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What is Good Fertile Soil? - Soil Structure/Texture

Updated on June 29, 2013

Secrets of a Good Soil Fertility Part 1

Most of us want to achieve 'Good Garden Soil' ideal for growing plants, but have little idea of what we are dealing with in the first place. For a lot of people, simply digging a hole and planting a plant, may be add some compost with a little a fertiliser to boot, is all that is required. This approach is often done out of ignorance due to the lack of knowledge of the type of soil they have, the type of plants they've bought and what they they want to achieve. In the following articles we will gradually buildup the necessary understanding to achieve healthy soils and healthy plants.

So, what is soil?

Good garden soil is made up of a number of different mineral particles derived from rocks, and organic matter derived from plant and animal material.

Soil particles are formed as a result of three different forces, physical, chemical and biological. Firstly, the physical forces such as weathering, by the actions of wind, rain, snow, sun and cold. Water freezes in cold weather and the water molecules expand causing the mineral particles to break apart. Paradoxically, the hot sun will also cause the same effect on the surface of rocks too. The abrasion of wind and rain, picking-up fine grains of sand, rubbing against the surface of rocks will also result in the formation of soil particles.

Secondly, chemical weathering will dissolve soil mineral particles by the exposure to pollution, oxygen and carbon dioxide; all of which will dissolve in water to form weak acids and it is these that gradually erode the rock surface to form soil particles.

Thirdly, biological activity by mosses and lichens for example, can cause soil particle formation by producing weak acids to dissolve rock particles.

Good garden soil has 45% mineral content and 5% organic matter, with rest made-up of air and water. Soil without organic matter and the various types of bacteria, fungi and other micro-organisms is unable to support plant life, as shown in desserts.

Soil Layers

Soil roughly comes in 3 layers, topsoil, sub-soil and bed rock. The topsoil contains the highest levels of organic matter and therefore the highest concentrations of micro-organisms, whom convert the organic matter and mineral particles into plant available nutrients. Subsoils comprise mainly of mineral particles formed from the bed rock below.

Soil Texture

Soil texture is determined by the ratios of 3 different sized soil particles, sand, silt and clay; sand being the largest particle size and clay being the smallest, and it is the ratios between these 3 particle sizes that will determine the soils ability to hold onto water and nutrients.

Soils with a high sand content have a poor ability to hold onto moisture and nutrients, and this is due to the spaces between the particles being too wide. Silty soils have a better water holding capacity and has the feel of flour when rubbed between fingers. And finally, clay soils can hold onto a lot of moisture and nutrients, due to very small spaces between each clay particle and can be formed into a sausage when rolled.

The Best Garden Soil!!

The best garden soil contains, 30-50% sand, 30-50% silt, and 20-30% clay, with 5-10% organic matter. A simple test to determine the levels of each these particle sizes is to take a large jar, fill the bottom third with soil and add water (leave a space at the top), replace the lid, shake up and down for a minute or so until the soil particles have separated and leave to settle.

The particles will separate into 4 distinct layers within a few hours, sand at the bottom, followed by silt, then clay, and hopefully some organic matter on top. After 24 hours, measure the thickness of each layer with a ruler. To determine the percentages of each layer, divide the depth or thickness of each layer by the total depth of all three layers and then multiply the answer by 100.

Having found out the percentages of each particle size, this will then tell you whether you have a clayey, silty, sandy soil and if you have equal proportions of all three, then you have the ideal, a loamy soil.

Soil Structure

Good soil structure is the sign of good growing conditions, with ample drainage between soil particles whilst having good capillary action. It can withstand torrential rain, droughts and compaction. Some poor soils will crumble easily in your hands like sand, when you crush it between your fingers, or get airborne in strong winds. Strong clay soils will be hard to break apart when dried.

Also, soils with good structure will have good air circulation with good biological activity. Roots will be able to penetrate throughout the soil and there will be a higher level of micro-organisms and larger organisms such as earthworms.

by Alistair Olver

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    • Bob Ewing profile image

      Bob Ewing 4 years ago from New Brunswick

      wise gardeners grow soil and let the soil grow the garden, good article.

    • vocalcoach profile image

      Audrey Hunt 4 years ago from Nashville Tn.

      I love planting vegetables and learn something new every year. This complete information you have so kindley shared is necessary to know and until now I didn't know that much. I'm so glad you wrote this.

    • Alistair Olver profile image
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      Alistair Olver 4 years ago from Wiltshire, UK.

      Thanks for the support, glad you liked the article.

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