Investigating the Relationship between Confined Compression Curve and Least Limiting Water Range

Least limiting water range (LLWR) is one of the important characteristics of the soil and is a soil structure identifier with difficult, costly and time-consuming measurement. Resistance to soil compaction is an index of soil organic matter, texture, structure and other properties which controls, the compression and its components and LLWR. So there is a correlation between the LLWR and compression curve, which has not been investigated so far. Since, the measurement of the confined compression curve is relatively quick and simple, therefore it can be used to estimate the LLWR. In this study, 24 disturbed and undisturbed soil samples were taken from West Azarbayjan and their soil water retention curves, soil penetration resistance curves and confined compression curves were determined. The ratio of silt to sand, the clay content, organic carbon, cation exchange capacity, calcium carbonate, aggregates mean weight diameter and confined compression parameters were used to estimate LLWR. The ability of each of the input variables, including confined compression characteristics, in improving the estimation of LLWR using regression models was evaluated. Using the confined compression parameters improved the estimation of the LLWR, significantly. Because, many characteristics affecting the confined compression are the same ones determining the LLWR. Relative improvement (RI) values were calculated for pedotransfer functions (PTFs) in suction 60 cm were 11.5, 19.7 and 28.53 % for PTF2, PTF5 and PTF7, respectively which showed considerable improvements in the estimation of LLWR by using confined compression and other properties as predictors. So, LLWR can be estimated with acceptable accuracy (R2=0.54) using confined compression parameters as estimators.