Estimation of water-retention characteristics from the bulk density and particle-size distribution of Swedish soils

A Swedish soils database containing soil-water retention data, particle-size fractions, dry bulk. density, and organic matter content was analyzed in order to find a relatively simple predictor of the soil-water retention curve (SWRC), As a SWRC model we chose a three-parameter function selected hom nine van Genuchten-type retention models that were fitted to the measured retention data by nonlinear parameter optimization. Cumulative particle-size (CP) data were described by a logistic distribution model, Additionally, the mean and standard deviation of the CP distribution were estimated directly from the measured particle-size data, Regression equations were subsequently used to estimate the parameters in the selected SWRC model from available soil properties, particle-size data, and CP distribution parameters, Four alternative pedotransfer models were formulated to estimate the SWRC curve from the basic soil properties, These models predicted the SWRC curves from either the original soil data or from the CP distribution parameters, A mean estimation error of less than 2.5% was used to indicate a good estimation, The highest ratio (67%) of good estimations and the lowest ratio (12%) oh poor estimations were obtained when both the original soil properties and the CP model parameters were used, Our study shows that the resulting simple SWRC model gives a good description and a usable prediction of the retention properties of Swedish soils for a wide range of soil textures.