Organic Farming Reliant on Synthetic Nitrogen

A number of studies have recently suggested that organic farming better addresses issues related to climate change than non-organic farming. Many of the reported climate change advantages of organic farming flow from its prohibition of synthetic fertilizers and exclusive use of organic fertilizers. In the debate over the future of agriculture, organic food proponents have been using these results to support their arguments. One such recent statement is found in the Organic Farming Research Foundation’s August 2012 publication Organic Farming for Health and Prosperity which states “…organic farming has been shown to effectively mitigate climate change by increasing carbon sequestration in the soil, reducing greenhouse gas release and consuming less fossil fuel.” In comparison to non-organic farms, most of the climate change mitigation benefits of organic farms “were due to the high energy demand and emissions associated with the production of synthetic fertilizers used in the non-organic system.” Since organic farming uses organic sources of plant nutrients, like animal manure or fish byproducts, it disassociates itself from the energy inputs and greenhouse gas production associated with synthetic fertilizer production, or does it?

I assert that organic farming, as it is practiced now in the U.S, is largely reliant on the very synthetic fertilizers and the confined animal feeding operations that it prohibits. The link in this reliance is animal manure and the key nutrient is nitrogen. Nitrogen is the most limiting nutrient for global food production, and therefore the most important. Although the air is full of nitrogen, it is unavailable to plants until it is “fixed” in a form available to plants, such as ammonia. Nitrogen can be either biologically fixed or chemically fixed. Biological fixation occurs in legume plants and is the avowed source of nitrogen in organic farming. Chemical fixation of nitrogen is done through the Haber-Bosch process, which currently uses natural gas to produce nitrogen fertilizer. This energy intensive process is one of the main sources of greenhouse gas emissions associated with non-organic farming.

To see the reliance of U.S. organic agriculture on this chemical fixation of nitrogen fertilizer, one has only to follow the element back to its source and then determine if it was fixed biologically or chemically. The basic steps going backwards are manure>animal>feed>crop or grass>soil>fertilizer or soil nitrogen. Most of the nitrogen is conserved in this process (60% of the nitrogen in dairy cow feed ends up in the manure), going from soil through crop and animal to the manure. So the source of the nitrogen in the manure is determined by the source of fertility for the crops used to feed the livestock. Since the nitrogen in the manure from non-organic farms comes mainly from synthetic nitrogen fertilizer, it is mostly fixed chemically. The route that the nitrogen takes between being chemically fixed and ending up in the manure does not change this. Chemically fixed nitrogen processed through livestock is still chemically fixed.

The problem occurs because the USDA organic standards designate manure, whether from organic or non-organic livestock production, as an allowed “organic” fertilizer, presumably because it came from a living organism. This means that, in the U.S., organic farmers are permitted to use manure from non-organic feedlots, chicken houses, pig barns, and fish farms. Often, the manure is processed (composted, pelleted, etc.) between the non-organic source and the organic farm, but this does not change the source of the nitrogen in the final product. Furthermore, most of this manure comes from confined animal feeding operations, which are prohibited under organic standards. These operations benefit organic farms by concentrating the manure, allowing it to be more easily collected than it is in grazing systems. The manure is then used on many organic farms where it is often their main source of nitrogen.

This system allows organic proponents to claim that they are free from all the downsides of synthetic fertilizer production while also claiming all the benefits of using manure for their system. However, this is clearly not accurate. As long as organic farms are allowed to use manure from non-organic farms, they are reliant on chemically fixed nitrogen.

Some may object that I am ignoring the on-farm fixation of nitrogen by legumes. While it is true that some organic farmers try to produce much of their nitrogen in this manner, I maintain that most of the large organic farms that make up the majority of organic acres and production, do not utilize biological nitrogen fixation to any significant extent. Furthermore, even if the manure being imported from non-organic farms contains mostly legume-fixed nitrogen, this nitrogen is often dependent on synthetic fertilizers supplying phosphorus and potassium to the legumes, without which they would fix much less nitrogen.

Ultimately, what is at stake here is the choice of what path agriculture takes in the future. If we are to make good decisions about the tradeoffs of various farming systems for dealing with climate change, increased global food requirements, and energy needs, then we need to understand the complete life-cycle impacts of each system. For true accounting in energy comparisons, sustainability comparisons, discussions of the productivity of organic agriculture, and the possible future paths of agriculture, knowing that U.S. organic agriculture is reliant on the use of synthetic fertilizers (especially nitrogen) by non-organic farmers is important.

There is a remedy to this. Organic marketers and proponents could acknowledge that they too have challenges in addressing climate change. A step in this direction would to change the USDA Organic rules to prohibit the use of manure from non-organic farms. If organic farms were to use only manure that came only from organic livestock production, which itself relies exclusively organic feeds, this would close the organic nutrient loop. The organic food industry would then be able to support their claims of addressing climate change.


Here is research on this topic from France,

Nowak, B., Nesme, T., David, C., & Pellerin, S. (2013). To what extent does organic farming rely on nutrient inflows from conventional farming? Environmental Research Letters, 8(4), 044045.


15 comments on "Organic Farming Reliant on Synthetic Nitrogen"
  1. So what happens when there is no synthetic n available because we have used up all of the oil/ natural gas? Legumes and organic manure appear to be the only options. Shouldn’t we be focusing some research towards this inevitability?

