Soil Aggregate Stability in Rangelands
Leonard Cratic
Mentor: Jeff Stone
USDA-ARS SWRC
UNIVERSITY OF
Introduction
Erosion is a process which impacts the sustainability of rangelands.
There is a need to develop simple tools to evaluate sustainability of rangelands.
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
Objectives
Assess the influence of plant cover on soil slake.
Determine whether correlations exist between soil slake and runoff and erosion.
Methods
Rainfall simulation• Rainfall is applied to
a 2x6 meter plot and runoff and erosion is measured.
• Four plots per site
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)
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
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
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
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
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
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
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.
AcknowledgementsSusan Brew
Jeff Stone
Chandra Holifield Collins
Rae Gomez-Pond
Jared Buono
Jonathan Krattickk Jakucki
Thank You