Geoscience Reference
In-Depth Information
quantity of enzymes respond to soil management changes long before other soil
quality indicator changes are detectable. The detection of various types of enzymes
and their relative amounts is a practical and objective tool for classifying soil
quality.
4.5
Algae
Algae differ from the micro-edaphon mainly by their existence either as single-cell
or multicell organisms and by their ability to convert the radiation of the sun into the
chemical energy utilized in all their life processes. They exist at soil depths repeat-
edly penetrated by rays of sunlight with their maximum numbers occurring at or
very close to the soil surface. Their numbers vary between 100 and 3 million per 1 g
of soil. In other words, on a land area of 1 ha, the soil is endowed with 0.2-1.5 tons
of algae. Sometimes they are distinctly visible as a greenish or bluish fi lm on top of
the soil surface. With water being essential for their existence, families of algae are
categorized on the basis of optimal or specifi c ranges of soil water content. Algae
are known as the pioneers who start the weathering of rock surfaces, often in a sym-
biotic relationship with fungi and lichens. They produce various slimes by which
individual soil particles are glued together into bigger aggregates which resist being
destroyed by water, raindrops, or water fl owing on the soil surface after the melting
of snow, a heavy rain, or an intentional irrigation.
Through photosynthesis, soil algae facilitate the aeration and oxygenation of
both submerged and un-submerged soil environments by liberating large quantities
of oxygen directly into the soil profi le. In un-cropped soils, they are especially help-
ful checking the loss of nitrates through leaching and drainage.
4.6
Zooedaphon
Microfauna
are the most abundant portion of the soil animal kingdom. They are
dominantly protozoa, and in addition to them there are also rotifers and in lesser
extent tiny nematodes. Their sizes range roughly between 2
m and 0.2 mm, but
they can grow as large as 1 mm. Within a column of soil having a surface area of
1 m
2
, we fi nd from 10 million up to 10 billion protozoa, and under favorable condi-
tions their mass may reach up to 100 g/m
2
. They gain their life energy not just from
the decomposition of plant residues and dissolved organic matter in soil water. They
absorb food through their cell membranes, and some as amoebae and fl agellates
also feed on bacteria. They surround food and engulf it. Others have openings simi-
lar to mouth pores into which they sweep food. All protozoa digest their food in
stomach-like compartments called vacuoles. In this way, they select and rejuvenate
the population of soil bacteria. Many parasites that affect human health or the
economy of agricultural production of food are fl agellates. The mass of nematodes
μ
