Measuring soil hydraulic properties like hydraulic conductivity and soil water retention curves is difficult to do correctly. Measurements are affected by spatial variability, land use, sample prep, and more. Getting the right number is like building a house of cards. If one thing goes wrong—you wind up with measurements that don’t truly represent field conditions. Once your data are skewed in the wrong direction, your predictions are off, and erroneous recommendations or decisions could end up costing you a ton of time and money. Learn common mistakes to avoid and best practices that will save you time, increase your accuracy, and prevent problems that could reduce the quality of your data. Topics covered: - Sample collection best practices - Where to make your measurements - How many measurements you need - Field mapping tools - How to get more out of your instruments - How to use the LABROS suite to fully characterize soils (i.e., full retention curves and hydraulic conductivity curves) - Best practices for measuring field hydraulic conductivity using SATURO

2. SOIL HYDRAULIC PROPERTIES
8 WAYS YOU CAN UNKNOWINGLY
COMPROMISE YOUR DATA
Leo Rivera
METER Group, Inc. USA

3. INTRODUCTION
ABOUT ME
Background in Soil Physics &
Pedology
12 years of experience measuring
and interpreting soil hydraulic
properties and soil moisture
release curves

4. SOIL HYDRAULIC PROPERTIES
WHY DO WE CARE ABOUT IT?
It impacts almost everything
soil is used for
• Crop production
• Irrigation & drainage
• Hydrology (native & urban)
• Landfill performance
• Stormwater system design
• Soil health

5. COMMON ISSUES
WHEN MEASURING
SOIL HYDRAULIC PROPERTIES
Sample collection
Field vs. lab measurements
Measurement location & number
Measurement quality

6. GOALS
• How many measurements you need
• Where to make your measurements
• Field mapping tools
• Sample collection best practices
• Tips for using the LABROS suite
• Best practices when using the SATURO in the field

7. SOIL HYDRAULIC PROPERTIES
WHAT HAS AN IMPACT?
Soil texture
Soil structure
Biopores
Compaction/bulk density
Water content/potential
Organic matter

8. HOW MANY MEASUREMENTS?
Accounting for spatial variability
Representative Elementary Volume (REV)
• The smallest volume of soil that can represent
the range of microscopic variations
• For water flow processes, REV is based on soil
structure
Time domain or seasonal changes
• Antecedent soil moisture
• Changes in vegetation
• Land-use impacts
Research specific needs
• Number of treatments or plots
• Different locations
• Amount of variation that needs to be
characterized
Instrument measurement volume
• Sample core size
• Infiltrometer ring size
• Practical limitations

9. WHERE SHOULD I MEASURE?
Factors to consider
• Number of treatments
• Different locations
• Changes in soil type
• Topography/landscape position
• Land use
• Field traffic

10. FIELD MAPPING TOOLS
ELEVATION MAPS
Soil formation processes differ due
to landscape (Catena concept)
GIS tools & existing data
Easy to visually identify

11. FIELD MAPPING TOOLS
ELECTRICAL CONDUCTIVITY MAPS
Tools that measure apparent
soil electrical conductivity (ECa)
help identify variability
Soil properties affect ECa
• Salinity
• Depth to parent material
• Soil texture
• Clay type
• Soil moisture

12. FIELD MAPPING TOOLS
SOIL SURVEY
Free tools through USDA-NRCS
Larger scale of observation

13. SAMPLE COLLECTION
BEST PRACTICES
Intact vs. repacked cores
• Soil structure
Record site information
• Location (GPS coordinates)
• Bulk density
• Antecedent soil moisture
• Vegetation
Rocks & roots
Collect duplicate samples
Expansive soils
• Sample when soil is near field
capacity

14. MEASUREMENT
BEST PRACTICES

15. LAB VS. FIELD MEASUREMENTS
Strengths Limitations
Lab
Instrumentation
• Controlled conditions
• Run samples directly
• Automated and relatively fast analysis
• Defined procedure
• Accuracy
• Doesn’t take field conditions into
account
• Complicated setup with some systems
Field
Instrumentation
• Understand variability and real time
field conditions
• Easy installation and setup
• Automated measurements
• Cellular technology enables near real-
time soil sensor data collection from
the office
•Variability requires more measurements
•More data to analyze
•Uncontrolled conditions
•Unpredictable weather can cause delays
and damage unprotected equipment
•Poor installation can cause inaccuracy
https://www.metergroup.com/environment/articles/lab-vs-field-instruments-why-you-should-use-both/

16. LAB MEASUREMENT
BEST PRACTICES
(LABROS)

17. LABROS BEST PRACTICES
UNDERSTANDING LIMITATIONS
Sample volume typically small
No instrument covers full range
Measuring Ksat vs Kψ

18. LABROS BEST PRACTICES
WHICH PROPERTIES ARE CRITICAL
What range of water potential is
critical?
What range is the water being
held?
• Coarse vs. fine-textured soils
Unsaturated vs. saturated
hydraulic conductivity
0
10
20
30
40
50
60
0.1 1 10 100 1000 10000 100000 1000000
VWC,𝝷𝝷
MATRIC POTENTIAL, -KPA
LFS (HYPROP) LFS (WP4C) LFS (Fitted Curve)
SiL (HYPROP) SiL (WP4C) SiL (Fitted Curve)

19. LABROS BEST PRACTICES
UNDERSTANDING LIMITATIONS
Field measurements:
Complete soil interaction
Lab measurements:
Single-point assessment

20. LABROS BEST PRACTICES
FULL CHARACTERIZATION
Accounting for hysteresis
• Wetting vs drying curves
Evaporation method (drying curve)
Vapor pressure methods (wetting & drying)
Sampling from HYPROP sample

21. LABROS BEST PRACTICES
SUBSAMPLING FROM HYPROP
Subsample from both ends of core Sample from inner sections of sample

22. LABROS BEST PRACTICES
FULL CHARACTERIZATION
Matric (ψm) vs. Osmotic potential (ψo)
• Tensiometer methods measure ψm
• Vapor pressure methods measure ψm+ ψo
Correct of ψo with saturated extract EC

23. FIELD MEASUREMENT
BEST PRACTICES
(SATURO)

24. SATURO BEST PRACTICES
Pre-field checklist
• Tools
• Selecting a water source
• Site characterization sheet
Site selection
• Large rocks & roots
• Expansive soils

25. SATURO BEST PRACTICES
Measurement site preparation
• Trim tall vegetation
• Remove large debris
5 cm vs. 10 cm insertion ring
• Soils structure
• Duff layer
Ring insertion
• Prevent air gaps

26. SATURO BEST PRACTICES
3-dimensional flow corrections
• Estimating lateral flow
Dual-head pressure method settings
• Soil type
• Antecedent soil moisture
• Macropores
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1
7
13
19
25
31
37
43
49
55
61
67
73
79
85
91
97
103
109
115
Flux(cm/s)
Time (min)

27. SUMMARY
KEYS TO A GOOD MEASUREMENT CAMPAIGN
Take enough measurements to quantify variability (REV)
Know where to measure
Utilize field mapping tools to make that decision
Collect quality samples
Follow appropriate best practices for your instrumentation

28. QUESTIONS