Introduction to Soil Descriptions. Part 2 of 3

Transcription

1 Introduction to Soil Descriptions Part 2 of 3 1

2 Acknowledgement This work was supported [in part] by the National Decentralized Water Resources Capacity Development Project with funding provided by the U.S. Environmental Protection Agency through a Cooperative Agreement (EPA No. CR ) with Washington University in St. Louis. The results have not been reviewed by EPA or Washington University in St. Louis. The views expressed in this presentation are solely those of NCSU, and University of Arkansas and EPA and Washington University in St. Louis do not endorse any products or commercial services mentioned in the presentation. 2

3 Soil Consistence Rule.1941 (a3) 3

4 Definition of Consistence Consistence is the degree and kind of cohesion and adhesion that soil exhibits, and/or the resistance of soil to deformation or rupture under an applied stress. 4

5 Consistence Rupture Resistance Stickiness Plasticity Manner of Failure Penetration Resistance Consistence is the degree and kind of cohesion and adherence that soil exhibits, and/or the resistance of soil to deformation or rupture under applied stress. Moisture content strongly influences soil s consistence. There are 5 ways to record consistence in the field; Rupture Resistance, Manner of Failure, Stickiness, Plasticity, and Penetration Resistance. Each type is recorded at specific moisture contents or within given moisture content ranges. 5

6 The Field Book for Describing and Sampling Soils Consistence Moist consistence Wet consistence Soil Taxonomy has changed since the last rule rewrite. Wet Consistence: Historically, moderately sticky was called sticky. Historically, moderately plastic was called plastic. So technically the regulations have not kept up with the changes in soil taxonomy. Also, Soil Taxonomy is not the reference we use since The Field Book for Describing and Sampling Soils was published 6

7 Moist Consistence Moist Consistence provides a measure of the tendency for peds or masses of soil material to break when pressure is applied between the thumb and forefinger. Categories: loose, very friable, friable, firm, very firm, or extremely firm Loose: Non-coherent. Very friable: Soil material crushes under very gentle pressure but coheres when pressed together. Friable: Soil material crushes easily under gentle to moderate pressure between thumb and forefinger, and coheres when pressed together. Firm: Soil material crushes under moderate pressure between thumb and forefinger but resistance is distinctly noticeable. Very Firm: Soil material crushes under strong pressure; barely crushable between thumb and forefinger. Extremely Firm: Soil material crushes only under very strong pressure; cannot be crushed between thumb and forefinger and must be broken apart bit by bit. 7

8 Rupture Resistance Classes: Blocks, Peds, and Clods Dry Moist Cementation Description Loose Loose n.a. Cannot get samp. Soft V. Friable Non-cem Very slight FF Sl. Hard Friable Ex. w. cem Slight FF Mod. Hard Firm V. w. cem Moderate FF Hard V. Firm W. cem Str. FF V. Hard Ex. Firm Mod. cem Moderate HF Ex. Hard Sl. Rigid Str. cem Foot pressure Rigid Rigid V. Str. cem Light Blows V. Rigid V. Rigid Indurated Strong Blows The Field Book for Describing and Sampling Soils describes the specific force that corresponds with each class. A 2.5 to 3.1 cm cube should be used or a plate cm long by 0.5 cm thick. 8

9 FRIABLE Slight FF (Finger Force) Fails under slight force applied slowly between thumb and forefinger i.e. very rich cake or biscuits 9

10 FIRM Moderate FF (Finger Force) Fails under moderate force applied slowly between thumb and forefinger i.e. well done, dry toast Skin on fingers is depressed while pressure is applied Tendons of fingers will barely flex 10

11 VERY FIRM Strong FF (Finger Force) Fails under strong force applied slowly between thumb and forefinger i.e. very stale bread, biscotti Skin on fingers is depressed to bone, may almost be painful Tendons of finger will flex 11

12 Wet Consistence Wet consistence measures the stickiness or plasticity of wet soil material. Stickiness - The capacity of soil to adhere to other objects. Plasticity - The degree to which puddled or reworked soil can be permanently deformed without rupturing. Use criteria set forth in The Field Book for Describing and Sampling Soils. Stickiness and plasticity are estimated at the moisture content that displays the greatest adherence and maximum plasticity. See page

13 Stickiness The capacity of soil to adhere to other objects Estimated at moisture content that displays maximum adherence between thumb and fore finger The capacity of soil to adhere to other objects such as your fingers. Estimated at moisture content that displays maximum adherence between thumb and fore finger. 13

14 Stickiness Classes Non-Sticky little or no soil adheres to fingers after release of pressure Slightly Sticky soil adheres to both fingers after release of pressure with little stretching on separation of fingers Moderately Sticky soil adheres to both fingers after release of pressure with some stretching on separation of fingers Very Sticky - soil adheres firmly to both fingers after release of pressure with stretches greatly on separation of fingers 14

15 Non-Sticky 15

16 Moderately Sticky 16

17 Very Sticky 17

18 Plasticity Class Non-Plastic will not form a 6 mm dia, 4 cm long wire, or if formed, can not support itself if held on end Slightly Plastic 6 mm dia, 4 cm long wire wire supports itself, 4 mm dia, 4 cm long wire wire does not Moderately Plastic 4 mm dia, 4 cm long wire wire supports itself, 2 mm dia, 4 cm long wire wire does not Very Plastic 2 mm dia, 4 cm long wire wire supports itself Plasticity classes; Non-Plastic will not form a 6 mm wire, or if formed, can not support itself if held on end Slightly Plastic 6 mm wire supports itself, 4 mm wire does not Moderately Plastic 4 mm wire supports itself, 2 mm wire does not Very Plastic 2 mm wire supports itself 18

