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Soil Aggregate Stability in Rangelands
Leonard Cratic
Mentor: Jeff Stone
USDA-ARS SWRC
UNIVERSITY OF
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Introduction
Erosion is a process which impacts the sustainability of rangelands.
There is a need to develop simple tools to evaluate sustainability of rangelands.
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Problem Statement
Two methods being used to estimate runoff ratio and erosion:
Direct measurement• Rainfall simulation• Expensive and time consuming
Indirect measurement• Slake testing• Measures soil aggregate stability• Quick and inexpensive
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Objectives
Assess the influence of plant cover on soil slake.
Determine whether correlations exist between soil slake and runoff and erosion.
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Methods
Rainfall simulation• Rainfall is applied to
a 2x6 meter plot and runoff and erosion is measured.
• Four plots per site
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Soil Aggregate StabilityMeasures how well a
soil ped retains its structure in water
• Soil stability kit• 18 samples per plot• Presence of plants
noted and soil samples ranked 1-6 (unstable-stable)
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Study Areas
Loamy Uplands ecological site– Soil-vegetation association
• 5 sites evaluated in Southeastern Arizona
• From observations– ER2 and KREE are most stable– ER4G and ER4S are moderately stable– ER3 is least stable
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Analysis
Slake evaluated using a t-test– Under and outside canopy– Among study sites
Regression analysis (slake vs. rainfall simulation)– Slake vs. runoff ratio
• Runoff ratio = runoff / precip.
– Slake vs. sediment yield• Sediment yield = sy / precip. / slope
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Under vs. Outside Canopy
a
b
1
2
3
4
5
6
Under Canopy Outside Canopy
Me
an
Sla
ke
Means are significantly different if letters are different
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Slake Among Sites
a
ab abc
bd
ae
1
2
3
4
5
6
ER2 ER3 ER4G ER4S KREESite
Me
an
Sla
ke
Means are significantly different if letters are different
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Slake vs. Runoff
Runoff = 0.77 + 0.01*Slake
R2 = 0.01*
0.0
0.2
0.4
0.6
0.8
1.0
1 2 3 4 5 6
Slake
Ru
no
ff R
ati
o
*Not statistically significant
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Slake vs. Sediment Yield
Sed Yield = 51 - 6.67*Slake
R2 = 0.24*
0
10
20
30
40
50
1 2 3 4 5 6
Slake
Sed
imen
t Y
ield
*Statistically significant
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Conclusions• Soil that was protected by canopy cover had more stable
aggregates.
• Significant differences in slake were between ER4S, ER2 and KREE.
• No correlation was found between slake and runoff ratio.
• A negative correlation was found between slake and sediment yield.
• The addition of more data will help to strengthen the validity of using slake testing for erosion assessment.
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AcknowledgementsSusan Brew
Jeff Stone
Chandra Holifield Collins
Rae Gomez-Pond
Jared Buono
Jonathan Krattickk Jakucki
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Thank You