1 / 43

Tonight

Tonight. Review mineralogy and soil colloids Soil Reaction Soil Water Assignment 3 due Assignment 4 and Water calculations handed out. Soil Reaction. Soil reaction is the degree of acidity or alkalinity of a soil, usually expressed as a pH value. Soil pH = -log [H + ]

sokanon
Download Presentation

Tonight

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tonight • Review mineralogy and soil colloids • Soil Reaction • Soil Water • Assignment 3 due • Assignment 4 and Water calculations handed out

  2. Soil Reaction • Soil reaction is the degree of acidity or alkalinity of a soil, usually expressed as a pH value. • Soil pH = -log [H+] • Soil pH is an indicator of physical, chemical and biological properties in soil. • Soil pH is also related to the cations present on the exchange complex.

  3. pH of Common Materials • Milk of magnesia: ~10.5 • Bicarbonate of soda: ~8.3 • Pure water: 7.0 • Milk: ~6.8 • Natural rain: 5 to 6 • Beer/coffee: ~4 • Lemon Juice: ~2

  4. Fig. 7.2. Descriptive terms for Soil pH ranges

  5. Dark Gray Luvisol Orthic Humo-Ferric Podzol Orthic Black Chernozem Fig. 7.1. Soil have distinct properties Credit: Pedosphere.com

  6. Soil pH vs Soil Type & Depth • Let us study data in Table 7.2 (Section 7.3)

  7. Soil pH vs Cation Composition • Total cation exchange capacity (TCEC) is a function of quantity of clays, organic matter and iron and aluminum oxides (Section 6) • Types of clay are very important! (Section 6)

  8. Soil pH vs Cation Composition • Base cations (Ca++, Mg++, K+, Na+) concentration decreases as soil becomes more acidic (pH decreases) • Let us study data in Table 7.3 (Section 7.3)

  9. Percent Base Saturation • Basic cations: Ca++, Mg++, Na+, K+ • Acidic cations: Al+++, H+ • Percent base saturation: A measure of the proportion of basic cations occupying the exchange sites of a soil

  10. Formula • Cation exchange capacity is the sum of all cations on the exchange complex • % Base saturation =  (Ca++, Mg++, K+, Na+) x 100 Cation Exchange Capacity

  11. pH of Diagnostic Horizons • Let us studyTable 7.4

  12. Fig. 6.9. Impact of soil pH on net charge ofnoncrystalline aluminum oxide. At low pH, H ions become bound to Al and Fe oxides Credit: Pedosphere.com

  13. Fig. 7.3. Soil pH vs cations on the exchange complex (Brady and Weil, 1996)

  14. Dissolution of amorphous Al(OH)3 • Al(OH)3 + H+ Al(OH)2++ H2O • Al(OH)2++ H+ Al(OH)+++ H2O • Al(OH)+++ H+ Al++++ H2O • The equilibrium reactions result in buffering of soil

  15. Buffering Mechanisms (Table 7.6) • Oxidation of pyrite and reduced S minerals; dissolution of minerals: pH 2 to 4 • Aluminum compounds: pH 4.0 to 5.5 • Cation exchange: pH 5.5 to 6.8 • Organic matter and minerals: pH 6.8 to 7.2 • Ca and Mg carbonates: pH 7.2 to 8.5 • Exchangeable Na+; Dissolution of solid sodium carbonate: pH 8.5 to 10.5

  16. Soil Acidity Types • Active acidity: The activity of hydrogen ions in solution • Reserve acidity: The acidity that is associated with the exchange complex. It is neutralized by lime or other alkaline material

  17. Classification of Soil Acidity - + - + + - - + + + - - + - + + - Clay surface + - + Bulk solution + + - - + + - + + - + - - + - Fig. 7.4. Hydrogen is part of the crystal lattice,and can be present as an exchangeable cation and in the soil bulk solution

  18. Nutrient Availability • The availability of nutrients is strongly related to its solubility at different pH values • At extreme pH values, solubility of some nutrients increases tremendously, leading to toxicity of plants • Let us study Fig. 7.5 in Section 7.7

  19. Acidification Use of ammonium-based fertilizers (NH4)SO4 + 4O22HNO3 + H2SO4 + 2H2O Acid Deposition Nitric (HNO3) + Sulfuric (H2SO4) acids

  20. Acidification • Drainage of some coastal wetlands leads to the oxidation of pyrite (FeS2), iron sulfide (FeS) and elemental S and formation of sulfuric acid

  21. Micelle Micelle Liming soils Use liming materials: CaCO3; Ca(OH)2,CaO; MgCO3 -H+ + CaCO3 = -Ca2+ +H2O and CO2 Are CaCl2 or CaSO4 liming materials?If yes, why? If not, why not?

  22. Lecture Material • Motivation • Classification of soil water • Soil water potential curves • Water movement • Water properties and texture triangle

  23. 16 r Particle size & pore space Large Particle 2 x 2 x 2 = 8 Pore radius = 4r

  24. 16 r Particle size & pore space Medium Particle 4 x 4 x 4 = 64 Pore radius = 2r

  25. 16 r Particle size & pore space Small Particle Pore 8 x 8 x 8 = 512 radius = r

  26. Fig. 1.9. Pores and particles in soil (Pawluk) Credit: Pedosphere.com

  27. Fig. 3.3. Soil textural classes in the Canadian System of Soil Classification Credit: CSSC & Pedosphere.com

  28. Fig. 8.10. Saturated and Unsaturated Flow

  29. Fig. 8.4. Capillary rise and capillary retention Credit: Brady & Weil, 1996; Kohnke, 1968

  30. Fig. 8.6. Interaction of water molecules with clay surfaces, and cations and anions in soil Credit: Pedosphere.com

  31. Fig. 8.5. Classification of soil water (after Heaney, Crown and Palylyk, 1995). Credit: Pedosphere.com

  32. Matric Potential • Matric Potential: Adhesion of water to surfaces through adsorption and capillarity; markedly reduces the energy state of adsorbed water molecules • Matric potential is universally important and is used in calculations of water movement

  33. Osmotic Potential • Osmotic Potential: Attraction of ions and other solutes for water reduces the energy level of water molecules • Osmotic potential is attributable to the presence of solutes in the soil solution.

  34. Gravitational Potential • Yg = ghwhere g is the acceleration due to gravity and h is the height of soil water above a reference elevation. • Gravity plays an important role of removing excess water from the upper rooting zones following heavy precipitation or irrigation.

  35. Soil Water Potential • The difference in energy levels between pure water and soil water is termed soil water potential • Difference in energy level determines the direction and rate of water movement in soils and plants

  36. Soil Water Potential • Soil water potential is made up of matric, osmotic and gravitational potentials • Water flows from a point which has a higher water potential to another point which has a lower soil water potential

  37. Fig. 8.5. Classification of soil water (after Heaney, Crown and Palylyk, 1995). Credit: Pedosphere.com

  38. Fig. 8.7. Soil water potential curves Credit: Pedosphere.com

  39. Water Movement • Saturated flow: Vertical movement of water due to force of gravity in a soil in which all the pores are completely filled with water. • Movement can be defined by Darcy’s equation

  40. Fig. 8.8. Darcy’s equation (q = Ks * DH/DL) Credit: Pedosphere.com

  41. Table 8.2. Hydraulic conductivity in soils with different textures Credit: After Hanks and Ashcroft, 1980

  42. Fig. 8.9. Unsaturated Flow

More Related