What is Soil Health and Why Growers Should Care About it
This piece is perhaps in the wrong order, since it should precede my other piece here but, in what follows I’d like to lay out the main tenets of soil health, some evidence I gathered for them and some examples of their application.
Before that I want to present what I feel are the main motivations for “going to all that effort”.
Why Bother?
First of all, in this climate change acceptance world, all forms of agriculture, and land use must wipe their face in terms of carbon. Being at least carbon neutral, if not carbon negative (or positive, whichever way you prefer it phrased).
Basically, if we want horticulture & market gardening to be taken seriously and to be scaled-up we need all of the ammunition we can get. I feel currently we have a unique opportunity in the context of the upsurge in interest in veganism. Our products are at least nominally the mainstay of a plant based diet.
While we’re certainly well clear of the criticisms around efficiency that are levelled at livestock production, it doesn’t mean that simply running less destructive forms of production is actually beneficial. In the face of the very real threat of 4 degrees of warming, locked-in, it’s simply not good enough to shrug and say well “that’s farming”. If we’re going to make the case against hydroponics and other soil-less growing systems our soils under cropping need to be at least as good as they would be under an average grass pasture, if not better.
All land, and all production must sequester carbon and it can, it’s been done, one example has raised their soil organic matter (SOM) from 2.4% to 8–11% in 6 years. 0.5–1% per year increases are regularly achieved.
Every single cropping cycle is a growth cycle and therefore should be net cumulative, in terms of carbon — through the process of root exudation. Simply put, all plants have the potential to improve soil (fertility), it’s the simply the management and composition of those plants (in space & in the rotation) that determine this fact. However, this is very hard to achieve when regularly cultivating, for example.
Basically if you’re serious about climate change, business as usual is not an option. The good news is if you rigorously apply the same health principles production can be carbon negative.
What’s in it for Us?
So, apart from saving the planet, are there any other arguments for adopting novel practices? Is it just about doing good? While our livelihoods suffer. No
No, basically, adopting the soil health principles wholeheartedly is one framework that can both address global issues and bring production benefits — showing that cropping (and farming) doesn’t have to be a zero sum game.
So, how would these benefits manifest? Everyone knows how well there crops look when the land is in good heart. And that that translates to fewer grade-outs or crop failures, less drought-stress, less watering, better infiltration and more yield. Moon on a stick? All of these are correlated with better soil health. Notice I didn’t say higher yield — if you wanted one pithy way to summaries the results of this approach it might be “an exercise in finding more places to sell salad (and baby leaves)”. I’m being deliberately flippant but the extensive use of catch cropping, for instance, has one main result, more, perishable yield. This may not be the yield “you want” or that asked for by current customers but one things for sure, the production potential for most land isn’t being realised. And growing this “extra yield” will have direct benefits to soil health. As well as potentially the bottom-line, once the marketing kicks-in.
Another benefit of better crumb structure will equate to fewer passes to raise a seed bed, where cultivation is practised. That’s less diesel and better windows for field access (a window that’s fast becoming undependable). Either way there’s wins to be had once we harness the latent potential of plants.
Grass & Fertility
Perhaps one of the few things that farmers (and growers) can agree on is that the land is “in best heart” the first year out of grass. So, is there something magic about grass, compared to other plants? Does it have unique “healing powers”?
Basically no, but to be clear, what is it we can say about the conditions under grass?
A living root, covered soil, undisturbed, diverse (ideally), some animal impact (potentially) and few if any chemicals.
Soil fertility (health) can and should be built within the cropping phase of our operations, and can be achieved without going to grass. Not that grassing-down and fallowing aren’t efficacious practices, just that we have more tools available to us that are perhaps more appropriate in a cropping situation. We just need to closely mimic those conditions we find under grass, and that’s where the soil health principles come in — 7 ways to help you select management practices, and to make decisions on your operation that build soil: cropping or fallow, spring or fall.
One key insight — microbes matter
Perhaps the most important single insight that underpins, most, if not all of us or health principles is the understanding that microbes matter. And they matter to us the growers. But, why do they matter? what’s so good about them? and, what do they do for us?
Answer 3 things.
Firstly they literally create crumb structure. Their actions bind together disparate soil particles into crumbs or “aggregates”.
Secondly, they feed plants. They digest elements out of the soil mineral matrix (as well as organic matter) and transform them into plant available nutrients. They literally eat rocks. Hitherto known as decomposition but since the process is done enzymatically it’s much more akin to digestion.
This is what’s known as the “microbial bridge”. Simply put, plants (and healthy plants in particular) are nourished by nutrients provided by organisms.