    1. Maurice, ultimately you have identified the key options for a sustainable nitrogen supply — we need improved our capacity to fix and re-cycle nitrogen biologically. Plant-based legumes are currently the most likely strategy for commercially viable biological N fixation on a grand scale, though in the long-term there is also the potential for microbial N fixation with naturally occurring microbes. Most of our prior analysis indicates that biologically fixing N “in place” where the crop can use it is the most energy efficient, climate-friendly strategy. Furthermore, Andy himself has extensively explored the potential for using legumes in his cover cropping systems.

      Recycling livestock manures and other organically derived wastes is also likely part of the solution to “keeping the N fixed” and usable by crops, but as Andy points out there are complicating sustainability factors that need to be understood. Otherwise, we’ll end up using more energy to “recycle” biologically-fixed N than to chemically “fix” new N from the atmosphere.

      As you are well-aware from your long participation with the Center, sustainable nitrogen supply is probably the single most substantive area of historical research investment by CSANR. In my opinion, this is one of the greatest obstacles to a truly sustainable global [or local] food supply – and perhaps the most challenging to overcome. There have been some extremely creative strategies developed by many scientists within WSU that I think are moving us down the path toward a more sustainable N supply for all of the types of cropping systems in Washington.

      1. Haber-Bosch is sustainable, if not organic. All you need to do is replace fossil-fuel-supplied hydrogen with sustainably-powered electrolysis.

  2. thanks for the informative post,i find it very helpful and useful.thanks for sharing about health.

  3. Andrew, I know this thread is old, but I wanted to say you make very legitimate points. The other issue is that in the process of composting the manure to make it safer for use on food crops, there are surprisingly large emissions of methane. Just because the intention is for the process to be aerobic, there are clearly anaerobic sites. This means that the carbon footprint of a crop getting its N via compost is more than 10x that of synthetic N. Also there are several technologies under development to do small scale Haber-Bosch using wind, solar or other energy sources. Farmers could then make their own carbon-neutral nitrogen fertilizer.

  4. My issue with the use of non-organic manure lies more in the presence of growth hormones, foot-bath residues (and other anti-fungal chemicals), residual pesticides from the feed, and antibiotics which are routinely added to help cows digest corn-based feed. Has anyone tested for these in “organic animal manure fed crops” vs conventional? Regardless of the answer, I still think it is of utmost importance to close the cycle and use as much of the manure as we can… at least it is a step in the right direction for now. Thank you for a very interesting article!

    1. Alexandra, I am not sure of the amount of the materials that you mention that make it into the manure. Even if they do, it is not likely (perhaps impossible, at least with some of them) that they would then move into the crop grown on the manured soil.

  5. As an organic crop consultant working with large farms in the Columbia Basin I have first hand experience with the REALITY of actually making a living at this rather than fantasizing about some small farm Nirvana where everyone grows their own food on 40 acres.

    So what you are suggesting is that we let all that conventional manure go to waste and not recycle it? Brilliant.

    How about this, we allow Bosch-Haber into Organics so that we can continue to maximize efficiencies that are already established in the agricultural industry.

    Give Organics access to Urea and the N problem goes away. We are talking about the process of heating the chemicals to 600 degrees Celsius (Haber-Bosch) and not the actual natural gas because it IS “of the Earth”. Furthermore, the NOP already allows for some petroleum products so the argument against Natural Gas because it is petro based is nullified.

    I believe more conventional farms would convert to Organics much more quickly if the NOP opened regulations to Urea.

    What you propose won’t happen in my lifetime but a simple adjustment to the NOP allowing Urea has an immediate impact for Organic growers – NOW.

    This single change to the NOP rules would encourage less conventional pesticides and herbicides being used in the environment – NOW.

    There is a disconnect between the fantasicm of organic truck farms selling their wares at the local farmer’s market and the realities of making a profit on a 1,000 acre organic farm.

    The number one reason people choose to pay extra for organic produce over conventional is the lack of pesticides and herbicides.

    Few consumers even care about Haber-Bosch.

    BTW, Alexandra Holland’s concerns about chemicals in conventional dairies and stockyards is valid.

    1. Mike, thanks for the comments. I am not at all suggesting that we let manure go to waste. In fact, I would think that a majority of the manure produced in the county is used by conventional farms. This is a good thing, and also a good thing that manure is used on organic farms. The only thing I was pointing out is that the nutrients in much of the manure going to organic farms comes from synthetic fertilizers.

      Although urea is not the direct result of the Haber-Bosch process, urea is produced from ammonia which does come from the Haber-Bosch process. So urea is linked to Haber-Bosch unless you come up with another source of ammonia, at least as far as I know.

      You may be right about few consumers caring about the Haber-Bosch process (even though 2/5 of us would not be around without it) but at least some of them prefer crops grown without synthetic fertilizers.

  6. Human sh**, now a problem, could be one solution. Two or three years in a careful (high, dry & hot) composting situation, urine separated, makes this potential polluter an excellent source of Nitrogen rich earth.

      1. Still, most of that is going to waste right now. Making more efficient use of that resource, while gradually transitioning towards biological N fixation, would help.

  7. Using human waste may sound good but it would contain a multitude of chemicals from drugs humans take – tons of estrogen, antibiotics etc. What will the plants do with that? Feed it back to us?

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