Friday, 27 May 2016

Understanding Soil Ecosystems

I've been doing a little research into soil ecosystems. After all, this is what my no-dig approach is all about - supporting those networks of life within the soil that help to keep it healthy and full of nutrients for my plants. And what I've found out has made me even more adamant that the no dig approach is the way forward. I've also learnt some very useful new tips about managing the soil in an appropriate manner for the type of plants I'm trying to grow.

My main source has been Jeff Lowenfels and Wayne Lewis's book 'Teaming With Microbes' and I would definitely recommend this book for anyone interested in finding out more about some of the science behind the no dig approach. The basic conclusions of their book are that it's important to look after the complex ecosystems in the soil as microorganisms in the soil readily provide all the nutrients our plants need to grow just as a by product of being alive. Different types of soil ecosystems exist for different types of plants and we can manage the soil carefully to encourage the system needed for whatever we're trying to grow.

Just think about it - no additions of man made fertiliser, synthetic or organically produced, are needed in an old growth forest. Thriving and abundantly healthy natural systems exist because of this soil based support system, which can only be found in undisturbed soil. Hence the no dig approach. As soon as you dig the soil, you smash up delicate networks of mycorrhizae, you throw deep soil micro organisms to the top and bury those that prefer to be at the surface. Whole hosts of organisms can't recover from this shock and are wiped out. Their complex interconnected networks have to be completely rebuilt. Additions of fertilisers, pesticides and fungicides are also lethal to this system. Intensively farmed soils are consequently all but dead.

But when they are left undisturbed, it's an amazing system and it's something that we can support through careful management practices.

The soil contains ecosystems every bit as complex as those in the rainforest, temperate woodland or coral reef, for example. All manner of beasts make homes alongside each other - predators and prey both visible to the naked eye and so tiny we can't perceive them without magnification. In a single handful of soil, there are more organisms than there are people on the planet. Think of the worlds of activity going on in a simple back yard with all that mini life hidden beneath the surface.

They're busy at it - living, thriving, hunting, scavenging, dying, eating, excreting, creating the basis of all live above their world - food for our plants.

The main organisms we're interested in are the smallest - the fungi and the bacteria. They consume the wastes of larger soil organisms and the wastes they produce are nitrogen based and form the bulk of soil-based plant foods. Fungi produce ammonium and bacteria produce nitrates. Both of these natural forms of nitrogen are in a plant-ready format and are more easily absorbed by plants than synthetic forms of nitrogen. Neither is washed out by rain water in the same way that synthetic fertilisers are, making more food available to plants.

And handily, the soils that fungi thrive the most in are those that support the types of plant that like ammonium based nitrogen - forest soils. Bacterially dominated soils - producing nitrates - support plants that are less woody and with typically shorter life spans- your vegetable garden or lawn, for example.

Here are a few top tips for encouraging the right kind of soil food web for your plants :

- for a bacterially dominated soil (eg the vegetable garden), use a home made compost with green plants as the main ingredient. Either incorporate this into the top layer of soil or use it as a mulch on top.

- for a fungally dominated soil (eg forest garden or shrub and perennial plant based flower bed), use a home made compost with brown materials as the main ingredient. A leaf mould is ideal. Apply as a mulch. Don't work into the soil. You can also simply add woody materials as a mulch- little piles or a mulch of prunings of twigs and small branches or even woodchips can all help tip the soil food web more towards a natural woodland type.


  1. Nice interesting post. Taking the last paragraph, I do take issue with the no dig idea as it needs to be put into context. I'm trying to make a woody, shrubby area but the no dig idea physically can't work unless the soil is already sandy or loamy and free draining. Putting mulch on the surface of this type of soil may well work as worms, mice, rabbits, beetles and what ever else could possibly take some of this material down into the soil. But if you have a clay soil all you create is a plough pan. A level where water can collect and sit. Effectively you create a raised bed with an impenetrable bottom, where only a few tree roots and weeds will go down into, you haven't actually changed the main growing medium for trees, as it will still be clay.

    I've spent 4 years now doing this, applying hay, leaves, lots of twigs, manure with 50% wood chip and alsorts of other stuff piled on top.

    When I dig into the ground I find that nothing has penetrated the clay. The dog wood roots, and hazel tree roots have grown nicely, but horizontally, through this nice new soil. The problem is that the roots aren't very deep and the roots sit on top of this plough pan which is often soaking wet where the water hasn't drained.

    All your information above is correct, the top few inches are full of fungi, worms, and in fact loads of organisms, but the shallowness of this sitting on top of clay is causing a problem. Some trees have died for having rotten wet roots and a couple of others have tried to fall over because as they get bigger they aren't putting roots down into the clay.

    I think the method above may well work well in the context of good loamy, free draining soil to start with but in my situation it causes a problem that can only be dealt with by digging and working in all this organic material to a decent depth.

    No dig, even on clay, may work but with the context of many many years raising the ground level by feet with this new material laid on top.

    I'd like to be wrong because I'm at my wits end trying to create the sort of soil you talk about. I'm digging and digging and else where it is working but the amount of effort is killing me.

    I'd love to see an example of where someone else has taken a heavy soil like mine and turned it into the above without digging and within a sensible time frame, any example, that could give me hope :)

    I see that in your post you used machinery. Did you prepare the compacted soil you previously had before trying the no dig approach and laying down this organic material? If so I can see how your no dig approach can work from this point on.

    1. Hi Andy. Thanks for your comment and really useful anecdotes about your own experience with this. Yeah, I'm dealing with the same potential soil pan issues as you, gardening on top of a really heavy clay layer. I am four different techniques to try and break through and mix up that clay layer. I can't say for sure yet if what I've done is working in the long term, or which technique works best, as I'm only about three years in. There's a whole post or two in my answer to your questions!

      But in brief - I'm trying three areas with different types of tap rooting plants - my hazel coppice had a one off annual tap rooting green manure plant (fodder radish). All hazels are so far thriving, but still small - it's early days.

      My forest garden was planted with deep rooting, perennail ground cover plants (cocksfoot grass, red clover and chicory) for a year before planting began and I'm staggering planting of trees and shrubs to allow for more tap rooting action on that soil pan. Two of the first trees died. Three trees and about 20+ shrubs are still alive.

      In my 'meadow' I've pretty much just left the ground to do as it will, with a little overseeding with wild plants. Again, I'm focusing on tap rooting plants - so teasel, fennel. There are docks and thistles, which I don't worry about too much as they're improving the soil. And a few other wildflowers are thriving - red campion, oxeye daisy, chamomile.

      In a final patch, I covered the area with imported top soil and then am applying a rolling compost heap on top - a strip heap that gets turned onto the adjacent strip, leaving compost behind. I'm not very far along that process yet, so not much to report on the success of this approach. I'm aiming for a more gradual fade out between the layers rather than straight clay to straight humus. See how it goes.

      Anyhow, hope that's helpful! I'm basically trying to mimic what nature tends to do on clay soil - grow those horrible to remove weeds with deep roots! I'll write updates at some point about how it's all going.

      Thanks again




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