Soil food webs: from farm to garden?

Here’s something I’ve been meaning to write about since February, when I heard Elaine Ingham talking about soil food webs at the Canadian organic growers conference. Dr Ingham is one of the main movers and shakers behind this apparently increasingly influential perspective, which has found its way into the gardening firmament through books like Lowenfels and Lewis’s Teaming With Microbes. The idea in a nutshell is that plant/crop growth is interdependent with a complex web of small, mostly soil-living organisms. Plants exude proteins and carbohydrates into the soil, funded from their photosynthetic way of life, which provides food most importantly for bacteria and fungi, and thence to a vast array of other single- and multi-celled critters whose life and death in the soil provides the complex nutritive foundation upon which the larger organisms intelligible in the everyday human world build their lives – the trees, the shrubs, the grasses, the forbs, the birds, the mammals, the reptiles, the molluscs, the arthropods and so on.

Two main points emerge from this of relevance for farmers. The first is that despite our impressive level of human knowledge about the chemistry of soils and plants, we don’t really know exactly what our crop plants need to thrive at any given time – only the plants know that (‘know’, that is, in a biochemical sense – which brings to mind this nice article by Richard Mabey about plants as authors of their destinies in ways not always suspected by humans). So instead of fiddling about with idealised fertiliser regimens, we’d be better off just providing the plants with healthy soils teeming with life, and let the plants themselves get on with the job of self-nutrition. This is basically the familiar adage of the organic movement: feed the soil, not the plant. A further, unproven, implication is that plants which have been able to optimise their self-nutrition may better enable us, their predators, to optimise our own.

The second point concerns precisely how you ‘feed the soil’. What you don’t do, according to Dr Ingham, is add synthetic fertilisers or pesticides, because these salty additives kill soil life. Nor do you till, because this does the same – particularly in the case of delicate fungal hyphae, which are torn apart by ploughs and harrows. So instead you add compost – lots of it. That’s how you feed the soil.

Not just feed the soil, in fact, but according to Dr Ingham actually build it. She was scornful of the USDA agronomists who claim that soils form at a rate of (I think she said) one millimetre per year. She informed us that she could make a soil thirty feet deep in two days (or some such improbable amount…I forget the exact figure…), evidenced by her work to create a native Texan prairie in just one year at the gardens of the George W. Bush Presidential Library in Dallas, where her photos showed us trucks dropping off compost by the ton1. Cue astonished wows and whoops from the audience…

…and an uncontrollably arching eyebrow from me. It’s not, of course, that I question the morality of working to beautify the legacy of the USA’s 43rd president. Because, let’s face it, no amount of native Texan flora could make Mr Bush come up smelling rosy. No, it’s because…because…well, JUST WHERE THE HELL IS ALL THAT COMPOST COMING FROM? Surely from the detritus of an American agricultural civilization which, though it accumulates in centres of human population, ultimately stems directly or indirectly from its farmland. Let’s put it another way: if you put your mind and a decent number of large trucks to it, you can probably produce and spread compost several feet thick over the 13 acres of the George W. Bush Presidential Library and several other such institutions besides. What, I’d submit, you can’t do is spread it over the 900 million plus acres of farmland in the USA where I suspect the overall rate of soil formation is more likely going to approximate to that disparaged USDA figure, and then only if you’re lucky.

The implications of all this are potentially significant. First, I suppose I should pose the question as to whether Dr Ingham’s arguments are sound. There are those who would doubtless argue that farmers have been merrily tilling and spraying their fields for a long time now and nobody’s died yet – well, nobody identifiable anyway, apart perhaps from a few farmers. Personally I find it plausible that we’ll have to look after both soils and soil food webs better than we presently do if agriculture is to continue to serve humanity well long-term. And there does seem to be some evidence that repeated fertiliser and pesticide applications aren’t good for soils, but I’d be interested to hear more expert views than mine on this.

On a garden scale, I think it’d be quite easy to grow food in no-till beds nurtured by compost made on site. True, that’s partly because in a domestic growing situation people are rarely producing all their own food so there’s a net nutrient inflow – particularly in modern industrial societies awash with cheap energy and fertiliser. In a self-provisioning or ‘peasant’ situation it’d be harder, but probably still doable with careful attention to human and animal wastes, compost crops and the like. This is something I plan to start trialling soon and will hopefully be able to write about in the future with my own data to hand.

