Surface Cracking of a Vertisol Related to the History of Available Water

A previous study of a Vertisol with gilgai showed that soil cracking behavior proved difficult to represent using only current soil water content. However, soil moisture immediately preceding crack opening, called antecedent soil moisture, seemed to be an additional significant factor in explaining variations in surface cracking in field conditions. In this current study, the objective was to evaluate the effect of short- and long-term fluctuations of weather on surface cracking in this Vertisol using wavelet analysis. Soil cracking was monitored at a 100-m2 site of Laewest clay, a fine, smectitic, hyperthermic Typic Hapludert under native prairie vegetation in the Texas Gulf Coast Prairie during 1989 to 1998. Daily water availability index (WAI) calculated from precipitation and reference evapotranspiration was analyzed using discrete wavelet transformation. The data sets consisted of daily WAI values selected for 1024 d before 106 observation dates with and without cracks categorized according to gilgai microtopography. Long-term trend of WAI was separated from seasonal fluctuation using nonparametric kernel estimation. Discrete wavelet transformation was combined with multiple stepwise linear regression to identify time periods in history of available water that were significant (p < 0.01) for modeling crack area density. Data showed that WAI at time periods of 4 to 8 mo before crack measurements was significant in modeling cracking in addition to WAI at time periods corresponding to crack observations. Thus, results supported the hypothesis of the effect of antecedent moisture on the extent of surface soil cracking. Evidence also indicated significant WAI 1 and 2 yr before cracking.