Гранулометрический состав почв

Почва — сложная полидисперсная система, состоящая из четырех фаз: твердой (минеральные и органические частицы), жидкой (почвенный раствор), газообразной (почвенный воздух) и живой (почвенные организмы).

Твердая фаза почв и почвообразующих пород состоит из частиц различного размера. Отдельные частицы (гранулы) называются механическими элементами. В почве преобладают минеральные частицы, образовавшиеся при выветривании горных пород. Кроме минеральной части в почве содержатся органические частицы, происхождение которых обусловлено биологическими процессами; наличие небольшого количества органоминеральных фракций в почве связано с процессами взаимодействия минеральных и органических компонентов.

Частицы более 1 мм называют скелетом почвы, менее 1 мм — мелкоземом. В мелкозем входят: физический песок (частицы более 0,01 мм) и физическая глина (частицы менее 0,01 мм). В разных почвах содержание мелких и крупных фракций сильно варьирует.

Гранулометрическим составом почвы называют соотношение частиц различной крупности, выраженное в процентах. От размера почвенных фракций зависят не только физические, но и химические свойства почвы.

(Источник: http://www.zoodrug.ru/topic3558.html)

LESSON 9

Find in Text 9 English equivalents for the following words and expressions and memorize them.

1) когезивные свойства

2) адгезионные свойства

3) пропахивание (почвы)

4) уровень влажности

5) рыхлый, рассыпчатый

6) отвердевший, затвердевший

7) плотность почвы (плотность сложения)

8) пористость (порозность)

9) осушение

10) соответственно (т.е. в указанном порядке)

11) дренаж

12) вспучивание грунта от мороза

13) сдерживающий фактор

14) попеременное замораживание и оттаивание

15) водоёмы

16) осень (American English)

17) вечная мерзлота

18) фактически (НЕ «виртуально»!)

19) водоудержание

20) мульча

Translate the text from English into Russian.

TEXT 9

SOIL CONSISTENCE

Consistence is the resistance of the soil to deformation or rupture. It is determined by the cohesive and adhesive properties of the entire soil mass. Whereas structure deals with the shape, size, and distinctiveness of natural soil aggregates, consistence deals with the strength and nature of the forces between the sand, silt, and clay particles. Consistence is important for tillage and traffic considerations. Dune sand exhibits minimal cohesive and adhesive properties, and because sand is easily deformed, vehicles can easily get stuck in it. Clay soils can become sticky when wet, and thus make hoeing or plowing difficult.

Soil Consistence Terms

Consistence is described for three moisture levels: wet, moist, and dry. A given soil may be sticky when wet, firm when moist, and hard when dry. A partial list of terms used to describe consistence includes:

1. Wet soil-nonsticky, sticky, nonplastic, plastic

2. Moist soil-loose, friable, firm

3. Dry soil-loose, soft, hard

Plastic soil is capable of being molded or deformed continuously and permanently, by relatively moderate pressure, into various shapes when wet. Friable soils readily break apart and are not sticky when moist. Two additional consistence terms for special situations are cemented and indurated. Cementation is caused by cementing agents such as calcium carbonate, silica, and oxides of iron and aluminum. Cemented horizons are not affected by water content and limit root penetration. When a cemented horizon is so hard that a sharp blow of a hammer is required to break the soil apart, the soil is considered to be indurated.

DENSITY AND WEIGHT RELATIONSHIPS

Two terms are used to express soil density. Particle density is the average density of the soil particles, and bulk density is the density of the bulk soil in its natural state, including both the particles and pore space.

SOIL PORE SPACE AND POROSITY

The fact that mineral soils have a particle density and bulk density of about 2.65 and 1.3 g/cm3 , respectively, means that soils have about 50 percent total pore space or porosity. In simple terms, rocks without pore space are broken down by weathering to form mineral soils that have about 50 percent porosity. The pore spaces vary in size, and the size of pore spaces themselves can be as important as the total amount of pore space.

SOIL COLOR

Color is about the most obvious and easily determined soil property. Soil color is important because it is an indirect measure of other important characteristics such as water drainage, aeration, and the organic matter content. Thus, color is used with other characteristics to make many important inferences regarding soil formation and land use.

SOIL TEMPERATURE

Below freezing there is extremely limited biological activity. Water does not move through the soil as a liquid and, unless there is frost heaving, time stands still for the soil. A soil horizon as cold as 5° C acts as a deterrent to the elongation of roots. The chemical processes and activities of microorganisms are temperature dependent. The alternate freezing and thawing of soils results in the alternate expansion and contraction of soils. This affects rock weathering, structure formation, and the heaving of plant roots. Thus, temperature is an important soil property.

Location and Temperature

In the northern hemisphere, soils located on southern slopes have a higher temperature than soils on north-facing slopes. Soils on south-facing slopes are more perpendicular to the sun's rays and absorb more heat energy per unit area than do soils on northern slopes. This is very obvious in tundra regions where soils on north-facing slopes may have permanently frozen subsoil layers within the normal rooting depth of trees, whereas soils on southern slopes do not.

Large bodies of water act as heat sinks and buffer temperature changes nearby. In the spring and fall the temperature changes more slowly and gradually in the area adjacent to the Great Lakes than at locations further inland. Near these lakes in the spring, the temperatures of both air and soil increase slowly, which delays the blossoms on fruit trees and thereby reduces the hazard of late spring frosts. Killing frosts in the fall are delayed, resulting in an extension of the growing season. As a consequence, production of vine and tree fruits is concentrated in areas adjacent to the Great Lakes.

Permafrost

When the mean annual soil temperature is below 0° C, the depth of freezing in winter may exceed the depth of thawing in summer. As a consequence, a layer of permanently frozen soil, called permafrost, may develop. Permafrost ranges from material that is essentially all ice to frozen soil, which appears ordinary except that it is frozen and hard.

SUMMARY

Soil physical properties affect virtually every use made of the soil. Texture relates to the amount of sand, silt, and clay in the soil and structure relates to the arrangement of the sand, silt, and clay into peds. Texture and structure greatly affect plant growth by influencing water and air relationships. Soils that expand and shrink with wetting and drying affect the stability of building foundations. About one half of the volume of mineral soils is pore space. Such soils have a bulk density of about 1.3 g/cm 3 and 50 percent porosity. In soils with favorable conditions for water retention and aeration, about one half of the porosity is macropore space and one half is micropore space. Soil color is used as an indicator of organic matter content, drainage, and aeration. Soil temperature affects plant growth. Soil temperature is greatly affected by soil color, water content, and the presence or absence of surface materials, such as mulches. Permafrost occurs in soils with average temperature below freezing.

(H.D. Foth, Fundamentals of Soil Science)

Answer the questions.

1) How can soil be described in terms of soil consistence?

2) What is the difference between particle density and bulk density?

3) Why is soil colour important?

4) What are the most common colours of soil?

5) How does temperature affect soil?

6) What is the most suitable soil temperature for plant growth?

7) What is permafrost?

Match the synonyms.