Soil Structure


Soil structure is a term used to describe the way that the solid particles of the soil, that is, sand, silt and clay are arranged and the amount of space or pores between these particles. Soil structure affects important properties of the soil such as aeration, water absorption, activities of soil organisms, seedling emergence, root growth and others that have far reaching consequences for agriculture. The structure of soil is determined by how its aggregates are arranged.

The Factors that Influence Soil Structure

There are some factors that predetermine the type of soil structure that will develop in a particular place. These factors include:

  1. Climate as it relates to amount of precipitation, amount of sunshine and wind activities.
  2. The activities of man and animals particularly the kind of land tenure systems practiced.
  3. The type of underlying rock from which the soil developed
  4. The natural geological processes which are prevalent in the area.

The Important Aspects of Soil Structure

The forming of aggregates of the solid particles of the soil is the single most important feature of soil structure. Aggregates are the units of soil arrangement and they are responsible for bulk density, permeability, porosity and aeration. Aggregates form layers which are separated by lines of weakness and each is described by its angular inclination and shapes. Soil profile is another term used to refer to soil structure and usually, there are three horizons of the soil in terms of vertical analysis. These are the A horizon which is the surface soil, the B horizon that is the subsoil, and the C horizon.

The forming of aggregates favours the formation of good soil structure. Conversely, the destruction of soil aggregates is equivalent to the destruction of soil structure thereby undermining its agricultural potential. The factors that aid aggregation are wetting, drying, freezing, thawing, and micro orgasmic activity, activities of plant roots and soil animals, and adsorbed positive ions. The tilling of the soil, impact of raindrops and compaction are mainly responsible for the destruction of soil aggregates. The activities of man particularly civilization, irrigation and deforestation are especially damaging to soils.

How to Improve Soil Structure

It is pertinent that steps be taken to not only preserve but also improve the structure of the soil if governments are to avoid ecological disaster and stave off the onset of acute food shortages. Consequently, a wide variety of practices have been used to improve the structure of soils. These include increasing organic content such as by manuring, reducing or eliminating the tilling of soils, avoiding the disturbance of the soil in times when they are very wet or dry, and use of ground cover.