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

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

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

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

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

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

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

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

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

Polylines Clipped by Micro-topo

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

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

Crack Density vs. Moisture Content 2 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

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

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.

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

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