It's easy to think of soil as inert matter, but in fact it's a complex and active ecosystem, with innumerable processes taking place all the time. Soil is earth's most vital organ, supporting all life on the planet.
Just a single teaspoon (one gram) of garden soil can hold up
to one billion bacteria of thousands of types, several thousand protozoa, and
scores of nematodes, not to mention the odd millipede, spider or earthworm.
Mycologist Paul Stamets says:
If you were a tiny organism in a forest's soil, you would be enmeshed
in a carnival of activity, with mycelium constantly moving through subterranean
landscapes like cellular waves, through dancing bacteria and swimming protozoa
with nematodes racing like whales through a microcosmic sea of life.
Bacteria convert
the waste products of decomposition into nitrates which plants use for growth.
Some bacteria fix nitrogen into the soil, and some assist in the creation of
humus. (Humus is the 'holy grail' of soil; the perfect end product achieved
when organic matter decomposes thoroughly and bonds with carbon and clay
minerals to reach a stable state; a non-cellular, amorphous sponge for soil
nutrients and water.)
Fungi weave their
tiny, root-like mycelium through every millimetre of soil – one cubic inch of
topsoil contains enough fungal cells to stretch more than 8 miles if placed end
to end. Saprophytic fungi – the decomposers – are vital for the decay and processing
of organic matter in the soil, while mycorrhizal fungi connect to the root
systems of plants, feeding off their exudates and providing them with more
water and nutrition from the soil, as well as boosting their defence systems
and allowing plants to send signals to each other! Connection with mycorrhizal
fungi effectively increases a plant's root system by up to 700 times! Fungi
also filter toxins out of soil water, and exude acids, antibiotics and enzymes benefiting
plant health and the condition of the soil.
Protozoa,
microscopic single-celled organisms, feed on bacteria, consuming up to 1000 per
hour, and provide a food source for larger organisms. As they consume bacteria,
nitrates are released and made available for plants.
Nematodes are
tiny, slender worms, ranging from microscopic to around 5cm long but only ever
a few microns thick. It is estimated that there are up to a million species of
nematodes, inhabiting virtually every ecosystem on the planet. 90% of soil
nematodes live in the top 15cm of soil, preying on smaller organisms and
feeding larger ones, and while a few are garden pests, others prey on garden
pests and can help to control, for example, snail and slug numbers and
cutworms.
Arthropods in the soil range in
size from microscopic to several inches in length, and include insects such as
springtails, beetles, and ants; crustaceans such as woodlice; arachnids such as
spiders and mites; and myriapods, such as centipedes and millipedes. In farm or
garden soils, several dozen species might be found in a square mile. In forest
soil, several thousand species might
be found! Arthropods can be grouped as shredders, predators, herbivores, and
fungal-feeders, based on their functions in soil. As they feed, they aerate and
mix the soil, regulate the populations of other soil organisms, shred organic
material, mineralize nutrients to make them available to plants, burrow to
improve soil structure, and stimulate microbial activity. Ground beetles are
major predators of soil pests such as slugs and cutworms. |
| Pseudoscorpion, a tiny arthropod in garden soil! |
Soil isn't static – it's constantly moving and changing,
with all sorts of nutrient and life cycles going on that we only really know a
little about. Healthy soil is jam-packed with living organisms, even if you
can't see them, and these organisms make soil nutrients available to plants. Healthy
soil is structured around fungal networks and the burrows of worms and
arthropods.
But when we dig our soil, we destroy all that's going on,
harming small creatures and exposing them to predators, killing microbes by
exposure to light and air, disturbing ground beetles' pathways, mixing up the
natural structure of the soil and forcing many of its cycles to begin again at
square one. Digging makes soil more susceptible to erosion by wind and water,
more susceptible to leaching of nutrients, and less effective as a carbon sink. In short, soil is best left alone to get
on with it as much as possible!
That's why, at FoodSmiles, I'd like to encourage a no-dig
approach as far as possible. Charles Dowding, popular garden author and no-dig
advocate, has run a number of trials comparing the results of dig and no-dig
growing, and reports healthier, stronger growth all round, slightly higher
yields for some veg, and fewer weeds – mulching with organic matter keeps them
down and digging often brings old weed seeds to the surface!
It is, however, important to make sure soil isn't too
compacted either – compacted soil allows less water and air to penetrate, is
hard work for plant roots, and suuports less life – and our heavy soil is prone
to compaction. That's why I hope the broadfork will become a key tool for
preparing soil before planting.
The broadfork
allows us to break up the soil without turning it over or mixing the layers
together. Air and water can get in again where soil is compacted at the
surface, but we don't cause so much harm to the soil's microbiology. It's a
good idea to also rake the surface after broadforking, to give a better tilth
for sowing new plants and to discourage hard crusting on the surface.
It is heavy to carry but easy to use, and though it works
your whole body, it doesn't involve any of the bending and lifting that digging
does and thus is much easier on your back! Simply press the tines into the
soil, using your foot on the crossbar – or both feet in hard areas – to push it
as deep as possible, wiggling if necessary to work round stones. Next, pull
back on the handles, bringing them down to waist level or so, to lever the
tines up and gently lift the soil. Then pull the fork out, move back six inches
or so, and repeat. One person can broadfork one of our beds in less than an
hour this way (extra helpers can assist by picking out weeds and stones, and
raking the surface over). You can see a little demonstration of how to use it in the short video below:
We will still dig if the need arises, whether from time
pressure or cultivating a new area of tough ground or to get those potatoes up,
but I hope that we can do the best for our soil by protecting its structure and
microlife whenever we can.
Additional measures we can take to nurture our soil are:
- Minimise walking on crop-growing areas, to minimise compaction, especially when soil is wet.
- Cover bare soil with a green manure (cover crop), a mulch of organic matter, or weedproof fabric to prevent erosion and protect microlife. (We weren't very good at this over winter but let's try harder.)
- When adding manure or compost, apply it to the surface and leave it – worms and other creatures will incorporate it into the soil in their own time.
- Don't work soil when it is wet and clings to your boots – it is damaging to soil structure.
- Avoid chemical fertilisers and pesticides, which upset the soil's balance and kill beneficial organisms as well as detrimental ones. (Or course, on our organic plot at Hammonds End we are prohibited from using most of these things anyway!)
References and Further
Reading:
The
Permaculture of Soil, part 3: Soil Care by Caroline Aitken
The
Soil Biology Primer, published by the Soil and Water Conservation Society
What
on Earth? Your soil health explained, produced by the James Hutton
Institute
CharlesDowding.co.uk,
website of popular author and no-dig advocate
Mycelium Running, book by Paul Stamets