Thirdly microbes protect plants. Through a number of different mechanisms they either out compete or shield plants from disease-causing organisms and often pests as well. Perhaps the poster child of this final point is mycorrhizal fungi that snare root feeding nematodes which when caught are then digested and past up to the host plant.
So the plants are getting a pretty good deal here, no? It’s getting a nice loose structure to push its roots through easily, it’s got room service and it’s own live-in healthcare service. Is it getting all that for free? Emphatically no, this is where the soil health principles come in, read on.
The Soil Health Principles
1 The Living Root — maintain a living roots in the soil for as long as possible and as often as possible
This is number one on the list because perhaps it is the most important. Because, simply put, roots make soil and they do this by producing root exudates, — carbon secretions that feed (and recruit) soil organisms, which in return deliver plant available compounds, right in the “root zone”.
If you want to see the effect of the living root on soil structure examine the soil around the roots of the healthiest plants on your plot. What are likely to be the healthiest plants on your plot? Basically weeds (see above). So the next time you’re out in the field, weeding take a moment to carefully lift one or two plants and examine those roots. You will typically notice finally grained soil that has excellent crumb structure, potentially some of which may be actually stuck to the roots themselves, in what’s called a “rhizosheath”, this is a phenomenon seen where microbes are active and producing the glue like substances that bind together soil particles into aggregates. Where you see rhizosheaths you can infer from that that root exudation is taking place, as, without this carbon (energy) source these organisms would be inactive.
What you are seeing is soil building in action — where you are seeing crumb structure around roots and rhizosheaths. Without roots and root exudates, organisms become inactive, microbial populations become simplified and ultimately aggregates become consumed by those same organisms, since they have nothing else to eat, as these, glue-like substances, are all organic (carbon based) for example polysaccharides, hence are comestible. Literally the structure of aggregates is edible, Think Hansel and Gretel.
2 Covered Soil — protect soil, from wind, rain and sun, with leaves or residues
This is perhaps the most controversial of all of the soil health principles, for growers, since it’s normally reduced to the instruction of mulching, which as many growers will attest to, can be a magnet for slugs or at least is closely correlated with additional slug activity. And nobody likes slugs (except perhaps ducks and (when trained) chickens but that’s another matter).
However, maintaining a soil cover is essential just as the other soil health principles. This is a fact that “nature intrinsically understands”, this is why bare soil is such a magnet for weeds, because without a cover, soil degrades quite rapidly, nutrients are lost, soil caps and water runs off. Ultimately that porous structure crumb structure that we all value is sacrificed.
Does that mean we should be covering every inch of our soil with straw every moment of the growing season? Well probably not. But it does mean that we should be taking steps to reduce the frequency of bare soil as well as the length of those periods. One simple example is to use rolled out round bales to plant alliums through. Growers have reported good success with this and the mulch itself is a very cheap way to buy nutrients.
Bare soil is the enemy of soil health. Don’t farm naked as some say.
3 Minimise Disturbance and Compaction — reduce tillage severity and frequency
No dig and no till are perhaps the poster children of the soil health movement but certainly it shouldn’t be reduced to this one single measure. That’s not to say that tillage isn’t bad it is, very, but that simply shifting to no-till and making no other changes will not bring the kind of results that we are really looking for. It will not bring health back to the soil on its own, it must be coupled with the other principles and particularly diversity, see below. That said it’s worth expanding on the rationale for not tilling, by laying out the issues with tillage itself.
The first and most important point to make is that tillage destroys soil structure. This seems counter-intuitive because one of the primary reasons for tillage is to improve structure, or to get a tilth. While certainly there is a loosening effect post tillage, this is a short lived phenomenon, however, the structure of the soil is soon lost and it will then settle back into it’s more native, mineral-structured state, more akin to the subsoil. If all conditions are right then the crop can be established in this short phase, but this window is getting more unreliable by the day.
The reason that tillage destroys soil structure is because when we are talking about crumb structure we are talking about aggregates ultimately, and what are aggregates made of they are made of is small soil particles bound together with glue-like substances that have been secreted by organisms. When you till you break open these aggregates you split apart these crumbs exposing them to oxygen at which point “R-strategist” organisms invade the space and rapidly decomposed or digest (literally eat) the binding agents that glue together these crumbs. The process of aggregation is directly analogous to that of making biscuits in that the homogeneous flour (and sugar) particles are bound together by the butter or fat into larger non-uniform (heterogeneous) clumps or crumbs. In this analogy the sugar is analogous to sand and the flower is analogous to clay. And the fat is analogous to those binding agents, those polysaccharides that are biologically derived in the same way that a fat is.
Generally speaking if you want retain good crumb structure then reduce tillage — reduce the depth-, the frequency and minimise inversion.
