Compost and Nitrogen: Heroic Partners or Sneaky Collaborators in Pollution?

Since the publication of our first issue, which examined the meaning and art of sustainable farming (in essence, its craftsmanship), we’ve received an outpouring of responses. The vast majority have been positive, expressing appreciation for the unusual depth and complexity in our reporting. However, one of the applauders, a veteran organic farmer in California named Tom Willey (who we had interviewed at length, and quoted in our lead story, “The Drought Fighter”) took exception to a key sentence in that story. We invited him to expand on his criticism, which he did in two columns for his farm newsletter. The essay below is an edited compilation of those two columns:

The recent long read on Singing Frogs Farm’s Paul and Elizabeth Kaiser by Todd Oppenheimer indicts compost-loving organic farmers as being among California’s “worst nitrate polluters.” In my view — based on the literature that I have read, and my 40 years in farming — this makes little sense. Composting, which is the controlled decomposition of plant and other organic materials by a multitude of microbes, is arguably nature’s wise design to conserve and recycle scarce nitrogen resources. When the composting process is complete, it renders nitrogen less likely to pollute.

To appreciate this claim, it’s important to understand nitrogen’s place in our cosmology, and its curious history. Nitrogen is one of the most mysterious constituents of our big bang universe. Earth’s most abundant pure element, nitrogen, is the backbone of DNA / RNA blueprints, amino acids and proteins. Yet it paradoxically makes itself scarce. The air we breathe is 78% nitrogen, but in an inert gaseous form that cannot be woven into life’s lattice work. Only after an immensely powerful attraction between twin nitrogen atoms is cloven at great energy expense does this element become reactive with unlike chemicals to blend into life’s soup. Since time immemorial, such molecule splitting was the exclusive domain of lightning and extremely specialized soil bacteria.

Over those eons, stingy nature ordered its dynamic duo to convert (or ‘fix,’ as chemists put it) into life-available form barely one percent of Earth’s atmospheric nitrogen. Crop cultivation, therefore, is in large part nitrogen management — an art practiced from agriculture’s dawn until 1772, at which point this most limiting element to plant growth was discovered by humans to exist. Until then, farmers simply noticed that crops grew better after electrical storms; they also certainly observed that plant growth was enhanced wherever animal manure had fallen or where plant residue had rotted in place.

Then, 100 years ago, two German chemists turned nature on its head by inventing artificially synthesized nitrogen by means of heat, pressure, an iron catalyst and beaucoup energy — a feat that garnered each a Nobel Prize. Today’s Haber-Bosch industrial plants fix as much nitrogen each year as does this planet’s entire natural ecological system. Like the Sorcerer’s Apprentice, removing nature’s constraint on crop productivity induced farmers to spread nitrogen fertilizer with abandon. Yields quickly soared, world granaries overflowed, the population of better-fed humans tripled over three generations.

So why are Midwestern cities about to sue the hands that feed them? Synthetic nitrogen fertilizer is grossly inefficient. Less than half of what’s applied assimilates into targeted crops — the rest causes environmental mischief, polluting streams, lakes and municipal water supplies if applied as nitrate, or when microbial activity converts it into the more leachable nitrate form. Mature compost, however, contains only minuscule amounts of this easily leached nitrate.

Craftsmanship noted that Paul Kaiser has gathered more data on his organic methods than most farmers have, yet he still lacks a complete picture of his fertilization system. Like most of us farmers, he has no exact measure of how much nitrogen goes into his fields, and how much comes out, or in what forms.

What sort of inquiry might answer this question — for Kaiser and other farmers who use lots of compost? In other words, how can we defuse controversy over whether compost-loving organic farmers like the Kaisers and the Willeys are indeed our “worst nitrate polluters,” or responsible soil nutrient managers? One way to judge is by employing a lysimeter.

What’s that? Think underground, open-topped terrarium, buried beneath a farm soil’s growing crop. Researchers install lysimeters as catchment systems to intercept rain or irrigation water percolating through plant root zones towards an aquifer. That liquid is easily drawn off and can be accurately analyzed for nitrate and other soluble nutrients threatening water quality. Has anyone used lysimeters to compare composted crop systems to those that are chemically fertilized?

Arduous internet search turned up only two such studies, both from Europe, unsurprisingly, since that is where biological agriculture garners more respect. In the first, for each of 11 years, Austrian experimenters applied a standard chemical nitrogen dose to one plot of food crops while another treatment received compost containing four times that amount of nitrogen. Lysimetric data compiled by the Institute for Organic Research, assisted by Austrian federal scientists, came to the following conclusion: While in some years both plots lost nitrogen below the plant’s root zones, the composted soil posed no increased threat to the environment.

This long-term Austrian trial — as well as the second study, just underway in the Czech Republic — suggest a soil nutrient dynamic unique to biologically influenced systems. Raw compost ingredients must be properly blended for specific carbon to nitrogen ratios, for very particular reasons: Carbon provides energy for legions of bacterial and fungal decomposers while nitrogen builds their protein. After a fortnight of digestive frenzy plus a critical six-week curing process, compost is mature. At that stage, all of the nitrogen is sequestered into living and dead microbe bodies.

The bottom line is that soil-applied compost functions like an interest-bearing savings account, while chemical nitrogen applications approximate shopping sprees. Biological farmers expect compost deposits will convert 10% to 20% of insoluble organic nitrogen into plant-available form the first year, followed by 5% to 10% returns for years thereafter. In this dynamic soil environment, compost nitrogen continues to liberate (mineralize) nutrients through a continual process of soil organic matter decomposition. Throughout this process, invisible microbes also turn upon each other in intricate predator-prey interactions that release additional nutrients that plants can access. (For more detail, see  “The Bug Whisperer,” by Kristin Ohlson.)

Mineralized nitrogen’s fate is therefore determined entirely by farm management, which, like all politics, is local. In Singing Frogs Farm’s case, Sebastopol’s mild climate enables year-round vegetable production — and year-round compost degradation. As a result, Paul Kaiser’s quintuple crop rotation could be nicely mopping up all of the nitrogen in his compost, even though it’s applied at 60 tons per acre each year – about four times more than I put on my fields. (For proof of the efficiency potential in a system like Kaiser’s, one need only look at the research by Cornell Cooperative Extension’s Emily Cook.) In fact, Kaiser’s unusual no-till practice fosters a larger soil microbial community that can safeguard even more nitrogen. Rock throwers best grab their shovels and a lysimeter.

Since 1981, Tom Willey and his wife, Denesse, have operated T&D Willey Farms, a 75-acre certified organic farm in Madera, California. Willey has served as Slow Food USA’s governor for California’s Central Valley and on the boards of directors of the Ecological Farming Association (EFA) and California Certified Organic Farmers (CCOF). He currently serves as a Policy Advisor to The Cornucopia Institute, which monitors the integrity of the U.S.organic industry.