leftovers might need various kinds of chemical treatment to separate the phosphate and get it into a form suitable for fertilizer use. This is why we need “all hands on deck” for this P sustainability issue. Anyway, the P won’t be “lost” during gasification. This is the great thing about chemical elements – they last forever! So, if we can just be more careful about letting them leak out of our hands (and out into great brown and blue yonder of lake, river, and ocean sediments), we can have a sustainable system.

      I hope you’ll “stay tuned” to our Sustainable P Initiative ( as we roll our efforts out. We are in close contact with Dana Cordell and Stuart White etc, and hope to contribute to networking all those interested in P sustainability. Look for a piece in Foreign Policy magazine (online) on Earth Day.

  2. April 27, 2010 8:49 pm

    Use of liquid fertilizers give higher transport of phosphorus to the plant leaving less to soil erosion, surface and groundwater pollution. This is part of the phosphorus sustainability solution. The research group at the University of Adelaide in Austrailia has been doing great work in characterizing and quantifying this advantage for some time now.

  3. April 27, 2010 10:08 pm

    Yes indeed. We can be much more efficient in how P is applied to fields so that most of it ends up in the crop and not in the groundwater or surface water…

    Please keep in touch and watch for details of the upcoming Sustainable Phosphorus Summit in February 2011.

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