Gardening and DIY: Brown gold

Photo / Sophie Barclay

Element writer Sophie Barclay is attending and reporting from the Auckland Permaculture Workshop classes throughout the year.

On a field trip to lecturer and organic food specialist Brendan Hoare's four hectare eco-farm, I fell in love... with soil.

That unassuming brown stuff in your garden is, literally, the source of everything on this planet. Healthy soil contains a varying mix of rock and minerals (including a mix of stones, sand, clay and silts) depending on where you live. It should be covered by a layer of rich organic matter - the decaying remains of life that once was - or its excretions.

The good news is, if, like me, your horticultural skills are outweighed by your ability to misidentify weeds as native plants, there may be billions of volunteers already assisting you on the quest for healthy soils.

The humble earthworm is busy tunnelling through the soil, turning leaf litter and semi-decomposed compost into nutrient rich plant food. Working harder than a DoC staff member approaching yet another review, worms create space for plant roots to penetrate soil and oxygen to infuse through to roots and other soil-dwellers. The earthworms in one hectare of land will churn through nearly 40 tonnes of earth - equivalent to a depth of around 0.5 cm of soil - and enrich it with a healthy dose of worm poop. All for free.

Another key ally is the motley crew of microscopic microbes. One single teaspoon of good soil will produce more of these fungi, bacteria, protozoa and other unpronounceable undetectables than there are humans on earth. These soil magicians turn organic matter into humus - a black, jelly-like material which the organic matter eventually breaks down into. Microbes also give plants access to soil minerals, draw nitrogen, carbon and sulphur from the air and, helpfully, make it available for our crops.

But we're losing a colossal 300 million tonnes of soil a year; nearly 10 times the global average. Our naked pastures, which were stripped of useful soil holding, stabilising trees, are especially prone to major erosion. Soils can lose their fertility, and their functionality.

Dousing the soil in fertilisers is not helping. Many studies highlight the detrimental effect that inorganic nitrogen (a key fertiliser ingredient) has on microbes.

Soil health depends on a myriad of factors:
Depth - deeper soil means more nutrients and water
Well-structured soil - ruined by human, animal and machinery compaction
Aeration
Permeability - water needs to get in and out
Water-holding capacity
Nutrient content - plants need nitrogen, phosphorous, potassium and 15 other elements ?Acidity and alkalinity
Soil stability

Next course: Built environment, learning about 'ecologically responsive buildings.' See apw.org.nz