Interview with David Montgomery, Champion of Soil Health

NB: Can you explain the nitrogen/carbon oxidation nexus?

DM: A big part of why nitrogen draws down carbon is the ratio of C to N in living things. If you are going to get that nitrogen into a living organism you need a lot of carbon to pair it with.  So if you are fertilizing soil in a way where you have either microbial growth or fungal growth thats unlimited in terms of nitrogen its going to gobble up a lot of carbon. There are different ways to get the carbon into the soil... the microbial degradation of organic matter basically turns it into carbon rich compounds that stick around better....A lot of the soil organic matter is actually microbial in origin, so you can think of the organic matter wether its being added by roots sloughing off or pushing out exudates as a great way to feed microbes and grow fungi in the soil, or wether its cattle trampling and merging that down into the soil where microbes can get at it, there are different ways to do it or if its just planting legumes that can partner with microbes to get enough out of the atmosphere to fertilize a crop. I was impressed with the magnitude of N fixation that can happen when you really promote the development of the microbiota that are N fixers. 

NB: So its harder to be carbon regenerative in tillage agriculture

DM: The combination of tillage and a lot of nitrogen application wherever you got the nitrogen that by itself is a recipe for burning up organic matter and drawing down fertility, no-till is one of those things where if you just study it by itself it can either build organic matter or it can do very little or it can even lose organic matter,... the combination of three practices of no-tillage, planting cover crops/ keeping the ground covered and having a diverse rotation not just growing the same things over and over, the combination of those three elements is what really builds organic matter and fertility. 

NB: How is soil decarbonized?

DM: If you don't keep recycling the living matter, if you're fertilizing and plowing you're getting carbon into the system and then venting it, .... if you don't plow you can build up your reservoir and then cycle it... Coupled with plow based agriculture We've demonstrated that we've lost about half the organic matter in n american soils.

NB: How much anthropogenic carbon has come from burning fossil fuels versus soil oxidation

DM: There was a study done in 1978 by Minze Stuiver, the trend is pretty clear... Minze Stuiver looked at carbon isotopes and found that about a third of the CO2 that had been added to the atmosphere since the industrial revolution did not come from fossils fuels but came from soil organic matter mostly from plowing up the american midwest and western russia, at that point it was about a third, I haven't seen an update quite like that but my guess is that its somewhere in that same ballpark, in other words its a lot, and that is carbon that in principle could be put back in the soil were we to rebuild soil organic matter on our agricultural lands. A farmer in Ohio that i visited essentially weaned himself off nitrogen and herbicides he was using about 10% of what his neighbors were using, he cut his costs by 90%, he ran me through the farm economics on a per acre basis, his neighbors were losing... about a $100/acre , meanwhile he  has rebuilt soil  organic matter levels from about 1/2 percent he started to around 5-10%,  values comparable to what the original soil carbon content, .. and he's making $400/acre.... so, Instead of subsidizing destructive conventional practices we ought to be subsidizing regenerative practices that are better for the farmers, better for the soil life, better for the pollinators and the birds that visit and arguably better for the food we we eat.

NB: Thoughts on soil testing?

DM: Conventional soil tests will simply look at the amount of plant available nitrogen or phosphorous or whatever and thats a narrow lens with which to look at it because that assumes you cant change whats in the soil, particularly for elements other than nitrogen. Whats available in the soil in the soil is enough to grow plants for centuries , the problem is getting it out of the mineral particles in the soil, the rock fragments , the clay minerals and getting it into forms the plants can take up, thats the job of microbes thats what fungi do thats what bacteria so if you just take a random soil test and you look at the available nitrogen the available phosphorous what thats telling you is what the plants can take up out of that soil without any benefit or assistance from microbial life but we know there are microbes that can fix nitrogen thats 19th century science that predates Haber-bosch, we also know that fungi will scavenge certain nutrients like phosphorous from rocks and trade them to plants but none of that phosphorous that the fungi can scavenge and none of the nitrogen that microbes can fix out of the atmosphere of which theres plenty, were bathed in it what.. 79% of our atmosphere is nitrogen, the trick with nitrogen is getting it out of our atmosphere, Haber-bosch can do that, but half the synthetic nitrogen we apply to are fields never make it into the plant and because were applying it in a soluble form, it runs off it gets int groundwater, it gets into streams, its whats causing the great dead zone in the gulf of Mexico and causing the city of des moines to sue the local farmers for polluting the water supply.... but if instead you think of nitrogen fixation from microbes as putting nitrogen from the atmosphere into the roots of plants right where you need it, that stuff doesn't run off it tends to get used......, if then you plant a cover crop that circulates nitrogen, its available to plants as that material decays, its a steady supply,. Its even more important for the micro nutrients which are critical for plant health, so in terms of soil tests one of the things that I did not know as a geologist, going and talking to farmers and agronomists, realizing the distinction between whats readily plant available and whats there in the soil ready to be unlocked by the microbes in the soil that can get them to the plants , again thats where biology in the soil becomes so central and important to fertility because if you just look at it through the lens of readily available chemistry it might look like you really need to add a ton of nitrogen and phosphorous to grow something, then you go and visit some of these farmers that are instead rebuilding the organic matter to feed the microbes that then unlock the sources of phosphorous and provide the n fixation in the soil and their able to grow comparable crops with hardly any fertilizer relative to what their neighbors are using makes you wonder wether we've missed a piece of the equation and thats the biology.

