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