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Always Follow the Nitrogen

Posted by Andrew McGuire | December 7, 2021

“Follow the money” is a reliable tactic for figuring out people’s actions. Money is scarce, people want it, and do stuff with it. For plants, what works is “follow the nitrogen.” Nitrogen is scarce, plants and other organisms need it, and when they get it, the results are remarkable. Here are some examples of how following the nitrogen is useful.

Nitrogen symbol from the periodic table.
“What makes N different is the absence of a mineral-bound, weatherable N pool in most soils.” (Robertson and Vitousek, 2009)

As I covered in my last post, lack of available nitrogen often limits the populations of plant-eating insects. Most of them die in their first few hours or days of life for lack of protein. But when they do find sufficient nitrogen, their populations can explode. This is the life and death power of nitrogen, and not just for insects.

I’ve been told that an agronomist is someone who is continually amazed by plant’s response to nitrogen. Well, YES, because it is amazing. Behold the power of nitrogen: these researchers measured 89% more yield, 61% more root carbon, and 187% more soil carbon (organic matter) storage from a moderate addition of nitrogen fertilizer (Yang et al., 2018). And this was with high-diversity grasslands. It’s no wonder we agronomists have a nitrogen fixation.

There are thousands of more examples of the power of nitrogen to increase production of crops. This is why following the N is crucial to interpreting crop studies. If non-N factors are the focus, then nitrogen levels should be equal. This is hard to do when using both organic and synthetic N sources. If nitrogen is the focus, or even when it is not but there are differences in N rates or availability, then the power of N can be seen through reliable, statistically significant differences between treatments, often hiding effects of other less powerful factors. A good starting question when looking at any agricultural field study is, “Can the results be explained by nitrogen differences?”

Three men standing in a wheat field.
New research suggests that the species Triticum aestivum has entered a symbiotic relationship with the species Homo sapiens. The latter have a unique nitrogen-fixing process which provides N to the Triticum in exchange for an annual supply of grain for food. Photo by Scott Bauer, USDA Agricultural Research Service.

Because of nitrogen’s reliable and remarkable effects on insects, plants, microbes, and just about every other organism, following the N is a good strategy for evaluating claims. Consider the claims that soil carbon storage can reduce CO2 levels or even reverse climate change. This group of researchers followed the nitrogen and concluded in their paper, “Sequestering Soil Organic Carbon: A Nitrogen Dilemma”, that storage of C in the soil is limited by nitrogen availability (van Groenigen et al., 2017). Why? Because soil C can be traced back to plant C and plants need nitrogen to produce well. To put more C into the soil, we will also need more N.

Another example related to soil carbon storage. In a study of carbon stored after a “thin layer of compost was applied” to rangeland, researchers found that above- and below-ground productivity increased resulting in a carbon storage increase, beyond the carbon added by the compost (Ryals and Silver, 2013). This is great, right? “Do the math” is a close companion of “Follow the nitrogen” However, when I did the math to figure out the amount of compost applied in units that people in agriculture can relate to, I found they applied 31 dry tons per acre. It may have looked like a thin layer, but this is a lot of compost. Doing the math on the nitrogen, I found they applied 1150 lbs. of N per acre! Despite barely mentioning nitrogen in their paper, this amount of nitrogen applied to unmanaged rangeland is the most likely cause of stimulated plant productivity and the resulting increase in stored carbon.

John @kowalchukfarms1 knows the importance of nitrogen. (Used with permission)

The nitrogen in soil organic matter also given me a handy way to evaluate claims made about the results of regenerative agriculture practices. Here, by following the nitrogen, I found that the claim of building remarkably high soil organic matter levels required a large amount of nitrogen that could not be accounted for and therefore requires more evidence or a different explanation.

Even claims not related to agriculture can be evaluated by following the nitrogen. A headline declares, NASA’s idea for making food from thin air just became a reality — it could feed billions. OK, but food, as we saw with the herbivores, requires some nitrogen in the form of protein so we can build muscle. Where does the protein come from here? Do they grab it from the air as done with the Haber-Bosch process that produces synthetic fertilizers? Or do they use some form of biological nitrogen fixation, as occurs in the nodules of legume roots? I followed the story back to the company’s website which, with a little digging, revealed that the “nutrients and vitamins” of the article includes a lot of synthetic nitrogen (ammonia) to get the 50% protein. So this food is not “free from agricultural limitations” as their marketing suggests, but shares a need for synthetic N.

