What is soil?
The New Zealand Soil Classification (the system used to identify and name soils) defines soil as any natural material on the land’s surface that has the potential to support life, even if that is only bacteria. Soil scientists point out the difference between soil and dirt. Soil is a natural material in its proper place, but dirt is soil in the wrong place, such as on one’s shoes or car.
An ordered system
The soil is a natural body. It is not just a jumble of rotten rock, water, air and decayed plants – it shows characteristics of order. It shows order at the microscopic level of clay minerals and organic humus, and at the larger level in soil layers seen in a road cutting, or in patterns of soil types across the landscape. Soils link natural systems above ground – plants, animals, landforms, surface water and the atmosphere – with natural systems below ground, such as rocks and groundwater.
What soil does
All life on earth depends on soil. Soil performs vital functions in our ecosystems. The soil stores reserves of water for plants, controls water seepage into streams and groundwater, and reduces rapid runoff that could cause erosion and floods. The soil stores carbon (in New Zealand, it stores about four times more than plants), so it helps minimise the release of carbon dioxide into the air. Soil microbes help absorb nitrogen from the air and feed it to plants. Nutrients are released as the rock fragments decay. Soil filters water, and helps absorb and break down toxins.