Introduction

Soil science is a science of soils, their origin, properties, composition, geography, development, functioning in the environment; their rational use, conservation and improvement (reclamation).

It is almost unanimously believed by the scientific community of the world that the concept of soils as independent natural bodies was introduced and developed by V.V.Docuchaev (1846-1903) and his school of Russian soil scientists (A.P.Kostychev, M.M.Sibirtzev and others). Western Europe got to know about it by D.K.Glinka in a book published in German. Marbut’s translation of this book made the Russian concept of soil as a natural body easily available to the English-speaking world. Recognition of the relationships between soil features (особенность) and factors of soil formation (climate, vegetation, parent material, land forms, and time) was not limited to Russian scientists. In the United States, Hilgard had noted this association in a book published in 1860 (Jenny, 1961), and Coffey had recognized soils as natural bodies by 1912 (Kelloy, 1941). However, the development of the concept of soils as natural bodies with horizons that reflect the influences of soil forming factors, particularly climate & vegetation, may be credited to the Russians. Ukrainian Soil Science is traditionally genetic as it is based on the study of origin, development and evolution of soils which it inherited since being a part of Russian and Soviet Soil Science.

The book is designed for the students who have completed a year of college chemistry, including analytical, physical, and colloidal chemistry, fundamentals of geology and geomorphology, physics, and mathematics (calculus is not required). Our aim with this text is to help preparing the bachelors of Science in Ecology with a good understanding of the nature and properties of soils as viewed from their employment in ecology assessment.

LECTURE ONE.

General scheme of soil formation.

Study outline:

1. Factors of soil formation.

2. General scheme & processes of soil formation.

3. Morphological features of the soil profile.

4. Soil ecology.

1. Factors of soil formation.

Soil formation, or, using a more up-to-date term, soil genesis, deals with the factors & processes of soil formation. The formation of soil is the process of the interaction of five natural soil-forming factors: (1) climate, (2) organisms, (3) parent material, (4) topographic position or slope, & (5) time.

Role of climate in soil genesis. Climate greatly affects the rate of soil genesis. In areas that are permanently dry &/or frozen, soil does not form. The two most important components of climate are precipitation & temperature.

Precipitation effects. Water is necessary for mineral weathering, residue decomposition & plant growth. Water in excess of field capacity(surplas water) participates in the downward translocation of colloidal particles & soluble salts. The limited supply of water in deserts results in soils that tend to be alkaline, low in clay, OM content & CEC. Generally soils of the arid & subhumid regions tend to be fertile except for the limited ability of the soil microbes mineralize to SOM to supply available nitrogen. Where is sufficient water for only limited leaching, the carbonates tend to be moved downward only a short distance a form a zone or horizon of calcium carbonate accumulation (K layer). Increases in precipitation have been positively related with greater leaching of lime & greater depth to a K layer, development of soil acidity, weathering & clay content, & plant growth & OM content.

Temperature effect. Every 10°C increase in temperature increases the rate of chemical reactions approximately two times. Increased weathering & clay formation occur with an average increase in soil temperature.

The relationship between average temperature & plant grouth & accumulating of OM is complex. R.Volobuyev proposed a formula reflecting functional dependence of the content of soil humus on the hydrothermal factor (Hf),which characterizes the hydrothermal conditions depending on the annual precipitation (P) & mean annual temperature(T):

H_f=43.2 log P-T

This formula “works well” for the northern hemisphere. The forested soils of the southeastern United States contain only 60% as much OM as do the forested soils further north.

Role of organisms in soil genesis. Plants affect soil genesis by the production of OM, nutrient cycling, & the movement of water through the hydrologic cycle. Microorganisms play an important role in OM mineralization & the formation of humus. Soil animals are consumers & decomposes of OM but the most obvious role of animals appears to be that of earth movers. A most obvious effect of organisms on soil genesis is that caused by whether the natural vegetation is trees or grass. Thus the forested soils in Ukraine contain significantly less OM than grassland soils.

Role of parent material in soil genesis. Parent material has a great influence on the properties of young soils, including color, texture, structure, mineralogy & pH. Over time the effects of the parent material decrease, but some of them still persist in old soils. Consolidated rocks are not parent material but serve as a source of soil parent material. Soil formation unknot await the physical disintegration of hard rocks when granite, basalt, or sandstone are exposed to weathering. Most soils have developed from sediments that were transported by water, wind, ice, or gravity. Such may be colluvial, alluvial, fluvioglacial, glacial,& eolian deposits. Loesses are the most “favorable” parent material for any soil & it is a real benediction for 75% or so of Ukrainian soils. Organic deposits (peat) may be the parent material for organic soils.

Role of topography in soil genesis. Topography is the configuration of the surface of a local area of land. Differences in topography can cause wide variations in soils within the local distribution or disposal of the precipitation & determines the extent to which water tables influence soil genesis. Water-permeable soils on broad, level areas receive & infiltrate almost all of the precipitation. Soils on sloping areas infiltrate less than the normal precipitation, hence, there is runoff. Depressions & low areas receive additional water, making more water available for soil genesis than the normal precipitation. The effects of water relation on soil genesis are more pronounced in humid than in arid regions. Both the length & steepness of slope affect soil genesis. There is greater water runoff & soil erosion. The net effect is a retardation of soil genesis (Polupan M.I.). Many soils on sloping land may be in equilibrium in terms of erosion. Drainage is a measure of the tendency of water to leave the soil. Well-drained soils occur in the upper parts of the landscape. Poorly drained ones-in the low parts. They may be overwet & gleyed. A sequence of soils along a transect that differs because of topography is a soil catena. Topography, parent material, & time interactions may produce some very complicated soil cover.

Role of time in soil genesis. Soils are products of evolution & soil properties are a function of time or soil age. The relative age of a soil is expressed by its degree of development & not the absolute number of years, which expresses the absolute age of a soil. Soils have a life cycle that is represented by various stages of development. We understand what is mean by minimally, moderately, and intensively weathered soils. To study time us a soil-forming factor, the other soil-forming factors must remain constant, or nearly so. The rate of soil genesis is highly dependent on the nature of the soil-forming factors. In some situations, soil genesis is rapid, whereas is others, soil genesis is very slow. Some soil features or properties develop quickly, but the development of other properties requires much more time.

Human being as a soil-forming factor. One of the most obvious & early effects of human activity on soil has occurred at campsites & villages. Organic residues have been added to the soils. The use of land for agriculture, forestry, grazing, & urbanization has produced extensive changes in soils, including soil erosion, drainage, salinity development, depletion & addition of OM & nutrients, compaction & flooding. Human beings have affected many soils through earth moving. Considering the way human beings multiply & how the demands for food, bibre, recreation & luxury items grow, the soils should be considered a nonrenewable natural resource like the fossil sources of energy.