The topsoil which is desirable for the growth of plants is eroded because of human activities like making of homes, roads, buildings and city expansions. Soils serve as the only medium for plant growth. The Ethiopian highlands suffer from severe land degradation, including erosion. Soil water is important for three special reasons: The presence of water is essential for the all life on Earth, including the lives of plants and organisms in the soil. Movement through a sandy layer is very sluggish at intermediate and high tensions. Free energy of soil water is affected by: (i) Matric (solid) force i.e., the attraction of the soil solids for water (adsorption)— which markedly reduces the free energy (movement) of the adsorbed water molecules. This type of soil are formed in nature under many plant covers and after forest fires, which tend to vaporize oils and resins and drive them into the soil where they coat the soil particles and cause them to resist wetting. Available water is defined as that portion of water which is retained in the soil between field capacity (-1/3 bar) and the permanent wilting coefficients (-15 bars). Hydrogen of water bond strongly to these surface oxygen atoms by adhesive bonding (the attraction of unlike molecules). Tortuosity (zig-zag path) of soil pores and entrapped air in the soil, Soil pores are not continuous, straight and uniform like that capillary glass tubes. When ions are hydrated, a large amount of energy is released and this is known as heat of solution. Some soil moisture characteristics. The phenomenon of surface tension is generally evidenced at water—air interfaces and it may be defined as the forces in dynes acting at right angles to any line of 1 cm length in the surface. While there are some plants that can live in water or air, most plants need to be rooted to the ground. For optimum water used, it is vital to know how water moves into and through the soil, how the soil stores water, how the plant absorbs it, how nutrients are lost from the soil by percolation, and how to measure soil water content and losses. 7.2.). Fine texture soils like clay, clay loam soils contain more hygroscopic water as compared to coarse textured sandy soils. The soil water potential is a combination of the effects of the surface area of soil particles and small soil pores that adsorb water, matric potential Ψm) the effects of attraction of ions and other solutes for water, solute or osmotic potential (Ψs) and the atmospheric or gas pressure effects, pressure potential (Ψp). Potential represents the difference in free energy levels of pure water and of soil water. Soil water, its changes over time and management are of interest to geo-technicians and soil conservationists with an interest in maintaining soil stability. Various potentials can be written as follows: Most of the productive soils have no depth of water standing on it and can be written as follows: Therefore, among all potentials matric potential (Ψm) is the most important and dominant for most soils. Adsorbed water always less free energy (less ability to do work) than water in the pool (zero potential). It is the soil that provides nutrition to this plant life. Maximum water holding capacity is defined as the capacity of a soil to retain water is exceeded. Water plays a … For photosynthesis, plants require carbon dioxide and water. The retention and movement of water in soils, its uptake and translocation in plants and potential evapotranspiration etc. The soil is the best natural resource available to us. Soil Porosity Many important soil processes take place in soil pores (the air or water-filled spaces between particles). The amount of hygroscopic water varies inversely with the size of soil separates. It is vital for our survival on the earth. This is mainly attributed to the greater surface area and a large number of micro-pore spaces present in such soil. Consequently there is a net down-ward (in ward) force on the surface molecules, resulting in sort of a compressed film at the surface. Factors Affecting Gravitational, Capillary and Hygroscopic Water: Soil texture and structure are two main factors that affect the amount of gravitational water. At equilibrium, the algebraic sum of all forces would be zero. At the surface, the attraction of air for the water molecules is much less than that of water molecules for each other. Keeping all other factors equal, deep soils will have greater available water holding capacities as compared to shallow depth soils. The comparative available water holding capacities in relation to water content (inches/foot of soil) are also being shown by the figure 7.8. In fact, the soil water is a great regulator of physical, chemical and biological activities in the soil. Fig. Capillary water is retained on the soil particle by force of attraction between soil particles and water molecules (Fig. This accounts for the polarity of water and therefore, water is most important for carrying out many reactions in soils and plants. The hydrogen’s of water are also attracted (bonded) to oxygen of other water molecules, including those already adsorbed on to the soil particle surfaces. It is important to retain this water and manage it carefully if the seed is to germinate. Whereas, spheroidal soil structure helps to improve the movement of gravitational water by increasing its rate of infiltration and percolation. Viele übersetzte Beispielsätze mit "soil water" – Deutsch-Englisch Wörterbuch und Suchmaschine für Millionen von Deutsch-Übersetzungen. Different Forces of Retention 4. There is a definite relationship between moisture retention and its utilization by plants. An additional effect of the position of the water (such as being elevated) compared to the reference state (the reference free energy state = 0 and is at a specified elevation) is called the gravitational potential (Ψg). 7.6. Soil support roots and keep them erect for growth. The finer the texture of a soil the larger the quantity of capillary water it holds. The soil water content at the stage where the plant dies, is called permanent wilting point. The H of water in soils may bond to oxygen ions of soil mineral surfaces, thereby holding the water tightly to soil. The bottom line is that soil is essential for life because it provides the medium for plant growth, acts a filtration system for surface water, maintains the balance of atmospheric gases, stores carbon, and is a habitat for several organisms. Soil provides important ecosystem services that support different processes in nature, including nutrient cycling and gas exchange. There are various factors to be considered that affect the amount of capillary water in soil namely, soil texture, soil structure, surface tension, organic matter content, size of capillary pores in soil, tortuosity (zigzag path) of capillary soil pores etc. Good soil drains excess water well without drying out too quickly. The soil water content at the stage where the plant dies, is called permanent wilting point. Therefore, there is need for soil diagnosis and that’s why soil sampling is critical. 2.4 Available water content. Soil water potential can be measured in two units at varying energy levels in soil. It is used to clean instruments and for hydrotherapy and dialysis. As the fineness of texture increases, there is a general increase in the amount of available water. 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