Effect of cultivation on the relationship between root length density and unsaturated hydraulic conductivity in a moderately swelling clay soil

Few studies have examined the effect of cultivation on the relationship between the presence of roots and unsaturated hydraulic conductivity in the soil matrix. Roots change soil pore characteristics by modifying pore diameter and pore continuity. Thus, the presence of roots may be expected to affect the hydraulic conductivity in saturated and unsaturated phases. In situ measurements of unsaturated hydraulic conductivity (Ku) at 0.04 m suction and root length density (Lv) of a moderately swelling soil were made in a wheat field and in a natural pasture field at 0, 0.25 and 0.4 m depths to determine their inter-relations. The Ku value decreased significantly with depth and the surface layer of the wheat field had the highest value (0.28 m day-1). The pasture field had high Lv at the surface layer (7.3 cm cm-3), but values decreased to less than those in the wheat field at 0.4 m depth. There was a distinct positive correlation between Lv and Ku, with the slope of the linear regression line being greater in the wheat field than in the pasture field. The cause of the relation is probably due to the common pore characteristics which influence Ku and Lv.