Delineating Soil Horizons Soil as a Natural Body

Delineating Soil Horizons

Soil as a Natural Body Differentiation Additions Losses Parent Material Translocations Transformations Bedrock

Soil Horizons Roughly parallel layers in the soil with varying composition and properties

Master Horizons

Criteria for Characterizing Soil Horizons Color Texture Density Structure Organic matter Mineralogy Chemistry

Soil Color

Soil Color Determinants • • • Mineralogy of the soil/parent material Relative amount of organic matter Hydrology of the soil Soil chemistry Soil Microbes

Coloring Agents in Soils Organic Matter Grey to Black coloration particularly in topsoil or A horizon material. Can be found in the sub-soil as an accumulation Elements and Compounds Iron, manganese Reddish to yellow-brown Purplish black

Soil Color Determination

Munsell Soil Color Hue Value related to total amount of light reflected. dominant spectral color; related to the wavelength of light. Related to the proportions of red to yellow. In soils we only use 1/5 of the color chips available. Chroma measure of the strength of spectral color

10 R 0 2. 5 YR 7. 5 YR 10 YR 0 2. 5 Y 5 Y

Hue Pages 10 R Red 2. 5 YR 7. 5 YR 10 YR 2. 5 Y 5 Y Yellow Increasingly dominated by yellow spectral color Florida soils dominated by 7. 5 YR and 10 YR pages

Soil Color

Hue = 10 YR Value = 6 Chroma = 3 Munsell Color 10 YR 6/3

10 YR 2/1 10 YR 5/6

Pink Pale Red Weak Red light Red Dark Red

Summary A horizon – mid/low value - low chroma E horizon – high value - low chroma B horizon – ? value - ? chroma

Water table depth Oxygen status Development decisions

Hydric Soil Classification Hue 10 YR or Yellower Value ≤ 3 Chroma ≤ 1 “Black Histic”

Mineral Formula Size Munsell Color goethite Fe. OOH (1 -2 m m) 10 YR 8/6 yellow goethite Fe. OOH (~0. 2 m m) 7. 5 YR 5/6 strong brown hematite Fe 2 O 3 (~0. 4 m m) 5 R 3/6 red hematite Fe 2 O 3 (~0. 1 m m) 10 R 4/8 red lepidocrocite Fe. OOH (~0. 5 m m) 5 YR 6/8 reddish-yellow lepidocrocite Fe. OOH (~0. 1 m m) 2. 5 YR 4/6 red ferrihydrite Fe (OH)3 2. 5 YR 3/6 dark red glauconite K(Six. Al 4 x)(Al, Fe, Mg)O 10(OH)2 5 Y 5/1 dark gray iron sulfide Fe. S 10 YR 2/1 black pyrite Fe. S 2 10 YR 2/1 black (metallic) jarosite K Fe 3 (OH)6 (SO 4)2 5 Y 6/4 pale yellow todorokite Mn. O 4 10 YR 2/1 black humus 10 YR 2/1 black calcite Ca. CO 3 10 YR 8/1 white dolomite Ca. Mg (CO 3)2 10 YR 8/2 white gypsum Ca. SO 4× 2 H 2 O 10 YR 8/3 very pale brown quartz Si. O 2 10 YR 6/1 light gray

Low Value High Value high Chroma Low Chroma

Criteria for Characterizing Horizons Color Texture Density Structure Organic matter Mineralogy Chemistry

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