- •Department of Soil Science & Soil Conservation
- •Introduction
- •2. General scheme & processes of soil formation.
- •3. Morphological features of the soil profile.
- •4. Soil ecology.
- •Study outline:
- •1. Soil definition and the factors of plant growth.
- •2. Plant roots and soil relations.
- •3. Soil fertility and soil productivity.
- •4. Soil texture.
- •1. Sources and composition of som.
- •2. Residue decomposition and humus formation.
- •3. Agronomical and ecological roles of som.
- •4. Maintenance and balance of som.
- •2. Nature and properties of soil colloids.
- •3. Pole in soil genesis and soil productivity development.
- •4. Types and practical significance of soil absorbing capacity.
- •2. Soil Properties as Effected by Exchangeable Cations.
- •3. Soil Acidity & Acid Soil Amendment.
- •4.Soil Alkalinity & Sodic Soil Amendment.
- •5. Soil Buffer Capacity & Significance of Soil pH.
- •2. Managing soil structure.
- •3. Particle density and bulk density.
- •4. Soil porosity and aeration porosity.
- •5. Mechanical properties of mineral soils and their management.
- •2. Soil Water Movement.
- •3. Plant and Soil Water Relations.
- •4.Soil Water Regime.
- •6. Soil Water Management.
- •1.1. Composition and concentration of soil solution.
- •1.2. Osmotic pressure of soil solution.
- •1.3. Redox potential and redox processes in the soils.
- •2. Soil air, a gaseous phase of the soil.
- •2.1. Soil air composition and properties.
- •2.2. Plant requirements to soil aeration.
- •3. Management of soil redox and aeration regimes.
- •1. Soil temperature & modes of energy transfer.
- •2. Conduction of heat in soil. Heat-related soil properties.
- •3. Thermal conductivity of soil.
- •4. Thermal regime of soil profiles &its control.
- •2. Principles of soil cover zoning in Ukraine.
- •3. Soil Zoning in the Mountain regions.
- •4. Fao nomenclature of soils.
- •2. Soddy Podzolic and Soddy Podzolic Gleyed soils.
- •3. Soddy soils.
- •4. Bog and Peat soils.
- •5. Practices of soil management in Ukrainian Polissya.
- •2. Grey Forest and Podzolized soils.
- •3.Chernozems of the Steppe Zone.
- •2. Dark chestnut and chestnut soils.
- •3. Salt-affected soils.
- •4. Practices of soil amendment and land use improvement in the arid steppe zone.
2. Soil Water Movement.
“Water runs downhill”. So it is from regimes of higher energy water to regime of lower energy water. The driving force for water movements is the difference in water potentials between two points. The velocity of water flow is also affected by the soil’s ability to transmit water or the hydraulic conductivity,(K).Water flow through large pores is faster than through small pores. Flow is faster when the conductivity is greater. The velocity of flow, V , is equal to the water potential gradient (t), times the hydraulic conductivity: V=Kt. The conductivity of a soil is analogous to the size of the door to a room. The larger the door, the greater the speed at which people can go in or out. Conductivity is closely related to pore size. Water flow in a pipe is directly related to the fourth power of the radius. The larger pores give the sandy soils a greater ability to transmit water ( a greater conductivity) when saturated as compared to clayey soils. The largest pores are emptied first, followed by the pores of decreasing site. K (hydraulic conductivity) is closely related to soil water content: K decreases with decreasing soil water content.
How does water move in saturated soil? The quantity of water, Qw, that will flow through a soil ( or a pipe) depends on the cross section area, A, and the time of flow, t. Therefore, Qw=Kh/dAt, d being distance of flow through the soil, h being the difference in water potentials between two points ( the head). This equation is named after Darcy. According to Darcy’s equation, if the distance of water movement through soil is doubled, the quantity of water flow is halved (!). The further soil is from the drain lines, the longer it will take for water to exit the soil.
How does water move in unsaturated soil? If water is allowed to drain from a saturated soil, water leaves the soil first and most rapidly via the largest pores. Then water movement shifts to smaller and smaller pores. Hydraulic conductivity and the rate of drainage rapidly decrease. Gravity is always operating. After field capacity is attained, metric forces control water movement. Unsaturated hydraulic conductivity decreases rapidly when plants absorb water and soil becomes drier than field capacity.
3. Plant and Soil Water Relations.
Plants use large quantities of water. The water-supplying power of soils is related to the amount of available water a soil can hold. The available water is the difference between the amount of water at field capacity (-30 Kpa or –0.3 bar) and the amount of water at the permanent wilting point (PWP) (-1.5oo Kpa or – 15 bars). Soils high in silt (silt loams) tend to have the most optimum combination of surfaces and pores.
Plants play a rather passive role in their use of water. Water loss from leaves by transpiration is mainly dependent on the environment. Soil moisture may be determined by gravimetric, tensiometric, resistance measuring, and neutron scattering methods. The gravimetric method is one of the most commonly used. How does water vapor move in the soil? Relative humid of the soil air is maintained saturated with water vapor so long as the moisture content is not below that of hygroscopic coefficient. At this tension (-31 atmosphere) and less water is free to maintain humidity at saturation.
Transpiration ratio ranges from 100 to 500 for crops in humid region and almost twice as much for those of arid climates. Some plants shed their leaves during periods of extreme water. With each passing summer day, water moves more slowly from soil to root as soils dry. The availability of the remaining water decreases. This encourages root extension into soil devoid of roots where water potential is higher and water uptake is more rapid.
Most plants cannot tolerate the low oxygen levels of water-saturated soils. Water saturation kills many kinds of plants. These plants experience some increase in plant growth from saturation to near field capacity. As soils dry beyond field capacity, increased temporary wilting during the daytime causes a reduction in photosynthesis. Plant growth tends to be at a maximum when growing in soil near field capacity.
Water uptake is important for nutrient uptake. An increased flow of water increases the movement of nutrients to roots. Droughts reduce both water and nutrient uptake. Fertilizers increase drought resistance of plants.