Shrinkage-swelling characteristics and plasticity indices of paddy soils: spatial variability and their influential parameters

Abstract

ABSTRACT Shrinkage-swelling behavior and plasticity indices of paddy-soils of the Guilan province, Iran, their spatial variability and influential parameters were evaluated. Coefficient of linear extensibility (COLE), shrinkage index (SI), shrinkage (SL), plastic (PL), and liquid (LL) limits, plasticity index (PI), and the dimensionless geometry factor (rs) of deformation, cation exchange capacity (CEC), organic carbon (OC), saturated water content (θs), bulk density (BD), particle density (PD) and soil texture were determined. SI and COLE had extremely strong and LL and PI had strong positive correlations with θs. The significant effect of clay, CEC, OC and θs on Atterberg limits, COLE, and SI indicated their great impacts on soil strength in tillage and engineering applications of soils. Multiple-regression models could explain 97%, 92%, 76%, 61%, 55%, and 32% of the variations in COLE, SI, LL, PL, PI, and SL, respectively. Isotropic spherical and exponential models were the best-fitted models for the variograms. CEC and OC showed strong spatial structure, while PL and the remaining traits showed weak and moderate structure, respectively. All the soils with rs < 3 showed moisture-dependent anisotropy of vertical and horizontal deformation. Generally, the paddy soils had medium to high shrinkage capacity and vertical deformation was dominant during the shrinkage process.