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 chang


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.