WATER-The Substance of Life

1. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology WATER-The Substance of Life • Limits Kinds and Amounts of Vegetation on Earth • Limits Growth of Cities and Kinds of Industry

2. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology EARTH’S WATER SUPPLY • 70% of Earth’s Surface • covered by water • 97% of Earth’s water supply in oceans • Ice at Polar Caps next most abundant supply (>2%) • Groundwater next most abundant supply (~0.5%); approximately 50% of ground water is > 0.5 miles deep • Fresh water in lakes, ponds and streams ~0.008% • Soil and atmospheric water ~ 0.001% • Biological water ~0.0001% • Average annual rainfall on land ~ 30 inches

3. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Precipitation Soil-Air Interface Vadose Zone Evaporation Portion of aquifer where pore spaces are occupied with water and air (unsaturated zone) Applications of soil physics are crucial to sustainable use of natural resources for agricultural and other land uses Soil-Water Interface Capillary fringe zone Ground water

4. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology تبخیر و تعرق نزولات جوی آبیاری نفوذ روان آب ذخیره در خاک نفوذ عمقی جریان داخلی عمق خاک

5. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Precipitation/Evaporation • P/E>0.75= Humid (Forests) • P/E >0.5= Sub-Humid (Mixed Forest and Grasslands) • P/E >0.25= Semi-Arid (Mixed Grasslands and Semi-Deserts) • P/E <0.25= Arid (Deserts)

6. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Soil Water Relationships

7. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology • Bulk Density (b) • b = soil bulk density, g/cm3 • Ms = mass of dry soil, g • Vb = volume of soil sample, cm3 • Typical values: 1.1 - 1.6 g/cm3 • Particle Density (p) • P = soil particle density, g/cm3 • Ms = mass of dry soil, g • Vs = volume of solids, cm3 • Typical values: 2.6 - 2.7 g/cm3

8. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology • Porosity () • Typical values: 30 - 60%

9. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Water in Soils • Soil water content • Mass water content (m) • m = mass water content (fraction) • Mw = mass of water evaporated, g (24 hours @ 105oC) • Ms = mass of dry soil, g

10. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology • Volumetric water content (v) • V = volumetric water content (fraction) • Vw = volume of water • Vb = volume of soil sample • At saturation, V =  • V = As m • As = apparent soil specific gravity = b/w (w = density of water = 1 g/cm3) • As = b numerically when units of g/cm3 are used • Equivalent depth of water (d) • d = volume of water per unit land area = (v A L) / A = v L • d = equivalent depth of water in a soil layer • L = depth (thickness) of the soil layer

11. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Volumetric Water Content & Equivalent Depth (cm3) Equivalent Depth (cm3) (g) (g)

12. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Volumetric Water Content & Equivalent DepthTypical Values for Agricultural Soils Soil Solids (Particles): 50% 0.50 in. 1 in. Very Large Pores: 15% (Gravitational Water) 0.15 in. Total Pore Space: 50% Medium-sized Pores: 20% (Plant Available Water) 0.20 in. Very Small Pores: 15% (Unavailable Water) 0.15 in.

13. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Water-Holding Capacity of SoilEffect of Soil Texture Coarse Sand Silty Clay Loam Dry Soil Gravitational Water Water Holding Capacity Available Water Unavailable Water

14. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Soil Water Content Soil Moisture Content Water that may be evaporated from soil by heating at 1050C to a constant weight mass of water evaporated (g) Gravimetric moisture content (w) = mass of dry soil (g) volume of water evaporated (cm3) Volumetric moisture content (q) = volume of soil (cm3) bulk density of soil q = w * density of water mass of dry soil (g) Bulk density of soil (r) = volume of soil (cm3)

15. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Soil Moisture Content: Methods of Measurement • Difficulties encountered for accurate moisture measurement in the field: • Soils are highly variable • Soil moisture is highly dynamic (spatial temporal variability) • Plant water uptake is highly variable depending upon the stage of growth • State of growth is again dependent upon nutrient application, water availability, pests etc. • Chemicals present in the soil can make measurements unreliable • Costs involved

16. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Methods for soil water content Direct method (Gravimetric; Thermogravimetric) Indirect methods Electrical properties Acoustic method Thermal properties Chemical methods Radiation technique -Neutron scattering -g- ray attenuation Methods of soil water content determination Electrical Conductance Dielectric constant TDR - Gypsum blocks - Nylon blocks - Change in conductance Principles underlying different methods of assessment of soil water content

17. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology DIRECT Gravimetric: evaporating water at 1050C. Thermogravimetric: Soil sample is weighted and saturated with alcohol and burned several times until a constant dry weight is obtained INDIRECT Electrical Conductance

18. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology DIRECT Gravimetric: evaporating water at 1050C. Feel Method: Thermogravimetric: Soil sample is weighted and saturated with alcohol and burned several times until a constant dry weight is obtained Advantages: ensures accurate measurements, not dependent on salinity and soil type, easy to calculate Disadvantage: destructive test, time consuming, inapplicable to automatic control, must know dry bulk density to transform data to volume moisture content, inaccurate because of soil variability There are many classifications for soil types and major differences within each classification Soil management can have a major impact upon these soil properties. Compaction is the major cause of error in bulk density. http://edis.ifas.ufl.edu/

19. رابطه آب خاك و گیاه تكميلی حاج عباسی Frequency Domain Reflectometry: radio frequency (RF) capacitance techniques Actually measures soil capacitance A pair of electrodes is inserted into the soil Soil acts as the dielectric completing a capacitance circuit, which is part of a feedback loop of a high frequency transistor oscillator Isfahan University of Technology As high frequency radio waves (about 150 MHz) are pulsed through the capacitance circuitry, a natural resonant frequency is established which is dependent on the soil capacitance, which is related to the dielectric constant by the geometry of the electric field established around the electrodes Two commercially available instruments using this technique: the Troxler Sentry 200-AP probe and the Aquaterr probe

20. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Time Domain Reflectometry (TDR): q, 28 s The soil bulk dielectric constant (K) is determined by measuring the time it takes for an electromagnetic pulse (wave) to propagate along a transmission line (L) that is surrounded by the soil Since the propagation velocity (v) is a function of K, the latter is therefore proportional to the square of the transit time (t, in seconds) down and back along the L K= (c/v)2 = ((c.t)/(2.L))2 where c is the velocity of electromagnetic waves in a vacuum (3•108 m/s or 186,282 mile/s) and L is the length embedded in the soil (in m or ft)

21. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology • TDR determinations involve measuring the propagation of electromagnetic (EM) waves or signals • Propagation constants for EM waves in soil, such as velocity and attenuation, depend on soil properties, especially q and EC The propagation of electrical signals in soil is influenced by q and EC The dielectric constant, measured by TDR, provides a good measurement of this soil water content Disadvantage: Costly, not really independent of salt content

22. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Time Domain Transmission (TDT) This method measures the one-way time for an electromagnetic pulse to propagate along a transmission line (L). Thus, it is similar to TDR, but requires an electrical connection at the beginning and ending of the length. Notwithstanding, the circuit is simple compared with TDR instruments. Disadvantages: Reduced precision, because the generated pulse is distorted during transmission; soil disturbance during installation; needs to be permanently installed in the field

23. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology NUCLEAR TECHNIQUES: Neutron Scattering, q, 1 to 2 min With this method, fast neutrons emitted from a radioactive source are thermalized or slowed down by hydrogen atoms in the soil Since most hydrogen atoms in the soil are components of water molecules, the proportion of thermalized neutrons is related to q Advantages: can measure a large soil volume, can scan at several depths to obtain a profile of moisture distribution, nondestructive, water can be measured in any phase Disadvantages: high cost of the instrument, salinity, must calibrate for different types of soils, excess tube, radiation hazard, insensitivity near the soil surface, insensitivity to small variations in moisture content at different points within a 30 to 40 cm radius, and variation in readings due to soil density variations (error rate of up to 15 percent)

24. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Gamma Attenuation: volumetric water content, < 1 min • This method assumes that the scattering and absorption of gamma rays are related to the density of matter in their path • The specific gravity of a soil remains relatively constant as the wet density changes with increases or decreases in moisture • Changes in wet density are measured by the gamma transmission technique and the moisture content is determined from this density change Advantages: can determine mean water content with depth, can be automated for automatic measurements and recording, can measure temporal changes in soil water, nondestructive measurement Disadvantages: restricted to soil thickness of 1 inch or less, but with high resolution, affected by soil bulk density changes, costly and difficult to use, large errors possible when used in highly stratified soils

25. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Soil and Water evaporation

26. LIQUID Gravimetric (Mass/Mass) Volumetric (Volume/Volume) Relative VAPOR Concentration (Mass/ volume air) Pressure (KPa) Relative Humidity WATER CONTENT

27. USES of WATER in PLANTS • 1. Constituent • 2. Solvent • 3. Reactant-product • 4. Turgidity • 5. Temperature Control

28. CONSTITUENT • Water constitutes more than 70% of fresh weight of most plants (Seeds are exception) • Between 60-90% of the water is contained in the plant cell providing both biological and physical functions. • The remaining 10-40% is contained as liquid in cell walls providing a continuum between the soil supply and the living cell.

29. SOLVENT • Dissolves both organic and inorganic constituents essential for life • Dissolves gases-CO2

30. REACTANT-PRODUCT • Photosynthesis CO2+ H2O = SUGAR • Respiration CH2O + O2 = CO2 + H2O

31. ENERGY BALANCE • Evaporation dissipates heat • Condensation-precipitation releases heat • Amount of water passing through plants as transpiration depends on environment and species Wheat 1000 kg H2O per kg dry matter Cotton 5000 kg H2O per kg lint

32. 1 mole water ~ 18 cm3 contains 6.02 x 1023 molecules 1 cm3 ~ 3.3 x 1022 (33 thousand billion billion) Consider a beach 1.6 x 106 m (1000 miles) long 200 m (656 feet) wide 100 m (328 feet) deep Volume beach = 3.2 x 1010 m3 sand Assume that each grain = a sphere 1 mm diameter With loose packing 109 (one billion) grains in 1 m3 Entire beach 3.2 x 1019 sand grains, 1000 < number of molecules in 1 cm3 water رابطه آب خاك و گیاه تكميلی حاج عباسی It would take 1000 beaches to contain as many sand grains as molecules in 1 cm3 of water Each water molecule is ~ 3 A (3 x 10-10 m) It would take 33 x 106 layers to form a layer of water 1 cm deep.

33. UNIQUE PROPERTIES of WATER + + H H 105O O -

34. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Hydrogen bond H+ O-- - H2O = + H+ Gives structural strength Bond depends on temperature: Higher is the temperature weaker is bond Positive end attraction with -ve end of other water molecules

35. رابطه آب خاك و گیاه تكميلی حاج عباسی

36. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Electro positive Hydrogen Hydrogen H-O : 0.97 A H-H : 1.54 A 1050 Oxygen Polarity angstroms Negative Symmetrical

37. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Polymer type of grouping H+ H+ O- Cations: Na+, K+, Ca2+ : become hydrated through their attraction to the Oxygen Anions or negatively charged clay surfaces: attract water through hydrogen

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39. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Some definitions Adhesion - the attraction or clinging together of unlike substances Cohesion - the attraction of a substance for itself; the mutual attraction among molecules or particles comprising a substance tat allows it to cling together as a continuous mass. absorption - the process by which one substance is taken into and included within another substance, as the absorption of water by soil or nutrients by plants. adsorption - the increased concentration of molecules or ions at a surface, including exchangeable cations and anions on soil particles. flickering clusters refers to the quasicrystalline state of water molecules while in a liquid state. The molecules associate and dissociate repeatedly in transitory or flickering polymer groups. Water molecules are attracted to one another due to the hydrogen bonding that takes place between the negatively charged end of the oxygen atom in the molecule and the positively charged ends of hydrogen atoms in adjacent water molecules.

40. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology heat of fusion (ice) The amount of energy required to turn a liquid into a solid. heat of vaporization The amount of energy required to turn a liquid to a vapour (to overcome the attractive forces between adjacent molecules in a liquid). dipole moment a measure of the tendency of a polar molecule to be affected by an electrical or magnetic field (i.e., NMR - Nuclear magnetic resonance) Volumetric heat capacity is the change in the heat content of a unit volume per unit change in temperature. Specific heat is the change in the heat content of a unit mass per unit change in temperature. surface tension A molecule at the surface of a liquid is not completely surrounded by other molecules of the liquid. The forces acting upon it are unbalanced, with the result that it experiences a stronger attraction into the body of the liquid (cohesion) rather than into the less dense gaseous phase. This unbalanced force draws the surface molecules inward with and results in the tendency for the surface to contract and the molecules to be slightly denser at the surface.

41. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology sublimation the direct transition from the solid state to the vapor state hydrophobic water repellent capillary attraction - a liquid's movement over or retention by a solid surface due to the interaction of adhesive and cohesive forces. capillary fringe a zone just above the water table that is maintained in an essentially saturated state by capillary forces of lift. viscosity (centipose, cP, N s m-2 x 10-3, kg m-1 s-1). When a fluid is moved in shear (that is to say, when adjacent layers are fluid are made to slide over each other), the force required is proportional to the velocity of shear. Viscosity is the proportionality factor. It is the property of the fluid to resist the rate of shearing and can be visualized as an internal friction. Fluids of lower viscosity flow more readily. Thus oil has a higher viscosity than water. Fluidity is the reciprocal of viscosity. Viscosity is the preferred term.

42. رابطه آب خاك و گیاه تكميلی حاج عباسی Cohesive – forces of attraction between like molecules. At an air-water interface– surface tension. Adhesion – attraction of one substance for a substance of another kind. Tensile strength – work that must be done to create or extend a new or larger surface. Viscosity – resistance to flow.

43. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology If water were an ordinary compound whose molecules are subject to weak forces, its boiling and freezing point would fall below hydrogen sulfide Strong hydrogen bonding between water molecules prevents this Water occurs in all three states (solid, liquid, and gaseous) at prevailing temperatures on the earth’s surface Example: Ice cubes in a glass at room temperature

44. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Why water wets clean glass? • Surface of glass has O and unpaired electrons • Water molecules form hydrogen bond • Force stronger than gravity Why water does not stick to glass surface coated with grease? • Surface of grease has no O and free electrons • Water molecules cannot form hydrogen bond • Therefore, water do not stick

45. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Forces acting on a water molecules Air-water Interface Air At point A: Attraction of air for water molecules is much less than that of water molecules for each other. A B At point B: Forces acting on water molecule are equal in all direction Water Consequently, there is a net downward force on the surface molecules, and result is something like a compressed film at the surface. This phenomenon is called surface tension

46. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Surface Tension The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface "film" which makes it more difficult to move an object through the surface than to move it when it is completely submersed. • Surface tension is typically measured in dynes/cm. The force in dynes required to break a film of length 1 cm • Equivalently, it can be stated as surface energy in ergs/cm2 • Water at 20°C has a surface tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and 465 for mercury

47. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Contact Angle • Solid • Liquid • Gas Liquid and gas (air) in contact with solid Interface between air and water forms a definite angle “contact angle” Young’s equation L Air gsa > gsw; cos a = + or a < 900 Angle of contact is acute in a liquid that wets the solid Solid L Air Angle of contact is obtuse (between 90 and 180) in a liquid that does not wet the solid Solid

48. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Hydrophilic Versus Hydrophobic Soils When the adhesive forces between water molecules and an object are weaker than the cohesive forces between water molecules, the surface repels water and is said to be hydrophobic. Hydrophobic soils restrict the entry of water, which 'balls up' or sits on the soil in beads rather than infiltrating the soil. Hydrophobic soils exhibit an obtuse (greater than or equal to 90o) wetting angle that causes capillary repulsion, so preventing water from entering soil pores Hydrophilic or normally wettable soils display an acute (less than 90o) angle of contact with water, allowing infiltration. adhesive forces between water molecules and an object are stronger than the cohesive forces between water molecules

49. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology Capillary Fundamentals and Soil Water Cohesion: Attraction of molecules for each other Adhesion: Attraction of water molecules for solid surfaces By adhesion, solids hold water molecules rigidly at their soil-water surface By cohesion water molecules hold each other away from solid surfaces Gravity Together it is possible for soil solids to retain water and control it’s movement Capillary

50. رابطه آب خاك و گیاه تكميلی حاج عباسی Isfahan University of Technology The dipolar interaction between water molecules represents a large amount of internal energy (the energy associated with the random, disordered motion of molecules) and is a factor in water's large specific heat (the amount of heat per unit mass required to raise the temperature by one degree Celsius). The dipole moment of water provides a "handle" for interaction with microwave electric fields in a microwave oven. Microwaves can add energy to the water molecules, whereas molecules with no dipole moment would be unaffected. Dipolar Bonding in Water