That said, is there a place for tillage as a force for good in a horticulture operation? That depends much on the starting point. But there does seem to be a small number of clear cases where tillage (or mechanical interventions in general) can help to rectify the situations related to past management.
If your starting point is tired old pasture (but I thought you just said that pasture takes all the soil health principles, well yes it does but management is always superior).
See pic below. Old pasture (especially horse) may well be heavily consolidated and there’s only so much that your crop roots and even cover crop roots can do to undo this situation. Certainly the Real Food Garden had good results with ploughing the existing pasture and then a year of cover cropping before conversion to no dig.
Further to this I think non inversion tools like broad forking on a small scale, and subsoiling at the field scale, can help to cleave open those lower layers of mineral soil, creating new frontiers that can be pioneered by organisms and roots. In this case, it’s ideal to have actively growing plants in the soil when these mechanical treatments are carried out so these roots can rapidly occupy these new zones. If not, the likelihood is that these clods and the soil itself will just settle back into its native structure, this is especially true in heavier soils, in wetter conditions.
The final thing to say perhaps under this heading is to address the very reasonable concerns around the economics of this type of approach. One observation from a conversation that was had whilst touring the Sims Hill site on one of my courses this year was how uncontroversial no-dig is in polytunnels for instance. Perhaps the route to achieving more no-till across the site is to make the conditions of the field operations more akin the cover growing situation. And thus mimic more of those economic factors.
4 Diversity — increase diversity in your plantings and rotations
Diversity above ground feeds diversity below ground. If you want your plant to have a balanced diet it needs to associate with a diversity of organisms that mineralize a diversity of nutrients.
It’s been shown that so that the formation of humic substances and stable aggregates is closely correlated with below ground diversity.
Below ground diversity requires a diversity of foods, from a diversity of root exudates etc.
This is one realm where cover crops can really excel. We can bring in so much diversity. And so long as we’re destroying without tilling, we can retain a significant portion of that beneficial structure. This diversity can be so much more, it can include C4 plants, which are rare and general in the UK cropping situations. Plants like maize, millet, sorghum, quinoa, amaranth, and the more common sunflower and buckwheat.
All these fancy seeds in a mix sounds expensive, no? Well it doesn’t have to be, just source your seeds from the feed merchant, rather than the seed merchant. Bird seed mixes are a great starting point and have most of them already have the 8 species or more, recommended: broadleaves and grasses, warm season and cool season. Add to that starting point any old seed or “spare” seed that you’ve got lying around: veg, flowers, whatever, some tall-straw cereals like rye, or population wheat, and you’ve got yourself a banging mixture for little money. And when the costs are that low you can start sowing at proper seed rates which maybe 2 times or 3 times the standard advice. This overcomes the main pitfall people have when experimenting with cover crops: too little seed.
That said, diversity isn’t limited to cover cropping. We can introduce diversity into our cash cropping operations. This is potentially where some of the biggest wins are actually to be had. Given that increasing species diversity from 1 to 2 represents a doubling in diversity that’s a big win. And going from 2 to 3 represents another 50% increase. So, include: catch crops, intercrops and relay crops whether practical. Even planting different varieties of the same crop in the same bed. Harvest- or thin out young plants for baby leaf production. But above all, find new markets for that additional produce.
There should be gains to be had in this case, so long as we doing our due diligence with the other soil health principles — especially around bare soil and the living root. Again we don’t want massive space between the plants being unfilled with roots and uncovered. This is where intercropping and catch cropping can really pay dividends.
The image from Hilltown organics gives one example of how the diversity lever can be engaged in the cash cropping phase. It may not look pretty and certainly there’s a penalty in harvesting. But the gains around plant health are significant. The image at the head of the article shows how they’ve produced 6" of top soil in between 2012 to 2018, without going to grass.
This may well suit a pick-your-own system also.
5 Feed Soils — hungry organisms need food to stay active and healthy
This is definitely one area where the organic crew got it right. But what do we mean by this? What eats stuff in soil? Well organisms, life, life eats stuff. Not the “soil” per se, as this is simply a matrix of geological degradants.
What actually eats stuff in the soil is soil organisms: the soil food web members. So the question is then, what do these soil organisms like to eat? Really we’re talking about fungi and bacteria in this case, as they make up the vase majority of soil biomass. So, what’s their preferred food? Well in this case it’s root exudates. Simple to utilise (metabolise) foods such as carbohydrates, often as straightforward as glucose. But that is what’s being supplied by the roots, no? So, that’s covered under principal number one — the living root, right?
