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Physical Properties of Soil

Physical Properties of Soil

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The physical properties of soil is a key driver of plant production. Therefore, it is important to understand the physical properties of soil in order to correctly management our soils. In this article, we’ll be discussing the four most important physical soil properties, they include: soil texture, structure, porosity and bulk density. 

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Soil Texture

Soil Texture is one of the most important physical properties of soil and describes the soil particles and the proportion of these soil particles in the soil. Soil texture describes the amount of clay, silt and sand in the soil. The amount of each of these in the soil are determined by the parent material, formation, and age and determines both chemical and physical properties of the soil.

Clay is the smallest soil particle having a diameter of less than 0.002mm. Clays are very important as they have a negative charge and drive cation exchange capacity and water holding capacity. Soils higher in clay tend to be higher in fertility.

Silt is next size group of soil particles and range from 0.002 to 0.02mm in diameter. Sand is the largest soil particle ranging in size between 0.02 to 2mm in diameter. Soil components larger than 2mm in diameter are classified as gravel and are not include in fine soil. 

Soil texture cannot be easily changed (or changed at all in many cases). This is due to the nature of soil formation and delivery method.

Soil Texture can be described using the Soil Texture Triangle which describes the soil depending on the proportion of clay, silt and sand. Soil texture can be described using clay, silt, sand and loam (which is a mix of all textures).

physical-properties-of-Soil-Texture-Triangle

Soil Structure

Soil structure is the way in which the soil particles hold together. Soil structure is an important property that determines many functions of the soil, such as water infiltration, gas exchange and root expansion. Structure ranges in size and shape and include:

Single Grain

Granular

Blocky

Platy

Prismatic

Massive

 

Porosity

Porosity is the measure of how much empty space is in the soil for gas and water (called Void space). Having good porosity is very important for gas and water exchange, and root exploration. Porosity is described as a percent of void space to total space. A good porosity to aim for is 50% to allow for 25% of the total space for gas and 25% of total space for water. When the gas space moves below 10%, there isn’t enough oxygen for roots to breath, therefore areas of compaction that reduce gas space to below 10% can reduce root expansion. 

Learn more!

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