Instead of seeing soil as a ‘nutrient store’ or ‘bank balance’ of plant food, we might imagine it as a living organism which is respiring and full of life – the skin of our Earth. The next step is to consider how to enhance the lives of all those soil organisms that have the ability both to give a healthy structure to soil, and to make nutrients available to plant roots. Two simple ways of doing this are by keeping a mulch of organic matter on the surface, and by avoiding any unnecessary cultivation. Scientists have revealed much about soils’ food chain, with invisible bacteria at the bottom and frogs, mice, birds and so on at the top. At the top of this chain is mankind, which has the ability to either destroy or encourage all the inhabitants underneath.
Soil is a living, dynamic substance, and the microbial life within it is crucial to providing plant life with the food they need to grow. The microbes can be bacteria or fungi, but both need space--the pores--for a good living environment.
Soil particles that clump together are aggregates. These are the architectural building blocks of soil. Their presence has a major effect on the behavior of the soil as a community. Multiple processes form the aggregates: cycles of wetting-drying, thawing-freezing, earthworm activity, actions by fungi, and interaction with plant roots.
Courtesy of California Academy of Sciences.
Maintaining soil health
A first step is to avoid regular use of synthetic chemicals that irritate or even destroy many soil inhabitants. And be extremely careful in their use – for instance, it’s better to use just two or three slug pellets under something like a piece of wood, then retrieve and bin the poisoned slugs. A second step is to avoid cultivating soil as far as possible. Thirdly, most positively, we can increase soil life by adding organic matter to the surface, keeping the most finely decomposed compost for plots where vegetables are grown. Adopting all three of these practices together is self-reinforcing. Not digging soil, for example, will lead to a more healthy soil population and more vibrant plants. Your plants then require less chemical assistance to keep disease at bay, especially when they are well adapted to your type of soil, location and climate.
Buying compost and manure
Home-made compost can be supplemented with bought-in compost or manure. Black and crumbly green waste compost and decomposed organic compost are often available at reasonable prices from Government Agricultural centres which are produced from Landfills by the Urban Councils. Animal manure can often be had for the cost of delivery alone and contains a lot of goodness, but is often lumpy and harder to spread evenly. Horse manure is better for heavy soils and cow manure for lighter soils. Many gardens in the past grew fine plants in soil improved with horse manure.
The soil food chain
There’s an incredible dynamism and intelinkage to the working parts of our soil. Blocking of any one group of organisms has bad effects on the others. We need them all.
- Bacteria are vital to the planet’s health.
There may be half a million in a teaspoon of healthy soil, mostly helping to decompose organic matter. When bacteria die, the nutrients they recycle become available to plants. - Fungi, unlike bacteria, can travel by increasing in length, helping to aerate soil and move nutrients around. Plant roots use mycorrhizal fungi to fetch and unlock minerals, especially phosphorus.
- Protozoa include amoebae, ciliates and flagellates, which work with and, mostly, live off bacteria. Protozoa may supply as much as three quarters of plants’ nitrogen requirements.
- Nematodes, or roundworms, are prolific and mostly beneficial, consuming everything below them in the chain, and some above, such as slugs. Above all, nematodes help to mineralise nitrogen.
- Arthropods include mites, spiders, beetles, springtails (‘soil fleas’) and millipedes, whose main role is to shred organic matter such as leaves, speeding their decomposition.
- Earthworms make casts up to 50 per cent higher in organic matter than surrounding soil. Their digestive enzymes make nutrients more available to plants. They can open up compacted soils and increase soils’ water-holding capacity.
- Gastropods are slugs and snails, who play a vital role despite occasionally devastating our plants. Most gastropods live below the surface and convert organic waste to a more decomposed form. Their excretions help bind soil particles together.
