3. Thermal conductivity of soil.

Thermal conductivity, designated K, is defined as the amount of heat transferred through a unit area in unit time under a unit temperature gradient.

The thermal conductivities of specific soil constituents differ very markedly:

Quartz	21 mcal/cm sec oK
Other minerals (average)	7
OM	0.6
Water	1.37
Ice	5.2
Air	0.06

Hence, the space-average (macroscopic) thermal conductivity of a soil depends upon its mineral composition and OM content, as well as on the volume fraction of water and air. Since the thermal conductivity of air is very much smaller than that of water or solid matter, a high air content (or low water content) corresponds to a low thermal conductivity.

Average thermal properties of soils:

Type	Porosity	Volumetric Wetness	Thermal conductivity 10-3cal/cm·sec·0c	Volumetric heat capacity cal/cm3 oC
Sand	0,4 0,4	0,0 0,	0,7 4,2	0,3 0,5
Clay	0,4 0,4	0,0 0,2	0,6 2,8	0,3 0,5
Peat	0,8 0,8	0,0 0,4	0,14 0,7	0,35 0,75

The factors which affect thermal conductivity (K) are the same as those which affect the volumetric heat capacity C_v.

4. Thermal regime of soil profiles &its control.

In nature, soil temperature varies continuously in response to the ever-changing meteorological regime acting upon the soil-atmosphere interface. That regime is characterized by a regular periodic succession of days and nights and nights of summers and winters. Yet the regular cycles are perturbed by irregular episodic phenomena (cloudiness, cold waves, warm waves, rainstorms and periods of drought).

In Ukraine the thermal regime of the soil is understood as a set of phenomena of the input, flow, and losses of the heat by the soil. It is estimated by the sums of soil temperatures at the depth of 20cm. A quantitative expression of this regime is the heat balance of soils which consist of the gains and losses of heat energy. Solar radiation received at the soil surface is partly reflected back into the atmosphere (albedo) and partly absorbed by the soil surface.

A dark-colored soil and light- colored-quartz sand may absorb about 80 and 30 % of the incoming solar radiation respectively. Heat is lost from the soil by: (1) evaporation of water, (2) radiation back into the atmosphere, (3) heating of the air above the soil and (4) heating of the soil. For the most part the gains and losses balance each other. But during the daytime or in the summer, the gains exceed the losses, whereas the reverse is true for nights and winters. In the temperate regimes the soils become very cold in winter and planting dates in the spring depend on a large rise in soil temperature. In general, sandy soils warm more quickly and allow earlier planting that do fine-textured soils, because sands retain less water and heat up faster. Location should also be taken into account. In the northern hemisphere, soils located on southern slopes have a higher temperature than soils on north-facing slopes.

Control of soil temperature. Two practical steps can be taken to change soil temperature. Wet soils can be drained to remove water, and mulches can be applied on the surface of the soil to alter the energy relationships. When used for agriculture, wet soils are drained to create an aerated root zone. The removal of water also causes the soil to warm more quickly in the spring.

A light-colored organic matter mulch, such as straw, will tend to lower soil temperature because (1) more solar radiation will be reflected and less absorbed, (2) the water content of the soil will tend to be greater because more water will infiltrate. The mulch will, however, tend to increase soil temperature because the mulch tends to: (1) reduce loss of heat by The mulch will, however, tend to increase soil temperature radiation and (2) reduce water evaporation from the soil surface, which requires energy. The next effect, however, is to reduce soil temperature in the spring. Crop residues left on the soil surface promote cooler soils in the spring and tend to result in slightly lower corn yields. A black plastic mulch increase soil temperature because it increases absorption of solar radiation, reduces heat loss by radiation and reduces evaporation of water from the soil surface. Black mulches have been used to increase soil temperatures in order to produce vegetables and melons for an earlier market.

LECTURE TEN.

General outline of soil classification and taxonomy.

Study outline:

1. Soil classification.

2. Principles of soil cover zoning in Ukraine.

3. Soil Zoning in the Mountain regions.

4. FAO nomenclature of soils.

1. Soil classification.

Classification schemes of natural objects seek to organize knowledge, so that the properties and relationships of these objects may be remembered and understood for some specific purpose. Most soil classification schemes have been developed on a native basis. The most suitable for international purpose is the soil classification and nomenclature developed by the soil and agricultural organization (FAO) of the United Nations

Soil vary from place to place in many profile characteristics. Each soil is a three-dimensional individual (pedon) which should be identified and classified in the field. Polypedons are mapping units in a large-scale soil survey. Each pedon may vary in size, say, from 1 to 10 sq.meters.

“Pedon” in Greek means “ground”. It is the smallest volume that can be called “a soil”. Because of its very small size, a pedon obviously can not be used as a basic unit for a workable field soil classification. A group of pedons closely associated in the field and similar in their properties are of sufficient size to serve as a classification unit. Such a grouping approximates what has been called a soil series in old and new comprehensive American systems of soil classification. Ukrainian system is very much different. It is genetic, geographic and historic in its essence. Ukrainian system of soil classification is based on the concept of soil as a natural body integrating the accumulative effects of climate, vegetation and other soil forming factors acting on surficial materials. This concept was introduced by Dokuchaev about 1880, developed by other Russian soil scientists, and proclaimed to western Europe by Glinka in 1914. Classification systems based on the inherent properties of the objects classified are called Natural or Taxonomic systems.

Up-to-date Ukrainian system of soil classification includes the following taxonomic units: (1) class, (2) type, (3) subtype, (4) genus, (5)species, (6) variety, and (7) lithologic series. The soils of Ukraine are divided into two classes: (1) zonal soils (bioclimatogenic), (2) azonal soils (biolithohydrogenic). Roughly the characteristics of zonal soils are determined primarily by the climate and vegetation. As the name zonal indicates, these soils are of such wide expanse as to be more or less regional in extent. Azonal soils, regardless of climate and vegetation, reflect the influence of some local condition such as poor drainage or alkali salts, or are without proper horizon differentiation. Most soils developed on recent alluvial deposits are azonal ones. Much remains to be elucidated here, especially in understanding the difference between azonal and intrazonal soils.

Soil type is the basic, fundamental taxonomic unit. The soils belonging to the same type were formed under similar hydrothermal conditions, under typically uniform plant associations, in parent materials of similar mineralogical composition and endowed with a similar type of soil profiles, close level of soil productivity and the same type specific set of soil (and land) management practices.

Soil subtypes allow to decipher the content of soil type and include the soils that, in addition to type-specific, possess some properties characteristic of the other soil types. Subtypes are the intermediate links between the type and they reflect the nondiscrete nature of soil cover.

Soil genues (or genii, which is more Latin) are identified within the subtype by a set of genetic (connected with origin) soil properties caused by the specific features of a parent material, ground water composition or the properties preserved from the preceding phase of a pedogenesis. The classification system takes into account the presence or absence of carbonates, soil acidity, gleying, depth of salinity or sodicity, the presence of claypens, skeletal fragment or the features acquired by the soils as a result of management, etc.

Soil species characterizes the extent of development of typical, subtypical, genial, and lithologic soil properties. It takes into account the depth of humus-containing horizons, OM content, and the extent of soil development or degradation (erosion, salinity, sodicity, carbonate depth, etc).

Soil variety reflects soil texture.

Soil lithologic series are determined by the parent material of a soil and occasionally it also takes count of the material which is not parent but immediately underlies the horizons of soil profile.