Assessing Soil Health in Missouri
Agricultural Soils
Kristen Veum
Robert Kremer
Keith Goyne
Soil Health Workshop. Bradford Extension and
Research Center. Oct. 8, 2013
Soil Sampling Considerations
When, Where, How, & Why
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Why? Most important consideration.
When?
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Where?
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Time of year (seasonal, management activities)
Across years (trends)
Management Practice Comparisons & Reference Soil
Comparisons (fence row, uncultivated soil)
Landscape Position / Landforms / Soil types
Rhizosphere, Depth differences
How?
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Soil sampling and handling/storage protocols
Biological Soil Properties
Biological properties can change rapidly
(dynamic):
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Spatially
• Depth – generally decline with depth
• Landscape (rhizosphere, hillslope)
Temporally
• Season
• Crop and other management activities
• Climate differences (i.e., drought
years)
• Short-term and long-term trends
What is a soil quality/health index?
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Goal: Translating soil properties into a soil quality or
soil health score.
How?
• Measure important soil properties (i.e., soil health
indicators)
• Assign a score based on relationships with soil
functions (water infiltration, crop productivity, etc…).
• General Categories: More is Better, Less is Better,
Optimal Value
• The scores are combined into one final number.
Each existing soil health index uses a unique set of
soil properties and a unique way of scoring soil
health. Some are quantitative, some are very
subjective. Many are region-specific.
Soil Quality/Health Indices
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Soil Management and Assessment Framework (SMAF)
soil quality index
Cornell Soil Health Test (CSHT)
Assessing Agronomic and Environmental Performance of
Management Practices in Long-Term Agroecosystem
Experiments (AEPAT)
Soil Conditioning Index (SCI)
Biological Quality of Soil (QBS)
CCME Soil Quality Index (SoQI)
Forest Soil Quality Index (FSQI)
The Soil Management Assessment
Framework (SMAF) soil quality index
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Scores based on data linking soil indicators to soil
functions, such as crop productivity, water infiltration, and
environmental protection.
Based on site-specific characteristics that account for
important factors such as crop, climate, soil texture,
mineralogy, etc.
13 indicators representing 4 soil function groups:
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Physical – aggregate stability, bulk density, water filled pore space,
available water capacity
Chemical – electrical conductivity, pH
Nutrient – P, K, Na adsorption ratio
Biological – SOC, microbial biomass-C, β-glucosidase, mineralizable
N
SMAF Example: Centralia Plots (2008)
5 Cropping Systems (since 1991):
• Minimum Till Corn – No Till Soybean (MTC-NTS)
• No Till Corn – No Till Soybean (NTC-NTS)
• Integrated Crop Mgt - Wheat (cover) - Corn
(cover) – Soybean (ICM-WCS)
• Switchgrass formerly intensively cropped (SG)
• Cool-season grass & legume (CRP)
3 Landscape Positions:
• Summit, Backslope, and Toeslope
SMAF Example: Centralia Plots
6 SMAF Indicators Selected (of 13)
**You do not need to measure all possible
indicators in order to use an index
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Soil Organic Carbon
Extractable Phosphorus
Extractable Potassium
Water pH
Bulk Density
Water Stable Aggregates
Centralia SMAF Scores by
Landscape Position
Clear landscape position differences in SMAF scores
Soil Organic Carbon (SOC)
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Measure of organic
matter
Source of many important
nutrients
Affects cation exchange
capacity, water holding
capacity, soil
aggregation, etc.
Considered a ‘keystone’
soil health property
Soil Organic Carbon: Cropping Systems
Measured Values and SMAF scores
Clear effects of cropping
system in SOC data and
SMAF SOC scores.
CRP has highest SOC and
SOC score. The switchgrass
still reflects the degradation
from previous intensive
management
Soil Organic Carbon: Landscape Positions
Measured Values and SMAF scores
Clear effects of landscape
position in SOC data and
SMAF SOC scores
The increased clay content
of the backslope changes soil
texture and affects
the SMAF score
Microbial Enzyme Activity
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measures the function of the microbial
community
reflects the quantity and quality of
available substrates
different enzymes represent
decomposition and cycling of different
nutrients
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phosphatase – phosphorus
nitrogenase – fix nitrogen
dehydrogenase – overall microbial activity
β-glucosidase – breakdown of cellulose, etc.
β-Glucosidase: Cellulose degradation
Measured Values and SMAF scores
Clear effects of cropping
system from disturbance
The “more is better” concept
translates greater enzyme
activity into higher SMAF
scores
CRP>Cover>No-till>=
SWG>MinTill
Water Stable Aggregates
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Reflects soil structure and
resistance to erosion, slaking,
etc.
Tends to be stronger with
increased clay and organic
matter
Extremely important for water
infiltration, aeration, etc.
Water Stable Aggregates:
Measured Values and SMAF scores
Clear effects of
cropping system in
aggregate stability.
Trend relates to soil
disturbance
SMAF scores all fairly
high. This is due to the
way SMAF scores
aggregate stability.
Water Stable Aggregates:
Measured Values and SMAF scores
Clear effects of
landscape position in
aggregate stability.
Clay and organic
matter are important
in soil aggregation.
The scores reflect the
SMAF algorithm…..
Bulk Density
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Increases with
compaction from traffic - can increase with no-till
compared to
conventional tillage
Increased bulk density is
associated with reduced
aeration and water
infiltration
Bulk Density
Measured Values and SMAF scores
The “less is better”
concept translates
greater bulk density
into lower SMAF scores.
Switchgrass has the
highest bulk density due
to previous intensive
cropping practices
Overall SMAF Scores by Cropping System
Mineralizable Nitrogen
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Is a subset of total N
Sometimes called the ‘active N
fraction’
Supplies N for crop growth
Mineralizable Nitrogen: By Depth
Measured Values and SMAF scores
Centralia (2010 data):
Surface 0-10 inches
Subsurface 10-20 inches
Depth differences for raw
data and SMAF scores.
Illustrates the decline in
biological properties with
depth.
Consider how perennial
vegetation differs from annual
cropping systems…
Does the SMAF Work?
Sanborn Field Example
Veum et al. 2013 (Biogeochemistry)
Why can’t we just measure one
variable for soil health?
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Each soil health indicator tells us something
important about the soil
A soil may perform some functions well but not
others
Together, the soil health indicators tell a more
comprehensive story about the soil
Necessary to make more informed management
decisions.
Many Important Variables not currently in the
SMAF or other soil health indices
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Active C
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Phospholipid Fatty Acids
(PLFA)
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Cornell Soil Health Test
tomorrow’s talk
Other microbial enzymes
Need more biological
variables in soil health
indices
Selected SMAF References
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Stott, D.E., C.A. Cambardella, R. Wolf, M.D. Tomer, and D.L. Karlen. 2011. A
soil quality assessment within the Iowa River South Fork Watershed. Soil
Science Society of America Journal 75:2271-2282.
doi:10.2136/sssaj2010.0440.
Stott, D.E., S.S. Andrews, M.A. Liebig, B.J. Wienhold, and D.L. Karlen. 2010.
Evaluation of β-glucosidase activity as a soil quality indicator for the Soil
Management Assessment Framework (SMAF). Soil Science Society of
America Journal 74:107-119. doi:10.2136/sssaj2009.0029.
Karlen, D.L., G.E. Varvel, J.M.F. Johnson, J.M. Baker, S.L. Osborne, J.M.
Novak, P.R. Adler, G.W. Roth, and S.J. Birrell. 2011. Monitoring soil quality
to assess the sustainability of harvesting corn stover. Agronomy Journal
103:288. doi:10.2134/agronj2010.0160s.