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