New research shows that modern farming – the kind practiced on nearly all farmland in the United States and touted around the world as the “green revolution” – destroys soil carbon. Synthetic nitrogen contributes to climate change and undermines long-term soil productivity because synthetic nitrogen breaks down organic matter faster than plant residue creates it.

In papers published in 2007 and 2009 University of Illinois researchers Richard Mulvaney, Saeed Khan, and Tim Ellsworth argue that the net effect of synthetic nitrogen use is to reduce soil’s organic matter content. They hypothesize that nitrogen fertilizer stimulates soil microbes, which then feast on organic matter. Over time, the impact of this enhanced microbial appetite outweighs the benefits of the additional crop residue left behind as a result of increased fertilization.

Tom Philpot summarizes their findings in a post at Grist:

And their analysis gets more alarming. Synthetic nitrogen use, they argue, creates a kind of treadmill effect. As organic matter dissipates, soil’s ability to store organic nitrogen declines. A large amount of nitrogen then leeches away, fouling ground water in the form of nitrates, and entering the atmosphere as nitrous oxide (N2O), a greenhouse gas with some 300 times the heat-trapping power of carbon dioxide. In turn, with its ability to store organic nitrogen compromised, only one thing can help heavily fertilized farmland keep cranking out monster yields: more additions of synthetic N.

The loss of organic matter has other ill effects, the researchers say. Injured soil becomes prone to compaction, which makes it vulnerable to runoff and erosion and limits the growth of stabilizing plant roots. Worse yet, soil has a harder time holding water, making it ever more reliant on irrigation. As water becomes scarcer, this consequence of widespread synthetic N use will become more and more challenging.

In short, “the soil is bleeding,” Mulvaney told me in an interview.

The idea that synthetic fertilizers destroy soil health is not new. Philpot quotes from the book The Soil and Health by British agronomist Sir Albert Howard, a touchstone of organic farming first published in 1947:

The use of artificial manure, particularly [synthetic nitrogen] … does untold harm. The presence of additional combined nitrogen in an easily assimilable form stimulates the growth of fungi and other organisms which, in the search for organic matter needed for energy and for building up microbial tissue, use up first the reserve of soil hummus and then the more resistant organic matter which cements soil particles.

A recent report by UNEP and the UN Conference on Trade and Development is consistent with the researchers’ results, finding that in Africa yields had more than doubled where organic, or near-organic practices had been used, with yields jumping 128% in east Africa. The study found that organic practices outperformed traditional methods and chemical-intensive conventional farming and produced environmental benefits such as improved soil fertility, better retention of water and resistance to drought.