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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
20
30
40
50
60
70
80
90
100
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
30
40
50
60
70
80
90
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
90
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
60
70
80
90
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