1. Spatial and Temporal Changes of Crack Formation of a Vertisol in the Texas Gulf Coast Prairie
Andrea S. Kishné, Cristine L. S. Morgan
Dept. Soil & Crop Sciences Texas A&M University, TX,USA
Wesley L. Miller
USDA Natural Resources Conservation Service, Victoria,TX,USA

2. Research Objectives Overall objective:
Quantify soil cracking processes to improve landscape hydrology models and USDA classification of Vertisols
Specific objective:
Analyze the relationships among microtopography, soil moisture, and spatial, temporal variation of crack patterns in a Vertisol on the Texas Gulf Coast Prairie.
Houston
Victoria
Study site

3. Piezometers
Laewest
Fine, smectitic, hyperthermic Typic Hapluderts
Soil moisture samples:
@ 10, 25, 50, 75 & 100 cm depth

5. Scanned and Rectified Study period: 1989 - 1998 42 crack diagrams
Scanning with 157 pixels/cm
18 dates of soil moisture Elevation measurements
10 m
Crack width categories, cm
≤ 0.5
0.5 ≤ 1.0
1.0 ≤ 2.0
2.0 ≤ 5.0
5.0 ≤ 7.0
10 m
10 m
10 m

6. Digitized Crack width categories, cm ≤ 0.5 0.5 ≤ 1.0 1.0 ≤ 2.0
≤ 0.5
0.5 ≤ 1.0
1.0 ≤ 2.0
2.0 ≤ 5.0
5 .0 ≤ 7.0
10 m

7. Crack Area Density for 100 m2
Below normal yearly precipitation
Normal yearly precipitation
0.02
Above normal yearly precipitation
Area density m2 m-2
0.01
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
Total Crack Area Density for 100 m2 over Time

8. Digital Elevation Model
Discretized thin plate spline
Cell size: 5 cm
RMSE: 1.3 mm, n=148
Contours
12.40 m
12.35 m
12.30 m
12.25 m
12.20 m
Calcareous puff
10 m

9. Slope 9 – 17 % 7 – 9 % 5 – 7 % 3 – 5 % 0 – 3 % Contours 12.20 m

10. Microhigh (38%)
Microslope (43 %)
Microlow (19 %)
Contours, m
12.40
12.35
12.30
12.25
12.20
10 m

11. Polylines Clipped by Micro-topo

12. Crack Area Density Micro-highs Microhighs Microslopes Microlows 0.05
Area density m2 m-2
0.03
Indicates month of July
0.01
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998

13. Micro-topography Crack Area
3.0
Microhighs
0.12
Microslopes
Crack area m2
2.0
Microlows
0.08
1.0
0.04 1 10 20 1 10 20 30 40
Sorted by Total Crack Area

14. Crack Density vs. Moisture Content2
0.04
0-10 cm
Micro-highs
N = 18
Micro-lows
Line density m m-2 1
Area density m2 m-2
0.02
0.15
0.30
0.45
0.15
0.30
0.45
Moisture content, kg kg-1

15. Monitoring Line Density
Increased
Decreased
Unchanged
10 m
Line density (m m-2) on 06/02/98
Line density (m m-2) on 07/20/98

16. Conclusions 1. Crack development starts on microhighs.
2. Crack density is greater on microhighs than on microlows at the same soil moisture content.
3. In 1998 crack density increased on micro-highs and decreased on microslopes and microlows.

17. Current Research
Analyze crack width and depth relationship to model crack volume
Develop empirical model between daily PET and crack development
Evaluate criteria of cumulative open crack periods in normal precipitation years for Usterts and Uderts in Soil Taxonomy
Compare the cracking sub-model of process-based landscape model to the measured crack data

18. Acknowledgements USDA-Natural Resources Conservation Service
Texas Agricultural Experiment Station
Dr. Raghavan Srinivasan and Todd Snelgrove at the Texas A & M University Spatial Sciences Laboratory