Soil Physical Properties • Color • Texture • Density (particle density vs. bulk density) • Pore space (porosity) • Structure • Aggregate stability
Physical properties are important 1) Control plant growth through influence on: Soil temperature (darker = warmer) Soil aeration (sandy soils well aerated) Soil moisture content (clayey soils stay wet) 2) Indicate important characteristics of a soil • e.g., lots vs. little organic matter
Objectives • Know what color tells you about a soil • Describe the concept of soil texture and its importance • Use the textural triangle to determine a soil’s textural class based on its sand, silt and clay content
Physical properties – Color • covaries with • O.M. • Fe and Al oxides • moisture saturation • mineralogy (e.g., calcite, hematite=Fe2O3) • Color
Color “quantified” using the Munsell system • Hue (e.g., 10YR) tells you general shade (red, yellow); DOES NOT tell you how dark the soil is • Value (e.g., 10YR 5/6) tells you how dark the soil is: 0 is darkest • Chroma (e.g., 10YR 5/6) tells you brightness (0 = gray). Indicates moisture conditions (bright = dry)
10R 10YR 10R 10P 10Y 10Y 10B 10G Soil Color: Hue 2.5 YR 5YR 7.5 YR 2.5 Y 5 Y 7.5 Y Go clockwise to numerically add next color!
10YR page of Munsell color book (also see Fig 4.1 of your text)
Example Question • Which soil horizon likely has more organic matter, one that is classified as 5R 5/6, or one that you decide is 10YR 1/7?