In a broadscale farming situation, though, it’s tricky to see a solution. You could go for the conventional no till approach with synthetic fertilisers and pesticides. You could go for the organic approach with clover leys and tillage. But both fall foul of Dr Ingham’s strictures. I suppose you may be able to establish some kind of permanent pasture and/or biomass crop with a cut & compost or graze & confine regimen, which enabled you to transfer nutrients to the crop. But I imagine it would be quite inefficient in terms of per hectare yields and possibly also energy inputs. Maybe organic no till methods will prove feasible, with crops established in a clover sward.

In southern England where I live, the cool, moist climate and heavy soils make for a very forgiving environment for tillage farming. The annual crops that we grow prosper in bacterially rather than fungally dominant soils, and bacteria are relatively little affected by tillage. So the system I’ve adopted has essentially been a standard organic ley and tillage one, albeit with a few closed-ish loop, no till affectations thrown in. But there are lots of good reasons to try to avoid tillage, especially if Ingham is right and you need a decent level of fungal hyphae in the soil even for annual agricultural crops to prosper. So maybe my present approach will prove unsustainable in the long run. But the George W. Bush presidential library approach is certainly unsustainable in the long run. Fitting, perhaps, for a rather unsustainable president. So are we then left only with the peasant self-provisioning option? Nurture your own soil, grow your own vegetables, compost your own excrement…oh and buy land, they’re not making it anymore, as Mark Twain had it. Or at least only at 1mm per year.

Well, that’s a familiar bottom line conclusion for me to reach. This website ain’t called ‘small farm future’ for nothing. Even so, my feeling is that Ingham’s no till, soil food web approach may be something of an ideal, and there’s room for messier compromises to be made with the world. It may be best not to till for soil, plant and human health, but perhaps the world is not so black and white that a judicious bit of tillage here and there is so impermissible. But perhaps that’s wrong. Perhaps, somewhere, or perhaps even everywhere, a long biological soil clock is starting to tick down on human agriculture.

Note

  1. In September 2016 I received an email from Laura Solano of Michael Van Valkenburgh Associates Inc, stating that Dr Ingham did not work on the George W. Bush Presidential Center project. See http://www.mvvainc.com/

21 thoughts on “Soil food webs: from farm to garden?

  1. If you raise the plant (husbanding… farming) you are a commensal and not a predator. You are still a herbivore 🙂 In many (not all) farming systems there is a seed production effort (and in a few there is even a seed breeding effort – no kidding). Merely husbanding the native flora is closer to predation, but IMHO comes a bit short of ‘ruthless exploitation’. Raising seed for subsequent crops and deliberate breeding for future crop production raises the level of investment in the welfare of the husbanded species (commensal behavior). Ruthless exploitation, to me, looks more like something a very cruel slave holder might be accused of.

    • I suppose you’re right – though, without having thought about it too deeply, the whole language of commensalism, mutualism etc seems a bit philosophically fraught to me, especially when as here the focus is on organisms as self-actualising entities. I’m not sure where the term ‘ruthless exploitation’ comes into it though – I don’t think I used it…

      • Sorry to insinuate you may have said ‘ruthless exploitation’ – I was using it as a description within the definition (which has morphed to include human behaviors such as preying on others). The more precise zoological definition is where I should have stayed.

        As for adopting more precise language to describe inter-organism relationships, I think the discipline required to make the distinction(s) is valuable. Predation is commonly associated with killing prey and as such is different than scavenging – eating the already dead. In both cases though the prey is found or caught… not cultured, reared, husbanded. Within these different lifestyle classes members of the relationships (predators vs prey for example) each evolve. As we’ve discussed earlier, we humans have evolved over the millennia since we’ve learned how to use domesticates for food. And through selective breeding the domesticates are very different now as well.

        We are still predators. Hunting and gathering still occur and are fine means of provisioning ourselves. But if you want to consider all the impacts we have on the ecology of the planet – and soils (and their food webs) as the present topic – then defining our human behavior as niche managers vs. hunter gatherer might be of service.

        • Yes, fair points. I still feel the concept of commensality doesn’t quite capture it right, but I think you’re right that ‘predator’ is wrong. Now then, any thoughts on the rest of the piece, Clem?

