SOIL SCIENCE
TEXAS A&M UNIVERSITY
SOIL SCIENCE
TEXAS A&M UNIVERSITY
ARPA-E Workshop
Novel Methods for
Phytosequestration
July 23-24, 2015
SOIL COMPOSITION, SOIL VARIABILITY, AND
PROXIMAL SOIL SENSING OF SOILS
CRISTINE MORGAN | PROFESSOR OF SOIL SCIENCE
DEPARTMENT OF SOIL & CROP SCIENCES
SOIL SCIENCE
TEXAS A&M UNIVERSITY
Outline
o Introduction to soil properties & composition
o Current tools for proximal sensing
o Spatial Variability, Precision/Accuracy
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TEXAS A&M UNIVERSITY
Soil as a 3 + 1 phase system
Solids
Liquids
Gas
+ Roots
Imaging the soil requires discrimination
between the soil phases
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TEXAS A&M UNIVERSITY
Fundamental soil properties
Solids
Bulk Density/Porosity
Soil Minerals (Physical)
•Particle Size Distribution
•Mineralogy of silicate clays
•Mineralogy of size-fractions
Soil Minerals (Chemical)
•Cation Exchange Capacity
•Exchangeable Cations and Ions
•pH
Organic Carbon
Liquids
Water-filled pore space
Water-filled pore space as a
function of matric potential
Extractable water chemistry
Gasses
Air-filled pore space as a
function of water content or
potential
Gas Composition
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TEXAS A&M UNIVERSITY
Fundamental soil properties
Soil Minerals (Physical)
Particle Size Distribution
sand 2.0 to 0.05 mm
silt 0.05 to 0.002 mm
clay < 0.002 m
Any Fraction: Carbonates, Gypsum, Salts
Clay Fraction: Silicate clays (2:1 and 1:1 clay silicates)
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TEXAS A&M UNIVERSITY
Fundamental soil properties
Soil Minerals (Chemical)
• Cation Exchange Capacity
• Sandy Soil 3 to 5 meq 100g -1
• Clayey Soil 30 to 40 meq 100 g-1
• pH
5.5 to 8.5 (Temperate Agricultural Soil)
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Soil Organic Carbon
0.5 to 4 % Soil Organic C in topsoil of majority of temperate agricultural soil
Fundamental soil properties
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Organization of Soil in the Field
Soil Structure: Related to the arrangement
and organization of the soil
phases
Affects: Pore-network connectivity,
tortuosity
Bulk Soil
Bulk Density 1.0 to 1.62 g cm-3
root limiting ~ 1.3/1.5 1.7-for sure!
Porosity 0.62 to 0.38 % pores by vol.
root limiting ~ 0.38-0.35
Courtesy of the NCSU Soil Science Flickr Stream
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TEXAS A&M UNIVERSITY
Proximal Sensing
High resolution surface (x,y) mapping High resolution profile mapping (z)
Surfing Diving
0 20 40 60
100
80
60
40
20
0
Clay content, %So
il d
ep
th, cm
e.g. Waiser et al. 2007; Ackerson et al. 2015
e.g. Christy, 2008; Bricklemyer and Brown 2010
Image from Veris Technologies
Proximal Sensing: non destructive, field-located sensing of soil properties
SOIL SCIENCE
TEXAS A&M UNIVERSITY Field Measurements:
Electromagnetic Induction
ECa = ECliquid phase + ECsolid phase
SOIL SCIENCE
TEXAS A&M UNIVERSITY Field Measurements:
Penetrometer Mounted VisNIR DRS
0
0.1
0.2
0.3
0.4
0.5
0.6
350 700 1050 1400 1750 2100 2450
Wavelength
Re
fle
cta
nc
e
Clay Content (RMSE 5 %)
Organic Carbon (RMSE 0.5 %)
Inorganic Carbon (RMSE 0.8 % )
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Field Measurements:Electrical Resistivity Tomography
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TEXAS A&M UNIVERSITY
Case study: ERT in Vertisols
Cracking soils
Non destructive/temporal measurements of
1. Soil water content
2. Crack volume and location
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Laboratory Data
Field Data
ERT and Soil Water Content
Poor contrasts between soils at
different water contentAckerson et al., 2014
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TEXAS A&M UNIVERSITY
R² = 0.5019
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.4 0.6 0.8 1R
esis
tivity
[Ωm
]
105
104
101
102
103
Cra
ck P
oro
sity [
m3m
-3]
Relative Resistivity
ERT and Cracking
Strong contrast
between cracks & soil
Ackerson, 2014
SOIL SCIENCE
TEXAS A&M UNIVERSITY
Spatial Variability
Soil properties vary at all spatial scales
Soil properties that affect soil organic C at the watershed (km) and field (m) scale include
- Texture (particle Size distribution)
- Topography characteristics (wetness index/drainage)
- Soil condition
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TEXAS A&M UNIVERSITY
Summary
The efficacy of imaging or sensor technology is soil dependent
Electromagnetic Induction: good for spatial structure of soil change
VisNIR: good for point-profile measurements e.g. soil organic C spatial variability and stock (precision is 0.5 % SOC)
ERT: good for monitoring change over time
Soil function in the field determines the efficacy of ERT
- Poor measurement of water content
- Good measurement of cracking