Evaluating Physical Data Objectives: you should be able to:

• Locate the physical data on the data sheet• Describe common physical data methods• Give examples of how to apply physical data• Determine if the physical data is internally

consistent• Calculate fundamental relationships

Exercise - find physical data Complete exercise SSL information manual (SSIR 45) pp

204-206

Exercise - find physical data Find and write the following (page 204):

• Soil Survey Number ______ • Percent clay for C3 horizon _______• Percent fine silt for BS horizon ______• 1/3 bar bulk density for Ap2 horizon ______ • 15 bar on moist soil for Ap1 horizon ______• Water dispersible clay for Ap1 horizon _____• Which horizons have 15bar/clay greater than

0.6? ______• What is the method code for WRD? _____

Exercise - find physical data Find and write the following (page 204):

• Soil Survey Number - S88ME-003-001• Percent clay for C3 horizon - 23.2• Percent fine silt for BS horizon - 28.9 • 1/3 bar bulk density for Ap2 horizon - 1.24 • 15 bar on moist soil for Ap1 horizon - 9.9• Water dispersible clay for Ap1 horizon - 7.7• Which horizons have 15bar/clay greater

than 0.6? Ap1, Ap2, BS, C1 • What is the method code for WRD? 4C1

Physical Methods Each data element has a method

Each method has a method code

The method is • the standard operating procedure• part of the quality assurance program

Lab methods are in SSIR 42: Laboratory Methods Manual

SSIR 42 was written for laboratory technicians

SSIR 51 – Field and Laboratory Methods

Internal Consistency Consistency of data – does it follow

expected trends

-with other analyses

-within pedons

-with genetically and geographically associated pedons

Laboratory consistency (repeatability) is monitored by use of standard samples for each batch.

Evaluating the consistency of physical data

Maximum, minimum, and representative values

Depth trends within a pedon : clay, Db …

Trends in physical, chemical and mineralogical data are compared.

Compare apples to apples. Know the methods used for the data you are comparing. Use the appropriate method.

Inconsistency?

Rerun lab data? Representative site? Variability at sampling site? Sampling procedure.

Reevaluate your hypothesis

Physical Analytical Methods

Particle-Size Bulk Density Water Retention COLE Aggregate Stability

NASIS ‘Super 7’

Coarse fragments Sand Silt Clay OM Bulk density Ksat

Particle-size analysis

Method 3A1 describes measuring sand, silt, and clay fractions with the pipette and sieves.

The sedimentation theory is based on Stokes’ Law.

Most applicable for soils with crystalline clays.

Particle-size analysis (pipette)

The method is precise within 1.5 percent, absolute.

Only method to obtain fine clay and CO3 clay.

Method is time consuming and labor intensive.

Pipette PSDA analysis Errors with pipette analysis are associated

with sampling and measuring.

Uses pretreatments: OM, salts CO3 …

Generally considered to be superior to other sedimentation methods, particularly at low clay contents where the hydrometer has low sensitivity.

Hydrometer PSDA analysis Less equipment, quicker

Commonly does not remove OM and salts.• (Dispersion can be a problem.)

The major source of error is in the hydrometer reading. (Gee and Bauder, 1979) An error of +- 1 g/L in the hydrometer reading results in an error of about +- 2 wt % for clay size particles.

Evaluation and Interpretation of PSDA Data Lab vs. field texture

Clay distribution with depth and morphology; (argillic? ).

Clay illuviation - fine clay distribution (Higher ratio of fine clay to total clay than overlying and underlying horizons.)

Distribution of silt and sand fractions (PM discontinuities)

Weighted average for control section79CA093001 Tangle

control section: 15-65 cm

Hrz Top Bot Thick Clay Product

A1 0 2 12.6

A2 2 15 12.6

Bt1 15 40 25 16.6 415

Bt2 40 71 25 47.1 1178

Bt2 71 109 35.2

Bt3 109 145 31.6

Clay Weighted Average 31.9 (sum/50)

Examples of Data Interpretation

• Typical calculations - PSD– Weighted average for control section

• SSIR 45 pp. 16-17

– PSA on clay-free basis• SSIR 45 pp. 188-199

– Changing basis• whole soil• <75 mm• with soil organic carbon

PSA on clay-free basis

clay fsilt csilt vfs fs ms cs vcs

A1 12.6 15.2 17.5 17.2 7.5 7.7 10 12.3

Divide by 100-clay 17.4 20.6 20.8 9.1 8.3 10.8 13.7

Use to determine PM, lithologic discontinuities

Changing BasisSieve no 4 10 40 200 (1) Whole soilPercent 10 20 15 5 15 15 20Size(mm) 250 75 5 2 0.42 0.074

Sieve no 4 10 40 200 (2) < 75 mmPercent 21.4 7 21.4 21.4 28.7 Divide <75 mm by 1->75/100

Size(mm) 75 5 2 0.42 0.074

10 40 200 (3) < 2mm

29.9 29.9 40.1 Divide each fraction (2) by2 0.42 0.074 1->2mm/100)

sand silt clay Textural separates by

25 39 36 particle size analysis2 0.05 0.002

om sand silt clay Add OM removed during

15 21 33 31 particle size analysis2 0.05 0.002 fraction * 1 - OM/100

PSDA – comparison of standard vs. ‘gypsic’ method

SAMPLE HORIZON GYP %SAND %,

STD METH.

