1. Rangeland Soil Health Indicators: Comparison of Soil Respiration and
Active Soil Carbon Field Methods
ABSTRACT
Estimating Rangeland Soil Health across large allotments requires tools and
techniques to quickly evaluate condition. Soil carbon and soil respiration are two soil
properties that are indicators of soil biological activity. Soil biological activity is an indicator
of overall soil health and function. The measurement of soil carbon and soil respiration is
often time consuming, requires laboratory methods, and can be expensive. In this study we
test two low cost field methods for estimating soil carbon and soil respiration and compare
those indicators to other soil properties. Soil carbon estimates were found to be correlated
with soil respiration. The soil carbon tests also correlated well with soil respiration for
differences in soil texture, soil stability, and rangeland vegetation. Correlations of soil
carbon and soil respiration were not as high for aspen and oak/maple cover types. We offer
suggestions as to the use of both methods in estimating soil health and condition for
rangeland ecosystems of the west.
Study Objectives:
1. Determine suitability of Active Carbon and Soil Respiration as indicators of rangeland
health
2. Compare field methods of KMnO4 for active carbon and Solvita Gel for soil respiration
Soil Measurement Methods
The soil measurement methods tested were:
Soil Organic Carbon Potassium Permanganate method.
Soil Respiration Biological CO2 Respiration method by Solvita.
Robert Davidson, Soil Scientist1; Jeff Bruggink; Regional Soil Scientist2; Jan Curtis-Tollestrup, Hydrologist1; Alexandra Schuetter, Hydro Tech1; and Greg Brown, Hydro Tech1
1U.S. Forest Service, Region 4, Manti-La Sal NF, Watershed Program Group, Price, Utah, 2 U.S. Forest Service, Region 4, Intermountain Region Office, Ogden, Utah, UT
SAMPLING METHODS
Sampling of soils was conducted from June through September 2015. The sampling of
soils was completed on the Manti La Sal National Forest in central Utah. The
following restrictions and methods were used during sampling:.
 Representative range sites were visited across the forests. Dominant soil types were
sampled within the representative range sites
 Sampling design was biased to locations where representative vegetation for the range site
was present.
 A limited number of sample sites were collected due to distance and time limitations for the
single field season study.
 A total of 46 sites were sampled. Soil was collected as composite samples of the A horizon
for each site. Resulting in 46 soil samples for analysis.
 6 Range vegetation types were sampled
 Mountain big sagebrush, Mountain shrub, Grassland, Aspen, Oak/Maple, Forb
 Both the active carbon and soil respiration methods were used at each of the 46 sites.
All 46 sites were analyzed for active carbon and soil respiration. Samples were
analyzed in triplicate for each site and averaged for active carbon and soil
respiration. In addition the following were collected at each site: Ground cover %,
bare soil %, soil compaction estimate, cover type, soil stability rating, parent material,
% rock fragment, pH, soil color, texture, effervescence, structure, consistence, slope,
aspect, and landscape position.
Potassium permanganate
method measures active carbon
that is oxidized by the KMnO4. It
is an indicator of carbon change
in the soil that may be due to
management. It is measured by
a color change of the soil
sample. The more carbon the
greater the color change. The
procedure is best completed
indoors to ensure consistency
with soil samples but it can be
used in the field for general
estimates.
Soil Respiration was measured
using Solvita Gel that provides
and estimate of CO2 lost by the
soil. Microbial activity in the soil
releases CO2 which is absorbed
by the Solvita gel on “paddles”
that are inserted within a sample
jar with soil. A color change
occurs with the gel paddles that
is measured for amount of CO2
absorbed
General Location of Manti
La Sal National Forest, Utah
Sample Site Locations Across Allotments
Within The Manti La Sal National Forest, Utah
Mountain Big Sagebrush Range Type
Grassland Range Type
Oak/Maple Range Type
Aspen Range Type
Mountain Shrub Range Type
Forb Range Type
Low Carbon-Low Soil Respiration Soil High Carbon-High Soil Respiration Soil
The KMnO4 method was first compared to the Solvita Gel as a general
indicator of soil condition. Where there similar changes to active carbon and
soil respiration between sites with each method? Figure 1 below shows there
was a moderate correlation between active carbon and soil respiration using
the two separate methods. Figure 2 is a site by site comparison of results of
the two treatments put onto a continuous line graph. This graph shows that for
the majority of sites the active carbon and soil respiration had corresponding
differences from site to sites. Meaning both methods were capturing soil
differences between sites and the differences were similar in positive/negative
changes.
