Predicting saturated hydraulic conductivity by soil parametric and morphological properties

Numerous of studies have been conducted to describe soil saturated hydraulic conductivity (Ks) by soil parametric properties such as bulk density, texture, organic matter, and particle-size distribution. However, although soil morphological properties have a strong effect on Ks, studies targeting at describing relation between Ks and soil morphological properties such as type, size, and strength of soil structure; type, orientation and quantity of soil pores and roots; consistency; and plasticity are rare. This study aimed at evaluating soil morphological properties along with soil parametric properties to predict Ks. The study was conducted on paddy soils and adjacent grasslands on Kızılırmak Township (near the town) of Cankırı Province. Undisturbed soil samples were collected from sixty randomly selected sampling sites from topsoil (0-15 cm) and subsoil (15-30 cm) (120 samples) with plastic soil samplers (15 cm length and 8.0 cm id.) connected to an apparatus mounted to three-point system of a tractor. Synchronized disturbed soil samples were taken from the same sampling sites and depths for basic soil analyses. Saturated hydraulic conductivity was measured on the soil columns using a constant-head permeameter. Following the Ks measurements, the upper part of soil columns were covered to prevent evaporation and colums were waited in the laboratory. When the water flow through the column was stopped, samplings were taken for bulk density and penetration resistance was measured on the columns. Then, the soils were disturbed and morphological properties of soil color, soil structure, pores, roots, consistency, and plasticity were described by standard soil description charts used in soil survey studies. In addition, soil texture, bulk density, soil reaction (pH), field capacity, wilting point, cation exchange capacity, specific surface area, aggregate stability, organic matter content, and calcium carbonate were measured on the synchronized disturbed soil samples. Laboratory measured Ks-values had a mean of 0.83 cmh-1 and changed between 2.71 and 0.0036 cm h-1. Greatest variability ocurred for Ks (80%) and lowest for pH (5.6%) for soil parametric variables; and greatest variability ocurred for root amonut (61%) and lowest for structure class for morphometric properties. The measured Ks values were correlated to soil parametric and morphological properties by multiple linear regressions. Stickiness, soil structure grade, pore size, plasticity, and pore quantity significantly correlated to Ks. Linear multiple regression equation developed using these properties, described 94% total variation in Ks, and measured and predicted Ks values were significantly correlated with each other (r=0.95). The results showed that soil morphological properties, that readily available in soil survey databases, can be used along basic soil properties in predicting soil dynamic processes.