- •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.
- •4. Soil texture.
- •2. Plant roots and soil relations.
- •3. Soil fertility and soil productivity.
- •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.
1.1. Composition and concentration of soil solution.
Soil solution concentration is usually not high, not exceeding a few grams per liter. Saline soils may be an exception and their solution may contain several dozen and even several hundred grams per liter. Mineral, organic and organic-mineral substances are present in soil solution in ionic, molecular and colloidal forms. Soil solution always contains some dissolved gases: CO2, O2, etc. According to K.K. Gedroiz, colloidal part may be within 1/4-1/10 and less of the total dissolved solids. Soil solution of organic and humic horizons of the profile are richer in organic compounds compared with those of the other horizons of the profile. In chernozemic, chestnut, greyzem and solonetzic soils, the amount of mineral components (carbonates gypsum and soluble salts) increases downward in soil profile. The most important anions in soil solution are: NO3-, SO42-, HPO42-, H2PO 42-, PO42-, etc. In saline soils, there is much of Cl-, SO42-, HCO3-, CO32-, Ca2+, Mg2+, Na+, etc. The pH of soil solution characterizes the active forms of soil acidity or alkalinity which considerably affect the chemical, physicochemical and biological processes occurring in the soil
as well as the growth and development of plants.
1.2. Osmotic pressure of soil solution.
Osmotic pressure of soil solution is very important to plant growth. If it is equals or exceeds the osmotic pressure of a cell juice there is no intake of water by the root and the plant dies. Osmotic pressure is dependent on the concentration, of the soil solution and the degree of dissociation of dissolved components in it. Saline soils have the highest values of osmotic pressure. Thus according to the data obtained by Gebhard (1928), the osmotic pressure of soil solution in chernozem was 2∙105 Pa while in solonchak (very saline soil) it was 13,6∙105 Pa. High osmotic pressure shortens the period of vegetation in wheat, delaying tillering and accelerating the formation of ears. Transpiration coefficient is lover and the protein content in grain higher. But the yield of grain may be drastically reduced.
1.3. Redox potential and redox processes in the soils.
Redox reactions in the soil are the result of a cycle started by photosynthesis. The soil reactions utilize the energy stored by photosynthesis, dispose of organic wastes, and produce the CO2 for additional photosynthesis. Redox reactions involving C, N and S are determined largely by the availability of electrons and are usually catalyzed by enzymes.
The major electron donors in soils are freshly fallen plant matter and soil organic matter (SOM). Other electron donors in soils besides organic carbon include the N and S in amino (-NH2) and sulfhydryl (-SH) groups and the ammonium ions. Soil microorganisms create other electron donors when oxygen is lacking in the soil.
Oxygen is the strongest electron acceptor in nature and therefore yields the most energy from oxidation. The solubility of oxygen in water is low (about 10 mg/l-1 at 250C). The oxygen demand on soils can exhaust the dissolved oxygen in a water logged soil in less than 24 hours. If oxygen is unavailable, soil microorganisms can utilize other electron acceptors. A tendency of a substance to donate or accept electrons is given by its electrode potential.
Eh characterizing the redox condition of a soil is in Ukraine expressed in mv. To obtain comparable data on the redox conditions in media with different pH, Clarc proposed an index of rH2:
rH2 =Eh/30+2pH.
rH2 over 27 is an evidence of the domination of oxidation. Reduction processes begin to prevail at rH2 <27. An intensive development of reduction processes in waterlogged soils may be characterized by rH2<20.
In normally wetted soddy-podzolic soils Eh fluctuates within 550-750 mV. In paddy rice and swamp soils it may be below 200 mv. Optimal conditions for nitrification are within Eh=350-500 mv. The reduction of Eh to 200-250 mv or even to 350-400 mv in podzolic soils with crude organic matter may cause the formation of excessive amounts of Fe2+ and Mn2+ in soil solution which may become toxic to plants.