It’s Alive!

According to July’s IYS monthly leader Mary Stromberger, “soil is a living, dynamic natural resource. It helps us sustain life — but it doesn’t do its job alone. The biodiversity of life in soil is critical to a healthy world.” 

What is soil ?

This definition is from the Soil Science Society of America.

  • The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.
  • The unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.

Life makes soil

Soil is alive. There are more species of organisms in the soil than there are aboveground. Soil-dwellers such as bacteria and fungi recycle once-living organisms into nutrients and soil organic matter (humus)—vital components of all soils. A single handful of soil contains millions of individual living organisms. Many of the ecosystem services provided by soil are actually performed by soil organisms.

Breathe of soil

From burrowers to bacteria, the organisms that live in soils respire. Most of them take in oxygen to do their work, and they give off carbon dioxide. Soil respiration is a measure of the carbon dioxide released from soil. It is released as a result of decomposition of soil organic matter (SOM) and plant litter by soil microbes and through plant roots and soil fauna. 

Soil is more than dirt



If you were to divide a soil sample into 20 parts, 9 parts would be made up of the stuff we think of as dirt: clay, silt and sand. These are inorganic particles, which means they come from non-living sources. A full half, or 10 parts, would be equally divided between air and water. The last part would be organic, made from dead and decaying organisms. The soil also would contain countless numbers of minuscule microbes, mostly fungi and bacteria, bugs, feces, nematodes, worms, roots, rotting plants, ice, minerals…

Ingredients of soil

Soil is composed of five ingredients— minerals, soil organic matter, living organisms, gas, and water. They occur in many combinations. The relative proportions of these ingredients affect how a soil behaves, what kinds of plants grow in it, and how well they grow. The mineralogy of soils is diverse. The most common mineral in soils is quartz; it makes beautiful crystals but it is not very reactive. Soil organic matter is a critical ingredient; the percentage of soil organic matter in a soil is among the best indicators of agricultural soil quality. Soil colors range from the common browns, yellows, reds, grays, whites, and blacks to rare soil colors such as greens and blues.

Recipe of the soil formation

Soils begin to form when sediment, organic matter, or rock—parent material—is first deposited or exposed, often by water, wind, or ice. Soils develop as parent material ages in place, changed by climate, soil organisms, and the terrain. Soils take shape in surprising ways—as water moves minerals and elements from one layer to another, as living organisms take out nutrients and add organic matter, or as new minerals form. Soils are constantly changing.

Soil Profile

Layers or horizon form a soil profile. Soil profiles cover the earth as 2 main layers—topsoil and subsoil. Soil horizons are the layers in the soil as you move down the soil profile. A soil profile may have soil horizons that are easy or difficult to distinguish. Most soils exhibit 3 main horizons:

  • A horizon: humus-rich topsoil where nutrient, organic matter and biological activity are highest (i.e. most plant roots, earthworms, insects and micro-organisms are active). The A horizon is usually darker than other horizons because of the organic materials. 
  • B horizon: clay-rich subsoil. This horizon is often less fertile than the topsoil but holds more moisture. It generally has a lighter colour and less biological activity than the A horizon. Texture may be heavier than the A horizon too.
  • C horizon: underlying weathered rock (from which the A and B horizons form). 


                                            Soil profile showing the different layers or horizons.

Some soils also have an O horizon mainly consisting of plant litter which has accumulated on the soil surface. The properties of horizons are used to distinguish between soils and determine land-use potential.     

Creation of soil

Soils are constantly created and lost. It can be difficult to say exactly when some soils were born, but we can say that while some are young, many are very old. The oldest soils on earth may be in Australia, where stable land forms have allowed some soils to age several million years. New soils are born with every landslide, volcanic eruption, or glacial retreat. Soils change over time through a host of biological, chemical, and physical processes. Living soils sustain life on Earth. They are born, they age, they breathe.

‘Soil’- Biological bliss

A teaspoon of rich soil can contain one billion bacteria. There are a host of small, medium, and large organisms that live in soils, including mammals, birds, insects, and protozoa. Soil microbiologists are applying advanced molecular techniques to understand the diversity and function of soil microbes. Plants grow in and from soils, and plants directly or indirectly feed almost all life on Earth. 

Soils are among the great ecosystem service providers on earth. They prevent floods by transferring water slowly to streams and groundwater. They filter and remediate pollutants. They cycle and recycle nutrients and wastes, transforming them into biologically available forms, storing them away for later use, and preventing their leaching to ground and surface waters. Soils provide a habitat for a vast diversity of life. They take up and release important gases, including oxygen and greenhouse gases, a service called gas regulation. 

Many of these ecosystem services are being lost through the degradation and loss of soils. Many human activities degrade and pollute soils, lessening the ecosystem services provided by soils and making some soils and their runoff water harmful to our environment and human health. The conservation, restoration, and optimization of ecosystem services provided by soils is among the great challenges for humanity in the 21st century.

The clean-up of soils is among the great efforts being conducted by soil scientists around the world.

Is your soil alive? Or scantily breathing?

                                                                                                          BY- Yashashree Kar




Tags: Biology, Soil

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