Well yes. Except we are in a cropping situation which means there may be a break in cropping. Where there’s a break in cropping, the organisms that are present in the soil, those active communities of bacteria for example that have built up, through your good management of cropping (and potentially diverse cropping) will all go dormant, but before they do, that they will consume the most readily available food source present. And what is that in this case? It will be the binding agents that hold the aggregates together. They will literally eat their own homes because there’s nothing else to eat. Evoking that famous phrase “burning the furniture” — when you’re snowed in and it’s freezing outside and you run out of firewood, you’re only alternative to keep warm is to burn the furniture but once you’ve done that where are you going to sit?
So what are we to conclude from this observation? Simply, where a break in cropping exists, provide a subsistence ration. This would typically be over winter. But either way, this is the prime time to apply a loose mulch of unrotted bulky organic matter potentially along with a tarp to minimise weed growth. And then if all goes well, in the spring you can lift the tarp and you will have a nice surface tilth and an active population of organisms ready to immediately associate with your crop plants during establishment.
The last two soil health principles are perhaps the least relevant to an organic growing situation. However I include them for the purposes of being thorough.
6 Incorporate Animals
Diversify your straight cropping operation by rotating animals or integrating small scale livestock into your system.
So what’s good about animals? What benefits can they bring to a cropping system? Firstly, their manure contains inoculants that are rare, even in good compost and they can carry out the work of distributing (or applying) that manure through their own natural behaviour.
That said the key rationale behind this particular principle is that all ecosystems contain animals as part of the web, and they add a whole new dimension of diversity to the system so perhaps they should come under principal number 4, but in this case the desire is to be explicit.
In the case of organic horticulture operations chickens and ducks seem like the most straightforward option, with chickens being useful for terminating cover crops in tractored system. The tractor itself can be used to flatten mature cover crops and the chickens can then glean any ripe seed and help to scratch over the haulms of the remaining plants. They can also be trained to eat slugs. Obviously as well as this, ducks can also be incorporated.
Though neither option is necessarily highly indicated in many horticulture situations, there are working examples of them working well, keeping slug- and pest populations under control.
7 Minimise Use of Chemicals
Simply put, the use of chemicals and synthetics undoes all of your good work further up the list.
Firstly, use of synthetic fertiliser or soluble nutrients in general discourage, the production of root exudates. Basically root exudation is a quid-pro-quo for plants. They’re effectively paying for nutrients in a form that they can absorb with energy (or sugars) the only currency plants hold. So, when a plant is artificially nourished through soluble fertiliser applications it’s need to offer exudates is removed, though this is fine in the short term, however, the removal of foods from our friendly minions (the soil microbes) means they will at best go dormant and at worst start chowing down on the aggregates themselves because there’s nothing else to eat and then go dormant.
Fertilisers in salt form, and in very high concentrations, actually force their way into the plant structure. So the plant almost becomes over nourished or certainly has no control over the quantities and types of nutrients that enter the cell structure.
Further to this and perhaps, more obviously is the use of pesticides etc which basically have all sorts of impacts on non-target species. But it goes without saying that applications of fungicides for example have detrimental effects on mycorrhizal fungi, though that said, so does tillage.
Putting it all together
Ultimately the strengths in this approach, this framework, is that the principles can be applied individually or in consort. But ultimately the real wins are to be had where all of the soil health principles are applied both in the cropping phase and the fallow periods.
Where this is the case we can see quite radical improvements in soil structure and soil health.
The picture below shows the soil from Hilltown organics where they have turned consolidated heavy upland soil formerly under pasture into loose friable and well aggregated soil by applying all of the soil health principles.
I like to think of the soil health principles as different levers maybe like you might picture in an old signal box, or a graphic equaliser. With each lever representing a different principle. Ultimately, over time want to be able to push all of the levers up to full, bring all of the benefits to bare.
Furthermore, for each principle there’s obviously a range. Similar to gears on a gearbox. Ultimately where limited by equipment or tools, it’s like being unable to change up from 3rd gear for instance. There’s nothing worse than being stuck in 3rd gear on the motorway. If we can gradually increase the upper maximum we can achieve each year we will gradually be able to leverage more of the latent power of nature to grow better crops.
Conclusion
So in conclusion, the soil health principles are basically another iteration of nature mimicry, offered, in this case to farmers and growers as a tool for decision-making on-farm.
Simply put, where two options are considered for a particular situation, that which scores highest, in terms of the soil health principles, should be preferred, where practical, or when it becomes practical.
I hope that you will use these principles in your day-to-day practice and in your longer-term rotation planning.
And for those that want to find out more, or discuss this in more detail please get in touch or consider joining me on one of my soils courses this autumn.
Courses & Info
https://www.facebook.com/pg/nielscorfieldland/events/
Further Reading
Part 2 — Realising the Promise of Soil Health in Organic Horticulture
https://medium.com/@nielscorfield_90202/no-till-for-growers-realising-the-promise-of-soil-health-in-organic-horticulture-646fd553257
