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Characteristics of Soil Types

The soil type in your farm, garden or recreational area will be a major factor in the type of flora you may expect to thrive. Here we look at some of the major characteristics that define different soil types.

Organic or Mineral

Broadly speaking there are organic soils and mineral soils, Soils with more than 20% organic matter are classed as organic soils. Those below this level of organic matter are classed as mineral soils.

A caveat here is the clay content. A high clay content will reduce the soil’s adherence to the organic classification and in some cases the organic percentage may ned to reach as high as 30%

Particulate Size

There are three categories of particulate that help us to define the sub type of soil

Less than 2mm (millimetres). In this category soil will be categorised as Clay if the clay percentage is above 11%.

It will be categorised as sandy if (silt%  + (clay% X 2)) >= 30%. Other compositions that fall within or outside the parameters will be categorised as sandy.

Sandy, loamy and clayey materials can also be called Humose if they contain >8-12 percent organic matter depending on clay content, and very stony if they contain >35 percent stones. Where necessary loamy materials are subdivided into particle-size subgroups as follows:-

  • Coarse loamy: >20 percent sand and <18 percent clay.
  • Fine loamy: >20 percent sand and >18 percent clay.
  • Silty: < 20 percent sand with a further subdivision into
  • Coarse silty: <18 percent clay
  • Fine silty: >18 percent clay

Full reference here:

Impact of Calcium Carbonate

Citation – Sun_Gyu Choi (Ph.D)

Using the microbially induced calcium carbonate precipitation (MICP) process, calcium carbonate crystals are precipitated in soil and act as a cementing agent for soil particles in a way like cement to increase the shear strength and reduce the permeability.

The common MICP process uses urease-producing bacteria (UPB) to decompose urea to increase ph. With the presence of calcium ions, calcium carbonate is precipitated through the following reaction:

CO(NH2)2) + 2H2O+Ca2 > CaCO3 + 2NH4

The amount of improvement is much related to the amount of microbially induced calcium carbonate content (CCC) in soil. Therefore, CCCis an important parameter to be measured for bio-cemented soil. Several methods have been adopted by different researchers to determine CCC.