NB: Revolution is a coming!

DM: Thats where the title of my new book, "growing a revolution" is as much about how we think about soil as it is about is about how we farm, the philosophy that underpins how we look at soil. wether you view it as a chemical reservoir to  be topped up with the ingredients you need to grow plants or wether you view it as an ecological system where you r trying to cultivate the species you would like to be productive and then increasing their cycling so you can shave a little off the top as a farmer, thats a whole different philosophy of soil. Modern farming has basically created large fields of the same plant that are stressed because they are over-provided with major elements and under provided with micro nutrients and we have increased our pest and pathogen problems and that creates a need for insecticides and...

NB: Chemical dependency...

DM: Yea, its a recipe for chemical dependency, that's it exactly.

NB: What are the scenarios where the farmers you studied need to spray herbicides

DM: We live in a society that is fairly polarized in terms of political views...there is a significant proportion who don't want to be doing the hippie farming thing, but they are perfectly happen not spending money on pesticides and fertilizers... one farmer said I haven't actually used herbicides in 3 years, he hasn't needed it but he wants to be able to just in case.... Why did farmers till in the first place, weed control! And why are herbicides particularly glyphosate are good at weed control.. why because it kills everything unless it has a gene in it that has been modified to let it live through glyphosate. The development of gmo crops helped the adoption of no till because it made weed control easy. Now there are other ways to control weeds that don't involve herbicide. A number of the farmers I visited with who were conventional farmers had been experimenting with different cover crops to outcompete the weeds, instead of the kill everything model....they basically went to the "lets outcompete the weeds" model so what you do is as you plant your primary crop you plant a cover crop either shortly after or along with it that will come in under your main crop and basically shade out the weeds and outcompete them. If your cover crop isn't harvested but you knock it down so it rots... it keeps the weeds out and its drawing nutrients into biological play in organic matter, then you let that organic matter rot. Theres this great invention called a crimper roller that is a crimper roller that goes along with no-yill planting that could completely replace the herbicide dependence of some of the no till farmers and the big criticism you'll often hear is that they use a lot of herbicide, but its not necessary, thats a practice, its a choice..... so a roller crimper is basically a steamroller drum with metal chevrons on it that you roll over and crush the cover crop, you put one on the front end of your no till planter, crush the cover crop and plant through it, what it does is create an organic mulch, and that mulch both keeps moisture in the soil its made out of organic matter that will rot and provide nutrients back into the soil, and it provides really good weed control. And you're basically putting this organic mulch down but you've just planted your seed so they have the head start, the first thing that comes is your crop and the weeds are suppressed because they take longer to come in because that mulch is keeping them down.. so the philosophy these farmers have adopted is one of ecological wisdom to replace one of sheer chemical brute force.

NB: Nixon passed the clean water act, the endangered species act, Is it possible to think that under a Trump we could see a carbon farming act?

DM: I think we have a real opportunity in terms of the farm act of 2018, trying to prioritize things that rebuild soil health, I honestly think this is where red states and blue states can come together.... building soil health is good for american farmers... a side benefit would be rebuilding soil carbon. Even some of the big agri-chemical giants are starting to see the long term wisdom of going towards more regenerative practices, some are switching up their product mixes , some are trying to get into designing microbes that fix nitrogen..., there are all kinds of arguments you could have about genetic engineering and the wisdom of wether or not you put a gene in a microbe will it stay put, I mean horizontal gene transfer is not gonna let that happen. (laughs) But those are all different arguments than wether or not we should be embarking on a national infrastructure project to rebuild soil organic matter. 

NB: Is there a danger that all this innovation might be guarded carefully as intellectual property?

DM: One of the things that impressed me about all the farmers that i visited None of them suffered that problem, they all wanted to share and talk about what they had done. They were genuinely interested in spreading something that was good for people and the world. 

-Nik Bertulis

I met with David, my favorite soil writer, at a small coffeshop near Green Lake in Seattle on May 7th of this year to discuss the release of his new book "Growing a Revolution."