Soil Shrinkage Relationships of Texas Vertisols: II. Large Cores

Abstract

AbstractAlthough soil shrinkage in the field has been related to water content changes, this relationship has not been correlated with small core measurements or defined in terms of structural and shrinkage water loss phases. Since field measurements are limited by the accuracy of the water content determination, undisturbed cores (73 cm diam and 140 cm long) from the eight Vertisols studied previously were studied to accurately measure water loss (by weighing). Sorghum plants were established, and a single drying cycle was studied. Vertical shrinkage was measured at the surface and at the 15‐, 35‐, 55‐, 95‐, and 115‐cm depths, and the water content profile was measured with neutron moisture and gamma density probes. These data were interpreted in terms of the shrinkage pattern found in the cores and with the use of small core data obtained by Yule and Ritchie. (1980).Although the water loss data were confounded by large soil evaporation from shrinkage cracks at the side of the cores, the evidence suggested that the shrinkage response was a combination of structural and shrinkage water loss phases. Consequently, the shrinkage curve for the soil surface asymptotically approached the theoretical equidimensional, normal curve. Shrinkage curves with profile depth tended to parallel the soil surface curve. The water content profiles obtained were not precise, but shrinkage parameters calculated for various depth increments resembled the small core data obtained previously. The results showed that small core data could be used to predict field shrinkage responses if field soil water content profiles are known.