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Gardening and the Properties of Soil

In order to grow healthy plants and flowers, healthy soil is a must. Soil is a mixture of organic matter, minerals, liquids, gases, and many different organisms. Soil is said to have four main functions including it being a medium for the growth of plants, a means of storing, purifying, and supplying water, a habitat for countless organisms, and a modifier for the atmosphere of the Earth. All of these factors actually modify soil. The physical properties of soil are texture, structure, density, porosity, consistency, temperature, color and resistivity; all of which can vary depending on where the soil is located.

Soil Texture

The mineral component of soil include clay, silt, and sand. The relative proportions of each materials will determine the texture of soil. Other properties are influenced by the texture of the soil, including permeability, porosity, water holding capacity, infiltration, susceptibility to erosion, and the shrink-swell rate. The texture of soil also affect its behavior, particularly, the capacity to retain water and nutrients.

Soil Structure

When the soil textural components of clay, silt, and sand clump, it causes aggregates to form into larger unis and creates soil structures known as peds. The peds then evolve into different units that vary in size, shape, and degree of development. The structure of soil can affect water movement, aeration, plant root growth, conduction of heat, and resistance to erosion. Soil structure can provide information on organic matter content, texture, past soil evolution, biological activity, and more. Soil structure is classed based on the size, shape, and degree of development of peds.

Soil Density

Soil density generally remains constant for any given soil. Soils that have a higher organic matter content usually have a lower soil particle density while soils with higher iron-oxide content have a higher particle density. The bulk density can vary greatly for any given soil. Soil bulk density is always lower than the soil particle density.

Soil Porosity

The porosity or pore space refers to the part of the soil that is not occupied by organic matter or minerals and instead is open space occupied by water or gases. In soil that is considered medium textured, and productive, the total pore space is generally about 50% of the soil volume. Pore size can vary greatly and soil texture helps determine the total volumes of the tiniest pores. The pore size distribution of soil can affect plants and other organisms ability to access oxygen and water.

Soil Consistency

Soil consistency refers to a soil's ability to stick to itself and other objects, as well as its ability to resist rupture and deformation. The consistency of soil is measured at three different moisture conditions including, moist, dry, and wet. Soil consistency can be helpful in determining the ability of soil to support structures such as roads and buildings.

Soil Temperature

Soil temperature is determined by the ratio of energy absorbed to that which is lost. The temperature of soil regulates the availability of nutrients, plant growth, seed germination, and root growth. Soil temperature doesn't change often but does have daily, monthly, and seasonal variations. There are several factors that affect the temperature of soil including water content, soil cover, relief, and color.

Soil Color

Soil colors can vary greatly with soil often featuring contrasting patterns that are easily noticeable. Generally, the color of soil is determined by drainage conditions, organic matter content, and the degree of oxidation. Various iron minerals and their content levels can greatly affect the colors of soil.


Soil resistivity is the measure of how much a soil is able to resist the flow of electricity. Resistivity is a big factor in the design of systems that rely on current passing through the surface of the Earth. The resistivity of soil can be affected by chemical content, temperature, and moisture.

Many of the physical properties of soil are affected by one another, and can overall affect how likely a soil is to be able to sustain plant life. When gardening, having healthy soil is essential for good plant growth. To continue reading about the physical properties of soil, visit the following pages.

Soil Physical Properties Overview

Tree Fruit Soil & Nutrition - Physical Properties of Soil

The Importance of Soil Physical Properties

Soil Texture and Soil Structure

Organic Lifestyles - Soil Physical Properties

Start Farming - Soil Quality

Soils and Fertilizers for Master Gardeners - Soil Physical Properties

Soil Formation and Classification

How do the Properties of Soils Affect Plant Growth?

USGS Education - What's in My Soil?

Science Topics - Physical Properties of Soil

GLOBE Teacher's Guide - Pedosphere (Soil)

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