  2. On the rest of the piece:

    I was semi-impressed with Richard Mabey’s piece in the Guardian. I think he generalizes too much as to the level of human interest in the plant kingdom. An average Mick on the byway may not know a fig from a frog, but there still are quite a few plant lovers among us. And his take on plant sexuality seems amateurish from a botanical perspective (though I must admit the man can turn a phrase and paint a picture). Still I found myself wondering how his piece demonstrates that plants ‘know’ what they want (as though they might accidentally still exist somehow if they didn’t know what to be doing)… And as for us not knowing what our crop plants need to thrive at any given time – there is a very mature literature in the field of soil fertility; there is hydroponic plant production (about as artificial as you might get) and still we are able to prescribe an elemental cocktail that will offer exceptional plant production. I agree one may argue about the finer points of “thrive”, but successful growth from seed germination through to seed production on par with natural systems suggests we have accumulated a couple clues about the chemical requirements some of our crop plants require.

    As for the conflict between Elaine Ingham and the USDA agronomists, I think we are arguing about scale. And I think you’re right to make the point that there is a big difference between dumping tons of material in a small space vs. trying to imitate the same over a whole landscape. Where I think we need to quibble is the measure of how much organic material is left in the field in the course of modern broad acre production. Cover crops are garnering quite a bit of attention on our side of the pond. But even before we go there it should be noted there is an impressive amount of material produced in the course of a monoculture corn crop for instance. In a field producing a mere 175 bu per acre corn crop (mere… our little corn rotation where I work was over 200 bu this past summer – but the corn belt average is closer to 160 bu) – anyway, at 175 bu/A one should count on having about 4.5 ton of corn stover left in the field. See this link:
    http://msue.anr.msu.edu/news/harvest_index_a_predictor_of_corn_stover_yield

    This amount of material left on the surface becomes part and parcel of the soil. Is it a lowly 1mm increment? It surely isn’t many times the 1mm, but it is a contribution in the right direction. Can this level of production be achieved without brought in fertility? Perhaps, but it would be VERY difficult. To the point of moving material about, however, how sustainable is carrying in a few hundred pounds of fertilizer to produce in place 4.5 ton of stover (while simultaneously producing 4.5 ton of corn that can make everything from diapers, swine and chicken feed, and even the dreaded high fructose corn syrup (or the amylopectin Robert Greer is so afraid of). And so long as I have to give the corn crop some kudos I may as well suggest there are underground materials left behind (roots are not part of the stover calculation). These roots provide food to the soil web and once rotted leave channels in the soil (unless disturbed by tillage). Season long the crop also creates habitat and provides ecosystem services beyond the stover, roots, and grain that we take for ourselves.

    We might also look at long term yield performance to wonder how detrimental long term repeated fertilizer and pesticide use are for the soils we rely on. There is a wealth of data going back well over fifty years in the US corn belt showing trend increases in corn and soybean yields. Some of the increases come from breeding better corn and soybean varieties, but a good bit also derives from improving agronomic practices (pest controls, etc). If all the fertilizer and pesticide were poisoning this soil, it sure has a funny way of showing it (and you rightly predicted someone would doubtless argue this point).

    Fungal hyphae are incredible. No argument there. But not all fungi are beneficial to us (in the sense they can harm our domesticates – the niche we’re constructing). Tillage can help control harmful species and reduce or eliminate the need for fungicidal pesticides. Tillage does require a significant labor input (mechanical or biological), but pathogenic fungal and oomycete control are not its only benefits. Tillage can modify the oxygen balance in the soil in a rapid manner, allow for greater water infiltration rates, and clear the surface for more rapid warm up in the spring. But tillage can also be done poorly and leave compaction, reduce water infiltration, and expose the surface to wind erosion. So tillage is not a panacea.

    I mentioned cover crops above. These may well be just what we want as we move down the road with our agricultural systems in the future. Composting in place (on site), appropriate pest control practices, careful fertilizer use, continuous improvement of domesticates through breeding, and digging even deeper into soil biology are all ways we may keep the upward trend in crop yields going. If there is a long biological soil clock ticking down on human agriculture it seems to have a pretty odd way of showing itself.

