Text 6 Living Soil

6.1 Read the following international words and translate them: based, physical, evolutionary, fauna, flora, organisms, limits, diameter, microscope, ecosystem, reaction, production, structure, parasitic, factor, zone, millimeters, microb, laboratory, classification, system, cycle.

6.2 Say it in Russian: soil biology, fungi, macro-, meso-, micro-, magnifying glass, a predatory cycle, beneficial organisms, to improve soil structure, small animals, rhizosphere, to fix nitrogen, the soil air, to decompose organic matter, the weight, aeration, to resist erosion, below ground portion.

6.3 Translate the following chains of nouns: plant root cells, soil sample, size group, complex food chain, organism population, animal residues, soil formation, root mass, crop yields, soil ecosystem, soil structure.

6.4 Read and translate the text with the help of a dictionary.

The study of living component of soils is called Soil Biology. The classification (taxonomy) and study of soil organisms is largely based on physical similarities.

In this section we will take a simple approach to study soil organisms, dividing them first into two groups: Animals (fauna) and Plants (flora).

Next we break down these groups further into more manageable divisions based on size of the organism: large, medium, and small or Macro- Meso- and Micro-. We have to define the limits for each size group. Macro organisms are considered to be larger than 2 mm in diameter. Meso organisms are between 2 mm and 0.2 mm in diameter. Micro organisms are less than 0.2 mm.

When you study soil organisms try to understand not only the individual organisms but also the complex interactions and processes that make them part of the soil ecosystem. Particularly important is the complex food chain or more correctly the food web in which energy passes from primary producers (plants) to consumers in a predatory cycle that forms a crucial part of life on our planet.

Many soil organisms are beneficial but others are devastating to crops and animals. Beneficial organisms take part in many physical and chemical reactions that improve soil structure, break down organic matter and cycle nutrients. Others, however, such as the tiny nematode, a worm, less than 0.1 mm long can cost farmers billions of dollars, every year, in lost production.

Soil Fauna Important soil macrofauna include:

1. Vertebrates – gophers, mice, ground squirrels

2. Arthropods – insects

3. Annelida – enchytraeid worms

4. Mollusca – slugs and snails

There are a number of small animals that burrow and live in soils including mice, moles, ground squirrels and prairie dogs or gophers. In their search for food and nest building, these animals dig and burrow, bringing tons of subsoil to the surface.

Important soil mesofauna include:

1. Arthropods – mites, collembola

2. Annelida – earthworms

Many of the mesofauna are important for mixing the soil and breaking down the larger plant residues.

Soil microfauna include:

1. Nematoda – mites, collembola (spring tais)

2. Rotifera – rotifers

3. Protozoa – amoeba

Unfortunately, a large number of these microfauna are parasitic and can cause devastating effects on crop yields.

Soil Flora The most important members of our soil macroflora group are the living plants or more importantly below-ground portion or the roots. Vegetation is an important factor in soil formation.

For a few millimeters around the active roots is a special zone called the rhizosphere. Root exudates create a rich environment for the growth of microorganisms. The activity of the microorganisms in turn fixes nitrogen from the soil air, dissolves soil minerals and decomposes organic matter to enhance the ability of roots to pick up essential nutrients.

Although very small, microorganisms have an importance in soil which far outweighs their size. They decompose plant and animal residues, synthesize humus, cycle nutrients such as carbon and nitrogen. The chemical by-products of microbial reactions bind together soil particles into stable aggregates that resist erosion.

Although not directly associated with plant roots actinomycetes and algae are also important fixers of atmospheric nitrogen that can be used later by soil organisms. Not all microorganisms are beneficial. Some organisms are harmful to plants and humans. Did you know that some of the most deadly bacteria come from soil such as microbes responsible for tuberculosis, anthrax, leprosy and cholera?

Food web The survival of life in our planet depends on ultimately on the cooperation and interactivity of the various organisms. Especially important is the so called food chain or more accurately the food web. Energy is passed down the food chain from the primary producers such as plants to primary consumers such as ruminant animals to secondary and tertiary consumers which are predators. The body of one organism becomes food for another in a very complex interaction.