Figure 1. Correlations of KMnO4 Active Carbon Results to
Solvita Gel Soil Respiration Results
Figure 2. Plot by Plot Comparison of KMnO4 Method for Active
Carbon and Solvita Gel for Soil Respiration in the Ability to
Estimate Differences in Soil Properties
Each method was compared to general vegetation cover type to determine
relationships of active soil carbon and soil respiration to soil/plant community types.
The average A horizon mg C/kg soil for the active carbon (Figure 3) and mg CO2/kg
soil for soil respiration (Figure 4) were determined for each soil/plant (range type)
sampled. The results showed there are greater similarities with the field methods
tested in the non forested ecosystems with active carbon and respiration and less
consistency in the aspen and oak/maple ecosystems.
Figure 3. KMnO4 Active Carbon Method Average Results by
Range Type
Figure 4. Solvita Gel Soil Respiration Method Average Results by
Range Type
Soil texture can significantly affect active carbon accumulation as well as soil
respiration rates. Both field methods were compared to the sampled soil field
texture for determining any observed relationships to soil texture. As shown in
Figures 5 and 6 below both the Active Carbon Test and the Soil Respiration test
responded similarly to differences in soil texture. However, the soil respiration test
appeared to be more sensitive to changes in soil texture.
Figure 5. Average Active Carbon Within A Horizons By Soil Texture
Using KMnO4 Method
Figure 6. Average Soil Respiration Within A Horizons By Soil Texture
Using Solvita Gel Method
RESULTS DISCUSSION
Every sample site was assigned a soil stability rating. The soil stability
rating ranged from unsatisfactory/unstable to satisfactory/stable soil
stability. It is based upon a modified slake test using the method described
in the Monitoring Manual for Grassland, Shrubland and Savanna
Ecosystems Vol. 1 Ver. 2 (Herrick et.al. 2015, USDAARS Jornada Exp.
Range). The test reflects the biotic integrity of the soil and ability of the soil
to resist erosion due to water. A small ped from the surface 1-2 inches of
mineral horizon was used for the soil stability test. Figures 7 and 8 show
the comparison of the active carbon and soil respiration tests to the
observed soil stability results. Both the active carbon and soil respiration
test showed a positive correlation to soil stability. The greater the soil
stability the greater the active carbon and soil respiration.
Figure 7. Correlation of Active Carbon Test to Soil Stability Test Figure 8. Correlation of Soil Respiration Test to Soil Stability
Test
COMPARISON OF METHODS
RECOMMENDATIONS
# Both methods are acceptable to measure soil indicators of biological activity.
# The KMnO4 is less expensive and easier to run many samples and duplicates of samples.
# The tests can be done in the field with the KMnO4 but we recommend all tests are done with
oven dried soils indoors.
# They can be used for key areas to show trend or to compare a reference site to an area in
question. Repeat tests should be taken at the same time of the year.
# We do not recommend either method as a general assessment protocol without any type of
comparison to a reference soil at the same time. There are no thresholds established for
data/results with single site samples.
# Total costs for 20 samples: KMnO4 $500-800, Solvita Gel $800-1100.
# The KMnO4 does require handling of concentrated KMnO4 and additional safety
equipment is required.
# The Solvita respiration test can provide additional information on the nitrogen availability
of the soil.
# Both methods are affected by season of year. Solvita probably more affected by changes
throughout the year.
#The Solvita respiration test is easier to use but near double the total costs.
Choosing Appropriate Soil Quality Indicators to Determine Rangeland
Condition