    • Thanks for the detailed comment, Clem. I was kind of expecting you to say something along those lines, and it chimes with a slight scepticism I had about Dr Ingham’s presentation. Though to be fair to her, it was very much an overview talk to a non-specialist audience. Still, I’m not as yet wholly persuaded either way – soil loss is a big agricultural issue globally notwithstanding best practice in conventional tillage farming, and I do wonder about the nutritional side of things long-term. I think I need to self-prescribe more reading and thinking on this one…

      • On the nutritional side of things I think there is still quite a bit for us to discover. I mentioned above that fertility research can prescribe levels of nutrients (elemental) that are needed to produce a comparable amount of seed (or other plant biomass). I’m not aware (and haven’t actually looked) of work describing the relative quality of the comparable seed (or biomass). I made a nod in that direction with the “thrive” reference.

        Mycorrhiza are very beneficial in some systems. There is cost to the host plant, and because of the cost one can obtain better yields by supplying all the elemental needs directly. But the yield difference resulting from reliance on symbionts (legume rhizobia also have a cost to host) may be a tradeoff worth paying in many (most?) agricultural systems.

        Beyond the cost/benefit of working with soil symbionts there are the more subtle taste matters that come from plant production in ‘healthier’ environments. The most direct example I can think of is the difference between a glass house and field grown tomato. And having grown more than my share of tomatoes over the years I think one can even discern variation among field grown tomatoes based on the quality of the soil they’re grown in. I won’t suggest that these less aromatic and tastier tomatoes are somehow more nutritious – I’ve no idea. But given a choice I know which I prefer to eat.

        Soil loss from a global perspective is a real concern and I’m glad you point that out. The good news side I’ve presented above does focus only on one landscape. And this Midwestern US landscape does have some issues that I’ve completely passed over (offsite nutrient movement likely the most significant). Globally there are lots of factors like land tenure that prevent wide imitation of some of the things that help the US example get to where it is now.

        Another issue on the plant nutrition front that I think we’ve talked about here at SFF before is phosphorus and potash nutrition in the future. As these are typically mined for use as brought in fertilizer nutrients and mines are finite resources there will need to be some new practices/technologies for sourcing or maintaining these two macro nutrients in the world our great-great grandchildren will inherit.

        Mycorrhiza are very helpful on the phosphorus side… see how we tie this up with a bow?

      • soil loss is very much an issue on my small farm, but not in the way I thought it would be. as a small farmer, who started out subsistence “peasant” farming for our own needs and self sufficiencies (organic, permaculture-y and dabbling here and there with biodynamic practices) and who has slowly but surely slipped down the shifty slope of marketing farming for the local farmers market, I watch soil and it’s nutrients, and the water it drank during a summer of drought in our part of the world – Vancouver Island – the whole lot, leave my farm all the time each and every time I sell my food to my eaters. I cover crop, I chop and drop stalks and dying foliage, I leave roots in the ground, I compost our kitchen waste, our animal waste and our human manure. But none of that, nor all of it, can compensate for or replace the biomass that leaves my farm, and never returns, in the form of food sold to outside eaters. that is a quandary and it has troubled me hugely while newly in our foray down the road of market farming, and I am rethinking the whole market farming thing, as small scale and local as we are doing it, for all its distractions and derailings from subsistence “peasant” growing, because it is an obvious and irreconcilable leak from all the closed-loop sustainable cycles (compost/nutrient/soil building cycles; water cycle; storage&recharge cycles; etc), and as such, is inherently & & absolutely unsustainable in the truest and unadulterated/unmanipulated form of the word.

        • Thanks for commenting, Mary. I’d be interested to know in what ways you’ve noticed a loss of soil or fertility from your holding in the face of selling off site. As I said above, I feel the need to research this issue more, so I’m interested in hearing people’s experiences.

          I have fond memories of Vancouver Island – though I also have memories of not much soil and an awful lot of rain in some places, which may be significant?

          • I am so glad someone is finally talking about that, Mary. That’s why farmers of old collected humanure. I think we need to tackle that one, sooner or later. (And don’t get me started about sludge.)

            But you know, this one could be solved… vacuum humanure collection could be installed for a fraction of the cost of the ongoing wars. And Sweden already put in urine collectors. All it takes is commitment.

            I am about to do an experiment — collecting all my toilet paper that I use for a week for just pee alone, btw. I am hoping I’ll feel so mortified I will finally get around to using something sustainable. like cloths.

