Dust To Dirt

- Kerry Boyne

To start at the very beginning on this topic we need to go back to the last ice age — the one we didn’t have.

One of the main ways soil is formed is by the gradual grinding action of glaciers on rock, turning it into mineral-rich dust, which then combines with organic matter from plants and animals to form soil. Soils vary according to the types of rocks (parent material), plants, animals, weather conditions and length of time that have gone into its making.

An ice age is great for the earth’s topsoil as the temperature differences break up the rock mantle and the ice grinds it to form a new deep layer of soil. Because Australia didn’t experience the last one, our soils tend to be very old and tired, lacking many important nutrients.

As plants grow, they take up what minerals are present in the soil and when we eat the plants we benefit from those minerals. Eight of the 17 elements essential for plant growth are what is known as micronutrients: boron, chlorine, cobalt, copper, iron, manganese, molybdenum and zinc. Eventually, soil can become quite severely depleted of these nutrients.

All plant nutrients, except nitrogen, are of geological origin; they come from rocks. Volcanic rocks from lava flows have high mineral content from deep within the earth. Normal climatic conditions don’t break-down the rocks fast enough to replenish soils for crop production, so eventually the soil is depleted and cries out to be remineralised.

While the main three nutrients (nitrogen, phosphorus and potassium) are often added, the others tend to be overlooked. This is where rock dust comes in — also known as rock powder, stone dust, stone meal and volcanic rock dust, often a byproduct of quarrying.