Finally, following the nitrogen often means figuring out where the N comes from. Organic sources of nitrogen are often viewed as superior to synthetic sources because they are produced naturally. When I took a look at the original source of nitrogen in most of the organic amendments used on US organic farms, I found that it was synthetic nitrogen. Conventional grain, produced with synthetic N fertilizer, fed to livestock, converted to organic manure, is then composted and spread on organic farms. “Dirty” N is laundered through livestock to become clean, green-N for organic marketing purposes. Others have found the same (Nowak et al., 2013).

I could go on and on… this tactic has always served me well. Even when nitrogen is not the main factor, knowing about it helps in understanding other factors. Whether you are looking at crop responses, pests, or soil practices, I hope I have convinced you that it is always useful to “Follow the Nitrogen.”

References

  • van Groenigen, J.W., C. van Kessel, B.A. Hungate, O. Oenema, D.S. Powlson, et al. 2017. Sequestering Soil Organic Carbon: A Nitrogen Dilemma. Environmental Science & Technology 51(9): 4738–4739. doi: 10.1021/acs.est.7b01427.
  • Nowak, B., T. Nesme, C. David, and S. Pellerin. 2013. To what extent does organic farming rely on nutrient inflows from conventional farming? Environ. Res. Lett. 8(4): 044045. doi: 10.1088/1748-9326/8/4/044045.
  • Robertson, G.P., and P.M. Vitousek. 2009. Nitrogen in Agriculture: Balancing the Cost of an Essential Resource. Annual Review of Environment and Resources 34(1): 97–125. doi: 10.1146/annurev.environ.032108.105046.
  • Ryals, R., and W.L. Silver. 2013. Effects of organic matter amendments on net primary productivity and greenhouse gas emissions in annual grasslands. Ecological Applications 23(1): 46–59. doi: 10.1890/12-0620.1.
  • Yang, Y., D. Tilman, C. Lehman, and J.J. Trost. 2018. Sustainable intensification of high-diversity biomass production for optimal biofuel benefits. Nat Sustain 1(11): 686–692. doi: 10.1038/s41893-018-0166-1.

5 thoughts on "Always Follow the Nitrogen"

  1. Tony says:

    Thanks for the N-laundering acknowledgement. Following the N is very instructive for realistic examination of most “organic” enterprises. Following the pesticides and meds is similarly so, in that they enable the N-laundering so important to most organic enterprises. Productive use of wastes is awesome, so is a realistic grasp of the organic label- not to mention C sequestration strategies. Great post as usual.

  2. Bryant Mason says:

    Great article. That said, I disagree with your comment: “Organic sources of nitrogen are often viewed as superior to synthetic sources because they are produced naturally.” I believe they are superior because of the higher C:N, reducing organic matter loss that can happen with a heavy application of synthetic N.

    1. Andrew McGuire says:

      Superior or inferior depends on your goals and system. There are always tradeoffs. It is more difficult to know just how much N will be available from an organic source than an synthetic source. And if you need a quick application, say for grain protein, synthetic N is the better option. Ease of application, cost, there are lots of factors to consider…

  3. Steve Neason says:

    You wrote:

    “Conventional grain, produced with synthetic N fertilizer, fed to livestock, converted to organic manure, is then composted and spread on organic farms.”

    That is one of the reasons we won’t participate in the “organic certification” scam on our farm. The organic concept has been captured by industry and converted to nothing more than a marketing term.

    We carefully source all our nutrient needs to avoid the use of synthetics and fossil fuels wherever possible. Heavy reliance on synthetics and fossil fuels is not farming, it is mining.

  4. Eric Brennan says:

    Thanks for another interesting and thoughtful article Andy. You make many excellent points. Thanks for highlighting the Nowak et al. paper on synthetic nitrogen moving into organic systems. This is an issue that many people often overlook. Here’s a link to my video that describes issue in organic vegetable production. Brennan E.B. 2016. Sustainability problems with ‘repackaged’ synthetic nitrogen in organic agriculture. http://www.youtube.com/watch?v=3GjbnchPhl8

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