Antecedent soil moisture affecting surface cracking of a Vertisol in field conditions

Cracking of shrink–swell soils influences landscape hydrology. Watershed models that address soil cracking phenomena generally use a relationship between shrinkage and current soil water content to estimate the extent of cracking. Although antecedent soil moisture prior to soil shrinkage is found to affect the shrinking of expansive soils in laboratory measurements, field observations are limited. In a previous study, a series of in situ surface crack measurements over 10 years indicated the effect of soil moisture just prior to the start of cracking (antecedent soil moisture) on cracking extent, but this relationship was not specifically analyzed. The objectives of this study were (i) to estimate the antecedent soil water content prior to cracking, (ii) to analyze the effect of antecedent moisture on crack area density in microhighs and microlows, and (iii) to assess the temporal distribution of antecedent soil moisture in relation to an estimated water availability index. Soil cracking was measured on a 10-m × 10-m plot of Laewest clay (fine, smectitic, hyperthermic Typic Hapludert) covered with native tallgrass vegetation on 42 dates during 1989–1998. Gravimetric soil water content was measured on 50 dates; 18 dates corresponded to crack measurements. Gilgai microtopograhy was mapped, and surface crack area density was calculated. For days when soil water content was not measured, it was estimated from precipitation and evapotranspiration. Antecedent soil water content prior to cracking was estimated for depth at 10 cm using daily estimates of soil water content and field notes on cracking. Results indicated that the temporal variation in surface crack area density of the study area during 10 years was related to dynamics of current and antecedent soil water content on microhighs and microlows ( R 2 = 0.68 and 0.59, respectively). Prediction accuracies improved with classifying drying–wetting conditions during cracking. Dynamic temporal changes in the surface crack area density exhibited dependence on a long-term (multi-year) cycle of antecedent soil water content superimposed by short-term (within a year) cycles of current soil water content.