19 Moderately Plastic 19

20 Very Plastic 4 cm long 2 mm diameter 20

21 Inferences Clayey textures (clay, silty clay, sandy clay, some clay loam and silty clay loams) with very firm moist consistence and very sticky, very plastic wet consistence are likely to contain 2:1 shrink-swell clay Clayey textures that are friable with only moderately sticky and plastic wet consistence contain less amounts of active shrink-swell clay or are kaolinitc 21

22 Estimating Clay Mineralogy from Consistence and Color Wet Consistence Moist Consistence Moist Color Mineralogy Very Sticky Very Plastic Firm to Very Firm 10YR 2.5Y 5Y 2:1 Smectite Slightly to Moderately Sticky Slightly to Moderately Plastic Friable to Firm 2.5YR or Redder (10R, 7.5R) 1:1 Kaolinite Moderately Sticky Moderately Plastic Firm 5YR 7.5YR 10YR Mixed, 1:1 and 2:1 22

23 Soil Color Rule

24 Coloring agents in the soil Organic matter darkens the soil. Iron (Fe) is the primary coloring agent in the subsoil. Manganese (Mn) is also common in some soils. What causes the colors we see in the soil. Organic matter darkens the soil and is typically associated with surface layers. Organic matter will mask all other coloring agents. Iron (Fe) is the primary coloring agent in the subsoil. The orange brown colors associated with well drained soils are the result of Fe oxide stains coating individual particles. Manganese (Mn) is common in some soils resulting in a very dark black or purplish black color. 24

25 Why do we care about soil color? It is the most obvious and easily determined soil characteristic. Important characteristics can be inferred from soil color. Well drained (aerobic) soils have uniform bright colors. Soils with a seasonal saturation are mottled. Wet soil have more gray colors Color helps us determine the treatment capacity of the soil 25

26 Coating of Fe 2 O 3 (rust) Color changes Remove Fe Brown Soil Gray Soil Adapted from Mike Vepraskas 26

27 Munsell Color System Hue refers to the dominant wavelength of light (red, yellow, green, etc.). Value refers to the lightness and darkness of a color in relation to a neutral gray scale. Chroma is the relative purity or strength of the Hue. Notation Hue Value/Chroma 10YR 5/6 Putting all this together the Munsell Color System was created. It was initially designed for manufacturing but soon made its way into any field that needed to record and communicate color. Hue refers to the dominant wavelength of light (red, yellow, green, etc.). Value refers to the lightness and darkness of a color in relation to a neutral gray scale. Chroma is the relative purity or strength of the Hue. Notation: Hue Value/Chroma 10YR 5/6. 27

28 Munsell Soil Color Chart 28

29 What s most important? Chroma is most important to describe correctly. Chromas of 2 or less 29

30 Color Patterns Matrix color is the dominant color in the soil. Mottling is spots or blotches of color in the soil that differ from the matrix color. Redoximorphic features are mottles that relate to the aeration or drainage of the soil. In describing colors it is important to determine the variation in color throughout the soil. Matrix color is the dominant color in the soil. Mottling is spots or blotches of color in the soil that differ from the matrix color. The pattern may relate to the aeration or drainage of the soil. Gley colors are low chroma matrix colors with or without mottles. If the soil has a gley color it is likely to be reduced and wet for much of the year. 30

31 By Rule.1942, soil color tells me the water table is here 31

32 <2% - few 2-20% - common >20% - many Percent Likewise the percent of the given feature should be recorded. Although NRCS does use this chart to indicate abundance it is better to record the actual percent using the charts in the Munsell book to estimate. 32

33 Percent figure seen in the Munsell Book. Note the each square can be subdivided in to quarters. There is the same amount of black in each quarter. This helps in determining % when the features are of different size. 33

34 Each 1/4 th of any one square has the same amount of black Each 1/4 th of any one square has the same amount of black, thus features of differing size can be estimated. 34

35 NC STATE UNIVERSITY DEPARTMENT of SOIL SCIENCE 35

36 6.25% 1.5% 25% NC STATE UNIVERSITY DEPARTMENT of SOIL SCIENCE 36

37 Recording Soil Colors Soil should be moist...this is the most common way soil colors are recorded. Always use sunlight. Do not use artificial light. Do not wear sunglasses or tinted glasses. Always use a freshly exposed face or ped. Do not crush or rub the soil before getting a color. Determine the matrix and all subordinate colors (mottles). Colors should be recorded in a specific fashion. Soil should be moist...this is the most common way soil colors are recorded. Always use direct sunlight. Do not use artificial light. Do not wear sunglasses or tinted glasses. Always use a freshly exposed face or ped. Do not crush or rub the soil before getting a color. Determine the matrix and all subordinate colors (mottles). 37

38 Summary Internal drainage can be related to consistence Mineralogy is inferred from consistence Color is used to determine soil wetness Some inferences to soil mineralogy can also be made from consistence combined with color (Hue) 38