Have you ever wondered if the soil in your back garden is the same as the soil across the street, or at your school, or where you work? What about soil in different parts of New Zealand?
All soils have some things in common. They are made up of mineral particles, organic matter, air, water, and living organisms. But soils are also different due to how and where they were formed.
Five Factors Influence Soil Formation:
Living things inherit characteristics from their parents – and soils do the same. The rock from which a soil is formed is called parent material. These different parent materials have different starting properties, for example, the range of nutrients. So New Zealand soils that began as pumice from volcanic eruptions will be different to those formed from sediments deposited by rivers.
Climate refers to temperature and rain. Heating and cooling can speed up the weathering or breaking down of rocks into smaller pieces. Warm temperatures and rain encourages plants and animals to grow – adding organic matter to the soil. Rain also washes rocks and soil off of slopes and dissolves minerals, adding them to the soil.
Plant roots grow down into the soil. Roots get into cracks and release chemicals that help make nutrients available. Earthworms and other animals tunnel through soil and mix it up. When plants and animals die, they add organic matter to soil. Humans also make changes to soil. Removing vegetation from the top of soil exposes it to erosion – the soil can get blown or washed away. Humans add fertilizer to make soil more productive or lime to make it less acidic.
Topography refers to the land. If a land is sloped, gravity moves soil particles downwards, deepening the soil in a valley. Topography also influences the climate. New Zealand weather patterns often come in from the west. The air cools as it rises up over the mountains and the moisture falls as rain. The air is drier by the time it reaches the land in the east, so less rain falls.
It takes a long time for soil to develop – from 500 to thousands of years for every 1-2 cm. The age of soils differs arond the country. Parts of Northland have quite old soils whereas the valleys in the Gisborne area have soils that are young – many are formed on material moved by Cyclone Bola in 1988.
Scientists have grouped (classified) soils into 15 soil orders. The soils within each order share similar characteristics and properties so we expect them to ‘behave’ in a certain manner. The soil orders are broken down into smaller and smaller categories – New Zealand has over 1900 soil series.
Scientists use the New Zealand Soil Classification System to identify specific soils. The classification system is quite detailed to allow for accurate communication between scientists.
Soils also have common names. The common name usually has the location where the soil was first described and includes the soil’s texture. For example, Timaru Silt Loam is found in the Canterbury region.
The activity Observing Soil Differences uses road cuttings to explore differences in soil. Road cuttings expose soil layers and give clues to how the soil was formed.
Visit Te Ara’s Oneone – soils to learn more about Maori and soil.
The Te Ara story Soils explains the soil orders in more detail.
Landcare Research’s NZ Soils site provides even greater detail about the soil orders.
Soil scientist Louis Schipper gives a brief introduction to soil formation in this video.