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.

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