Soil fraction refers to the different size categories of mineral particles found in soil.
Based on mineral particle size, sand, silt, and clay are the three main size fractions of minerals in soil. These fractions are fundamental to understanding soil texture, which significantly impacts soil properties and its suitability for various uses, such as agriculture, construction, and environmental functions.
Each of these size fractions possesses distinct characteristics:
- Sand: The largest particles. Sandy soils tend to be well-drained and aerated.
- Silt: Medium-sized particles. Silt feels smooth, like flour, and can retain more moisture than sand.
- Clay: The smallest particles. Clay particles are sticky when wet and can hold significant amounts of water and nutrients, but can become compacted easily.
Importance of Soil Fractions
The proportion of sand, silt, and clay determines the soil's texture, influencing crucial aspects like:
- Water drainage and retention
- Air circulation (aeration)
- Nutrient availability
- Workability (how easy the soil is to till or cultivate)
A balanced mix of these fractions, known as loam, is often considered ideal for many plant growing purposes because it combines the benefits of drainage from sand, moisture retention from silt, and nutrient holding capacity from clay.
Problems with Dominant Fractions
While each fraction has important properties, if a soil consists of only one size fraction there will be problems. For example, as highlighted by the reference, Too much sand, it is too dry.
Here are some issues associated with soil dominated by a single fraction:
- Excessive Sand:
- Poor water retention leading to drought stress for plants.
- Rapid nutrient leaching due to high drainage.
- Lacks structure and does not hold shape well.
- Excessive Silt:
- Can form crusts on the surface, hindering seedling emergence.
- Prone to erosion by water.
- Can compact under pressure.
- Excessive Clay:
- Poor drainage and aeration leading to waterlogging.
- Hard and difficult to work when dry, sticky when wet.
- Can shrink and swell significantly with moisture changes, damaging structures.
Understanding and managing soil fractions is key to optimizing soil health and function for specific needs.
