Module 4 - Soil Physical Properties and Soil Water.pdf

56 Module 4: Soil Physical Properties and Soil Water Module Overview This module provides a background on the different soil physical properties, their nature, behavior, and importance to the agricultural and environmental functio...

56 Module 4: Soil Physical Properties and Soil Water Module Overview This module provides a background on the different soil physical properties, their nature, behavior, and importance to the agricultural and environmental functions of the soil. How these properties affect and are affected by management practices are also included in this module. Studying the physical properties of the soil gives us ideas on its uses, potentials, threats and possible measures to conserve it. Motivation Question In what way humans can affect soil physical properties? Module Pretest Instruction: (Please encircle the letter of your choice.) 1. These are soil properties that are readily changed on short time scales under natural conditions. a. Static properties b. Dynamic properties c. Chemical properties 2. Below are examples of soil physical properties, except: a. Soil pH b. Soil color c. Soil structure 3. A soil physical property is used as an index of soil compaction. a. Soil texture b. Bulk density c. Particle density 4. The finer the particle, the higher its specific surface area: a. True b. False 5. A soil with high porosity means: a. It limits root penetration. b. It can accommodate a large volume of air and water. c. It has a high bulk density 6. At field capacity, water in the soil is held at a tension of: a. 0.3 bar b. 15 bars c. 30 bars 7. A soil with high hydraulic conductivity means: a. Water moves slowly b. Water moves quickly c. The soil is saturated Page 56 of Vision: A globally competitive university for science, technology, and environmental conservation. 152 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. DSS-IM-01  57 8. Expression of water content wherein all pores are filled with water. a. Field capacity b. Permanent wilting point c. Saturation 9. Organic matter addition promotes aggregate stability. b. a. True b. False 10. This refers to the entry of water through the soil surface. a. Infiltration b. Run-off c. Permeability Page 57 of Vision: A globally competitive university for science, technology, and environmental conservation. 152 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. DSS-IM-01  58 Lesson 4.1: Soil Physical Properties: Types, Definition and Determination Lesson Summary This lesson discusses the types, definitions, and determination of the most commonly determined soil physical properties such as soil color, soil texture, soil structure, soil density and porosity, and soil consistency. The lesson includes discussions on the effects of soil management on these soil properties. Learning Outcomes At the end of the lesson, the students will be able to: 1. Develop an understanding of the different soil physical properties, 2. Know the relationship between soil physical properties and other soil properties, and 3. Know some practices on how to manage these properties properly Motivation Questions 1. As a student, have you ever wondered why a farmer plows his field before planting? 2. Who do you think is the most significant contributor to soil compaction? Discussion Soil physical properties reflect the composition, size and arrangement of the solid particles. The most commonly measured are soil color, soil texture, soil structure, soil density and porosity, and soil consistence. Types of Soil Physical Properties 1. Static Soil Physical Properties These are the properties that do not change on short time scales under natural conditions or without significant applied force. 2. Dynamic Soil Physical Properties Page 58 of Vision: A globally competitive university for science, technology, and environmental conservation. 152 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. DSS-IM-01  59 These are the properties that are readily changed on short time scales under natural conditions or with relatively minor amounts of force. SOIL COLOR It is the most prominent and easily determined soil physical property. It has a little direct effect on the soil but is an indicator of some soil properties. There are many things we can tell about the soil by observing the color. Organic matter content -- the higher the organic content, the darker the soil color Soil color and soil temperature -- dark-colored soils absorb more heat, so they warm up quicker and have higher soil temperatures. Soil color and parent material -- generally dark parent material will develop into dark soils. Soil color and drainage -- soil drainage refers to the length of time soil is waterlogged and not how fast the soil is drained. Poorly drained soils are generally gray in color. Figure 10. A well-drained and highly weathered soil from Silago, Southern Leyte showing deep red color due to iron oxides (Photo by V.B. Asio) Relationship of Soil Color to Drainage Soil color is essential in determining a soil's drainage and depth to the water table. It can be vital in predicting land use hazards. Soil Drainage: refers to the length and duration of saturation and is not a measure of how fast water drains from the soil. Soil Drainage Class: 1. Well-drained - no gray colors with the top 100 cm. 2. Moderately well-drained - gray colors between 50 to 100 cm from the surface 3. Somewhat poorly drained - gray colors between 25 to 50 cm from the surface 4. Poorly drained - gray colors within 25 cm from the surface 5. Very Poorly drained – gray colors within 25 cm from the surface and has an O horizon Page 59 of Vision: A globally competitive university for science, technology, and environmental conservation. 152 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. DSS-IM-01  60 Figure 11. A young and poorly drained lowland soil in Hilongos, Leyte showing gray color and brown mottles due to poor drainage (Photo by V.B. Asio) Mottles or mottling – are spots or blotches. They indicate that the soil has been subject to alternate wetting (reducing) and dry (oxidizing) conditions. Soil Color Determination Munsell Color System: A standard system used by soil scientists and geologists. The system has the following color parameters: 1. Hue: dominant spectral color 2. Value: lightness - darkness; white to black 3. Chroma: color purity or intensity Color Notation: 10YR 5/2 10YR – the Hue 5 – the Value 2 – the chroma Use the Munsell Color Chart. A soil is considered gray if it has a CHROMA OF 2 OR LESS Additional Things to Take Note: red, yellow, and light brown colors – likely due to Fe oxides dark brown or black colors – likely due to organic matter or Mn oxides low color value = high organic matter content high chroma = well-drained soil, oxidizing conditions chroma of 2 or less = red Fe-oxide coatings had been removed under reducing conditions Page 60 of Vision: A globally competitive university for science, technology, and environmental conservation. 152 Mission: Development of a highly competitive human resource, cutting-edge scientific knowledge TP-IMD-02 and innovative technologies for sustainable communities and environment. V0 07-15-2020 No. DSS-IM-01  61 SOIL TEXTURE Soil texture is a stable soil property, which means it is not affected by soil and crop production practices. It is defined as the relative proportion of sand, silt, and clay. Together, these three soil separates must add up to be 100%. The organic matter is not a part of the soil's texture. Each soil separate represents a distinct physical size group of mineral particles. We will be using these separates the rest of the semester. As already discussed in Module 3, the effective diameter (according to the ISSS classification) of the soil particles, also called soil separates, is as follows: Sand 2.0 - 0.02 mm Silt 0.02 - 0.002 mm Clay