PAY DIRT Healthy, fertile soil exists where many plants work co-operatively feeding underground organisms.
In the garden
As a novice gardener discovering how the foundation of the garden works seemed an important starting point. Traditional teaching of soil was that of its chemistry – nitrogen, phosphorus, potassium, pH, moisture and its texture. What has more recently come to prominence is the critical role of soil life – its biology – the plants, worms, insects, bacteria, fungi and even viruses – and their many interdependent relationships.
Soil microbiology, like any ecosystem, is a soup of elements and energy in which complex relationships allow the easy transfer of minerals and foods to any organism that requires it.
Archaeological research tells us that excessive soil exploitation and degradation over time has caused the collapse of many civilisations, from Ancient Greece to the Burren in County Clare. Their soils vanished by excessive demand and tillage exposure resulting in the soil being washed or blown away. We hear modern commentary suggesting similar problems – ‘…that land was never flooded when I was young’ or ‘there aren’t mushrooms like there used to be’.
Poor soil is compacted; it does not allow air entry nor water to penetrate and absorb resulting in surface flooding – locally we see the result in rush species proliferation. Poor soil floods in winter and dries out rapidly in summer, greatly reducing plant growth. Much of recent world flooding involves sick soils – heavy rain runs off damaged soil that cannot absorb and release water slowly over time.
Soil scientists tell us poor soil is caused by heavy compaction; ploughing that exposes soil to harmful UV radiation and rain erosion; low plant species count and agrichemicals diminishing microbiology; and surprisingly concentrated fertilisers eliminating beneficial micro-organisms.
Concentrated fertilisers ironically kill off the soil’s natural mineral-delivery microbiology system, which is particularly important for rarer trace elements critical for plant and animal immune system function. Herbicides, such as glyphosate, are toxic to many soil organisms: plants, worms, bacteria and fungi.
What is healthy soil?
Healthy soil can be described in a non-scientific description, as dark moist goo. It is high in carbon components, giving healthy soil its black appearance. Healthy, fertile soil exists where many plants work co-operatively feeding underground organisms. Soil researchers suggests ten or more different plant species in close proximity results in an exponential growth of soil microbiology, while single-figure species count results in a microbiological shutdown.
Different species have different superpowers – vetches/peas and alder trees supply free air-derived nitrogen to the soils, while tap root plants de-compact soils and deliver deep subsoil minerals to the surface. The much-maligned docks, thistles, briars and gorse are all fine performers of this natural process.
Up to 40 percent of what a plant photosynthesises is secreted from its roots to feed soil microbiology, which in turn unlocks and transports minerals to plant roots. It would seem about 20ºC is the optimal soil temperature, and high humidity (while not being water saturated blocking air entry) is perfect. If a plant seed germinates in healthy soil its root will be infiltrated very early by beneficial soil fungus which supercharges its roots, greatly increasing its ability to obtain water and nutrients.
We all know that earthworms are good for soil but we rarely hear about the other thousands of species that are also critical to soil health. In addition to plant root secretions, decaying organic matter (leaves, wood, dry manure, carrion) are also food for soil organisms. Of particular interest are glomalin and humus, sticky glue like substances secreted by soil fungi. These substances act like a sponge, absorbing and storing water and essential minerals during both high and low rain fall periods.
Some regenerative gardeners and farmers plant cover crops between harvests to continue feeding the soil, and these are then cut down to feed the soil even further when it is time to plant the main crop. They always have a range of plants growing. Rotational cutting or animal grazing increases the diversity of plant species, increasing soil fertility.
These practitioners report that it takes four years to transition and wean off conventional chemical gardening to regenerative organic systems – time is needed for the soil ecosystems to regenerate. With fertiliser prices accelerating this is a pressing global issue.
It would seem the technique to convert poor soil to healthy soil is to let many plants grow, die and recycle – biology will do the rest. Soil sampling and analysis is recommended for struggling gardens to see if there is a rare but true element deficiency.
If you are interested in learning more, I would strongly recommend the presentations of soil scientists Christine Jones and Elain Ingham and regenerative cattle rancher Gabe Browne.
So in summary, this student of the garden has concluded that letting as many different plant species grow to maturity as much as possible, omitting microbiology-killing chemicals, leaving dead organic material where it falls produces the best soil – just as nature has been doing for about half a billion years.
Oliver Whyte’s garden, Coill an Chúir at Sandyhill in Westport, is a member of the Clew Bay Garden Trail. A chain of beautiful and unique private gardens, the trail opens to the public during summer to raise funds for charity (see www.clewbaygardentrail.ie for more). Each month, an article by a trail member will appear in these pages.