Text 4 Soil Physics

4.1 Read the following international words and translate them: structure, architecture, horizon, configuration, cemented, microscope, complex, section, plus, mathematically, erosion, problems, operations, grouping, vertical, contrast, system, selection.

4.2 Say it in Russian: the movement of air, water and solutes, soil classification, gravels, stones, iron oxides, plant roots, bulk density, particle density, high density, solonetz soils, little porosity, root growth, chemical conditions, salinity, sand silts, clay, fine textured soils, coarse textured soils, iron compounds, correct irrigation system, ground water quality.

4.3 Read and translate the text with the help of a dictionary.

S oil physics properties are extremely important from both agriculture and engineering standpoint. The way in which a soil is put together, or its architecture, is related to its structure which in turn is a reflection of texture, aggregation and porosity. The movement of air, water and solutes through the soil is dependent on the spaces and their configuration among the soil particles. This will also affect soil temperatures and the soil’s ability to store water. Physical properties such as colour, texture and structure are used in soil classification, particularly in horizon definitions. All these properties will affect how easy the soil will support living organisms or how easy the soil will support a building.

Soil Separates Soils are made up of a mixture of particles ranging from clay size of less than 2 mm to gravels and stones. Smaller particles are often cemented together by organic matter, iron oxides. If we remove the cementing material and disperse the particles in water we can separate the individual particles by sedimentation. The coarse particles settle first, the fine particles last.

Density and Porosity Bulk density is the mass of one cm³ of the soil which includes both solid plus the voids among particles or the pore space. The size of soil particles and how they are clumped together or aggregated largely determines the bulk density and porosity. Solonetzic soils have severe structural problems due to high sodium salts in their parent material. The B horizons of these soils have a high density and little porosity characterized by the round top structure that is almost impossible for plant roots to penetrate, operations such as clear cutting forests, heavy field equipment and erosion can lead to increases in bulk density and subsequent reduction in porosity.

Structure The term structure refers to grouping of the primary soil particles into secondary clumps or aggregates – often called peds. Structure is important to components that flow such as water, air, heat, nutrients. Chemical conditions such as salinity can severely affect structure.

Texture Soil texture is a reflection of the distribution of particle size fractions in soils or the relative amounts of sand silts and clay. Fine textured soils contain more clay size minerals and have relatively high porosity but the pores are small and often discontinuous. In contrast, coarse textured soils contain sand sizes minerals and have more porosity but bigger pores that are connected.

Colour The colour of soil surface horizons is related to how much organic matter is present. In sub surface horizons mineral composition becomes important. Accumulations of oxidized iron compounds give red colours, loss of organic matter and iron compounds gives light coloured grey horizons. Red and brown mottled horizons are indicative of reduced conditions or water logged soils.

Soil Water Soil water holding characteristics are important for dry land farming, selection of the correct irrigation system, irrigation scheduling, crop selection, and ground water quality.