What is Soil?

Soil is the thin layer of material that covers the earth’s surface. The qualities of soil have a major effect on the growth of plants. Plants need soil for support. Soil is also the source of mineral nutrients, and spaces in the soil hold air and water for the plants’ root systems.

Soil is originally derived from a parent material (usually rock). The rock is broken down over time by the action of water and the stresses of varying temperatures. The nutrient level of a soil is first governed by the nature of its rock of origin. Organic matter from leaves and other forms of living matter combine with particles of soil to add nutrients and affect its structure and performance.

Soil texture refers to the size of the soil particles and is usually governed by the type of rock the soil is derived from. For example, sandstone will produce sandy soils with large particles. Sandy soils drain very readily and have difficulty in holding onto nutrients.

Clay soils have much smaller particles. They are rich in nutrients but are difficult to dig and are often poorly drained.

Soil structure refers to the way in which the soil particles have been arranged together. Particles of soil bind together to form crumbs, allowing air and water to be stored between them. If a soil has poor structure it doesn’t have spaces for air and water, which makes it difficult for the roots to function.

Soils can be improved by the addition of organic matter, which forms humus. Humus is sticky so it attracts and holds nutrients. Organic matter also improves soil structure. Good gardeners continually add organic matter to their soils. It can be dug into the soil but, with established garden beds, this is usually done by applying organic mulches to the soil surface. In time the organic mulch breaks down to improve the soil.


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