SAND %, GYPSIC METH.

SILT %, STD METH.

SILT %, GYPSIC METH.

CLAY %, STD METH.

CALC. CLAY %, GYPSIC

METH.

Series: Loki; Coarse-loamy, gypsic, thermic Typic Calcigypsid

06N04753 A0 20 24 51 48 29 28

06N04754 Bw0 14 18 49 46 37 36

06N04755 Bk3 8 15 46 44 45 41

06N04756 2By61 5 41 50 48 45 12

06N04757 2B/Cy85 4 70 61 28 35 2

06N04758 2Cy178 20 81 44 15 36 4

06N04759 2Cy268 6 80 59 15 36 5

06N04760 2Cy371 1 50 27 38 72 12

PSA Cumulative Curve (Loam)

0

20

40

60

80

100

120

1 10

Size

Perc

ent

PSA Cumulative Curve (Silt Loam)

0

20

40

60

80

100

120

1 10

Size

Perc

ent

PSA Cumulative Curve (lvfs)

0

20

40

60

80

100

120

1 10

Size

Perc

ent

Bulk density Moisture state when volume is measured

should be specified.

1/3 bar bulk density - oven-dry mass per unit bulk volume of soil equilibrated at 1/3 bar (<2 mm) tension.• a. Clod method (primary method used by SSL),

provides ancillary data: COLE, water content at 1/3 bar.

• b. Reconstituted (plowed surface layer)

Bulk density Field moist bulk density – oven-dry mass

per unit of bulk volume of soil at field moisture• a. Compliant Cavity, frame, ring

(excavation techniques)• b. Known-volume can, field-moist core• (a. & b. <2mm / not natural fabric)

• Cores that are extracted without disturbing the natural fabric, and which remain in the core can be used for water retention.

• 2. Oven-dry bulk density - oven-dry mass per unit bulk volume of soil at oven dryness (<2 mm)

Other bulk density measurements

Oven dry bulk density - oven dry mass per oven-dry volume unit of soil

Rewet bulk density - used to determine irreversible shrinkage.

Bulk density relationships

1/3 bar bulk density is less than or equal to oven dry bulk density

There is less difference between clod and other methods in soils with less clay, more sand.

Bulk density relationships Average Db at 1/3 bar

• Soils g/cc Organic 0.05-0.35 Sandy 1.50-1.70Silty 1.30-1.60Clayey 1.20-1.40

Lab range for 1/3 bar / Db: 0.03 g/cc - 2.53 g/cc (>2.0 is unusual)

Bulk density average db values

clay_class db_13b(N) db_13b db_od(N) db_od

very-fine 1873 1.17 1907 1.49

fine 10689 1.36 10685 1.59

coarse silty 1089 1.4 1038 1.46

fine silty 5598 1.43 5604 1.56

fine loamy 8621 1.46 8504 1.57

sandy 4189 1.47 4013 1.51

coarse loamy 4842 1.47 4603 1.54

Water Retention

Determined by desorption on pressure plate.

Determined on 1)natural fabric clod /core or 2) <2mm

Water Retention 15-bar (1500 kPa) --ground soil <2 mm

• Approximate wilting point 2-bar (200 kPa)--ground soil <2 mm

• Approximate point at which plants begin to experience stress

1/3 bar (33 kPa) --natural fabric• Approximate field capacity

1/10 bar (10kPa)--natural fabric• Approximate field capacity in sandy soils

Appropriate sample types for water retention

Low tension (1/3 bar , 1/10 bar, - 6, 10, 33, 100 kPa) water retention determinations require clods for textures finer than sandy loam.

Higher tension (2 bar /200 kPa, 15 bar / 1500 kPa) can be determined on <2mm sieved samples.

15 bar to clay ratio ( > 5-10 percent clay)

Provides an indication of dispersion

Rule of thumb-- percent clay equals 2.5 times 15-bar water content minus percent organic carbon.

This may be used to estimate clay content in hard-to-disperse soils.

15 bar : clay ratio

For a typical soil with well dispersed clays, the ratio is 0.4. (If you remember no more, remember point four.)

Higher ratios indicate poor dispersion of clays.