    • Oh and I forgot to say, soil grows. I recommend the work of Christine(a?) Jones, the maverick Aussie soil scientist. Soil can grow under favorable conditions when soil remains alive. Yeoman’s method of key line plowing produced about 10 cm of soil growth in 3 years, on a pasture. That’s why the geological time frame for soil creation is misleading.

      • Hi Vera,

        Can you point me at any peer reviewed or authoritative studies looking at soil depth increase (or soil carbon percentage increase etc) from using keyline? I’ve looked for studies of this nature but I haven’t found anything. I’ve asked enthusiastic practitioners of this approach for such data without success to date. Of particular interest is any studies undertaken by independent researchers that have examined the claims made by proponents of keyline.

        Doing keyline isn’t cheap. I would have expected that contractors charging thousands and tens of thousands on larger properties for this work would be able to provide solid evidence of the soil increase but I haven’t found this to be the case.

        FWIW IMO Yeoman had some interesting ideas. Some peer-reviewed studies to see how they work in practise would be useful

        My two bob’s worth

        David

        • Don’t have any, David. And until the mainstream gets interested, there probably won’t be any… takes commitment from researchers who are also practitioners.

          It’s one of those catch 22 situations, like in alternative medicine. Mainstream research will spend money to shoot it down, but not to validate it. (Same with medical marijuana research, though that’s changing.)

          I think the best approach currently is to talk to practitioners whom you find trustworthy and who can provide credible anecdotal data from their own experience. Joel Salatin in Virginia said, for example, that the soil on his farm in his father’s day was so thin they had to use tires filled with cement to sink the fence posts. And now, a very different situation under his management. (Can’t remember if he uses keylines. But he seems credible about massive soil growth.) And there seems to be quite a following regarding keylines in Oz, where the soils are pretty poor in lots of places.

          Mainstreamers seem to be jumping on the “soil food web” bandwagon. though. I recently saw a study in Science about that.

          • A wonderful discussion! Makes me wonder, though, how a highly trained and somewhat sympathetic soil scientist would make such major bloopers. She starts off with completely unreasonable expectations. Where did she get them? I distinctly remember the 10 or 11 cm of soil in three years. Either it was Yeoman, or one of his early followers. That is much more modest. That she sets up a strawman right off the bat is not very scientific, now, is it?

            She does not describe many other factors, as the discussion points out. Much data missing. When “nothing happened” she concludes keylines are not credible. To that, I say, “not so fast, buster!”

            Yet another problem is doing keylines in isolation. I suppose you could do it, but then you’d have to at least vary your soil and climatic conditions. (Doing it in isolation from all other factors may be a mistake, though.) You’d think the experiment design would have been more thought out. — Thanks Chris!

  3. Chris,

    My experience is that simply growing food generates a fair amount of compostable material – or stuff your pigs & chickens can eat so it isn’t that difficult to make at least some compost.

    Secondly how much is needed on soil that is in good heart? The HDRA suggests not much .

    Also how do you organise agriculture If we went for Chinese style intensive horticulture then generating the material for compost and then composting it might not be so difficult

  4. Thanks for the comments, and for the interesting link Vera. To be honest, I’m a bit suspicious of some of the claims made by and/or for Jones, Yeoman, Doherty et al not to mention Savory…and maybe Ingham. It’s good to have a few mavericks, but they’re sometimes treated with a bit too much credulity. But I agree with the low till rather than no till mentality. John, not sure about how much to add to soil in good heart. But then its ‘good heart’ probably means it’s had a lot added in the past. If you’re cropping heavily and selling off site then I think you have quite a job to retain its ‘heart’. But how much of a job? I’m not sure. Winter leaching is another issue of course. I’m all in favour of Chinese style horticulture…but it’s quite labour intensive, perhaps? I guess we need some quantification in this area.

    • Well, you need people who are inspiring enough to change people’s minds, and what’s even harder, people’s behaviors. So then there’s the temptation to overstate the case. I think taking people with a pinch of salt is good, but what they say about soil growth makes sense to me. It would be nice if people who have the wherewithal would do proper experiments so we know what works best where.

      And btw, the terra preta in Amazonia is soil that grows at a pretty decent clip… people who are blest with it often sell a bunch, then let it sit and regenerate all by itself. With a little help from its friends, tropical heat, plenty of rain, and all the plant litter. When you compare it to other (usually poor) tropical soils in the vicinity, it’s downright miraculous.

      Glad we are in sync on low-till. 🙂

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