A simplified parametric model to describe the magnitude and geometry of soil shrinkage

Summary Assessing the magnitude and geometry of soil shrinkage is indispensable for sound use and management of swelling and shrinking soils for agriculture and engineering. We have explored a simplified parametric model for the soil shrinkage characteristic curve, which is a measure for the magnitude of soil shrinkage, and tested it against experimental data for a Vertisol and a Lixisol under sugar cane in the Havana province, Cuba. We then applied the model to determine soil consistency limits, including the shrinkage, plastic and structural limits, using the model's third and fourth derivative. We further demonstrated how the model can be used to assess the geometry of shrinkage in terms of the relative crack area and the relative surface subsidence. Excellent matches were obtained between the observations and the fitted model. The shrinkage and structural limits corresponded to distinct changes in the soil shrinkage characteristic curve and were as such considered to be correctly estimated. The accuracy of the estimated plastic limit could, however, not been verified, since data were lacking. Linear regressions with R 2 > 0.88 were established relating the shrinkage and plastic limits to the soil's COLE index and the cation exchange capacity. The model could be easily applied to determine the crack area and the surface subsidence. We finally demonstrated how a geometry factor r s plays a crucial role in determining the shrinkage geometry, particularly for r s values ranging from 1 to 3.