Mollisols - Mineral Horizons - 15bar/clay

y = 0.472x

R2 = 0.6222

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100

Clay

15 b

ar

Alfisols - Mineral Horizons - 15bar/clay

y = 0.4351x

R2 = 0.7259

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70 80 90 100

Clay

15 b

ar

Andisols - Mineral Horizons - 15bar/clay

y = 1.2018x

R2 = -0.6483

0

10

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30

40

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70

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0 10 20 30 40 50 60 70

Clay

15 b

ar

15 bar to clay ratiosOther factors:

Low activity clays lower ratio to < 0.35 High activity clays increase the ratio Variable surface charge and amorphous

clay minerals Organic soils – higher 15bar : clay Other soils with dispersion problems,

salts, gypsum

Low activity clays, iron oxides, clay-sized carbonates produce 15 bar / clay of <0.4.

Ratios of less than 0.3 are common in some soils that contain large amounts

of gypsum.

Isotic mineralogy criteria

The ratio of 1500 kPa water to measured clay is 0.6 or more.

(Also NaF pH > 8.4 and no carbonates.)

15 bar water = .12 OC = 2% % clay = ______?

% clay = 2.5 x .12 +2 = 32%

15 bar water = .12 clay = .50

15 bar water = .23 clay = .27

.12 / .50 = .24 gypsum? Salts?

.23 /.27 = .85 andic?

Water relationships

Water is held at higher tension by smaller particles.

High tension water is held mostly in micropores (in interstitial spaces between soil particles): <2mm samples vs. clods can be used for 15 bar WR. There is no significant water in macropores at 15 bars.

Water retention different (WRD)

The difference between the 15 bar water content and the 1/10 or 1/3 bar water content on a volume basis• weight percent X bulk density = volumetric

water content

Soil Water Retention Curve

Silty Clay Loam

0

5

10

15

20

25

30

35

40

450

0.0

3

0.1

0.3

3 1 5 15

Suction in Bars

Pe

rce

nt

Wa

ter

wrd

Available Water Capacity (AWC)

The difference between field capacity and wilting point (Wilting point varies with the kind of crop.)

Water Retention Curve

Soil Water Retention Curve (<2mm)Longford Ap

0

10

20

30

40

50

0.001 0.01 0.1 1 10 100 1000

suction in bars

pe

rce

nt

/ 10

0

VG_vol_NASIS Gregson_volumetric

VG_vol_SSL SSL_vol

COLE Coefficient of Linear Extensibility

COLE –Coefficient of Linear Extensibility

1. When coarse fragments are absent (COLE ,<2mm, 1/3bar-oven dry ):

COLEwhole soil = (Dbd<2mm/Db33<2mm)1/3 – 1

Units = cm / cm

2. When coarse fragments are present (whole soil, 1/3bar-oven dry)

Coefficient of Linear Extensibility (COLE)

Determined using an undisturbed clod

Measures change in volume from 1/3 bar to oven dry.

COLE – soil paste / soil rod COLE rod = (Lw – Ld) / Ld

uses sieved < 2mm soil

the shrinkage of the soil paste was ~ twice that of the clod with a regression as follows: COLEstd = 0.0124 + 0.571 COLErod (r2 = 0.829). (Schafer and Singer, 1976)

Linear Extensibility Linear extensibility of a layer =

COLE x thickness of layer

Linear extensibility of a soil = sum of LE for all layers to 100 cm or root limiting layer

LE of 6.0 or more is a criterion for most vertic subgroups

Aggregate Stability

measures the retention of air-dry aggregates (2 to 1 mm) on a 0.5-mm sieve after sample has been submerged in water overnight followed by agitation of sample.

Reported as percentage of .5 to 2 mm aggregates retained after wet sieving.

Potential soil quality indicator.

Interpreting IRIS tube data

IRIS tubes can also be used to characterize reducing conditions for studies not specifically related to hydric soil determinations.

3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 500

10

20

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80

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100

Routon: BRUSHY SITE, % IRIS tube Fe removed

31246

31246b

31246c

31246c

31246d

depth (cm)

% F

e p

ain

t re

mo

ved

3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 500

10

20

30

40

50

60

70

80

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100

Site 161 (CORN FIELD): Percent Fe Removed from IRIS tubes

tube 1

tube 2

tube 3

tube 4

tube 5

depth: cm

% F

e p

ain

t re

mo

ved

3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 500

10

20

30

40

50

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100

Routon: WOODED SITE IRIS tubes % Fe removed

31266

31266b

31266c

32266d

depth (cm)

% F

e p

ain

t re

mo

ved

Exercise -- Hydrometer PSDA data spreadsheet

Cumulative Particle-Size Distribution Curve

(<75-mm base)

Exercise: Construct Distribution Curve

Plot measured values from 0.002 to 75 mm on semi-log paper

Sample number 88P3856 Data on pages 204, 209 Plot on chart obtained from National

Soil Mechanics Lab Show how to obtain intermediate values