Soil composition and properties.
Soil is a fertile superficial layer of Earth crust, which emerges from biospheric and atmospheric impact on lithosphere. First scientific definition of soil was given by an originator of soil science V. Dokuchayev: "Soil is a 'daylight' or external layer of geological material exposed to the natural overall impact of water, air and various living and dead organisms".
Dokuchayev has found out that soil is not only a constituent part of natural landscape, but its product, as well. His thesis that all soils at the Earth surface emerge as a result of an "extremely complex interaction of local climate, plant and animal bodies, composition and structure of mother bed, lay of land, and, finally, age of land", has become a cornerstone statement of soil science.
Soil rests on lithospheric surface. But it would have been a mistake to treat it as a mineral formation, since it has plant and animal bodies as permanent residents in it. And at the same time it should not be treated as a product of sole plant and animal bodies' activity. Soil is a specific naturalistic formation, an individual natural body, constantly changing in space and time. This complex natural body owes its existence to the interaction of soil-formation factors.
Soil colour tells us about its composition: shadow (gray and brown) tones result from humus substances; ocherous, yellow, orange and red tones result from iron and manganese oxides; white stains, adhesions and 'moulds' result from lime.
Soil consistency means its void content and density. Depending on the size and form of vesicles, it can be firm (with visible pores), finely porous or macroporous, honeycombed, cavernous, fissured.
Soil pedality means its flocculation capacity. Every type of virgin soil has its own structure.
Soil neoformation is a concentration in soil voids of various substances, having emerged as a result of soil formation process and allied with the soil. Neoformations include mottles, blooms, crusts, adhesions, cutans, streaks, heads of different compounds, worms' and larvae's coproliths, mole casts of big shrews.
Soil inclusion is a foreign body, which is not allied with soil layers: boulders and gravel, shells and animal bones, artefacts. Inclusions help to determine the time of soil formation.
Soil texture is a content of particles of different size. The easiest way to determine soil texture is as follows. Moisten soil sample to a paste consistency and knead with fingers; then roll out the well-kneaded soil on the palm into a 3-mm cord and fold it into a ring with a 3-cm diameter.
- if cord is not formed, soil is sandy;
- if cord is not consistent, soil is sandy-loam;
- if cord falls into fractions, soil is lightly loam;
- if ring breaks, soil is medium loamy;
- if cord folds into a ring and the ring chaps; soil is heavily loam;
- if cord folds into a ring and the ring does not chap, soil is clayey.
When analysing soil profile, besides the above-mentioned morphological properties, analyst should consider soil humidity and density. Below is the simplified soil humidity score:
- wet soil - weeping when digging;
- humid soil - a sheet of paper put on the soil gets wet immediately;
- fresh soil easily smears and feels a cool paste;
- tight soil gives up dust and feels dry.
Soil formation factors changing in space and time produce many types of natural soils.