Journal of Food, Agriculture & Environment, Vol.7 (3&4), July-October 2009 861 www.world-food.net Journal of Food, Agriculture & Environment Vol.7 (3&4) : 861-864. 2009 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Estimating saturated and unsaturated hydraulic conductivity and sorptivity coefficient in transient state in sloping lands Majid Raoof 1, 2 , Ali A. Sadraddini 2 , Amir H. Nazemi 2 and Safar Marofi 3 * 1 Faculty of Agriculture, University of Mohaghegh Ardabili, Ardabil Province, Ardabil, Iran. 2 Water Science Engineering Department, Faculty of agriculture, University of Tabriz, Tabriz, Iran. 3 Department of Irrigation and Drainage Engineering, Faculty of Agriculture, Bu-Ali Sina University, Azadegan Boulevard (Charmsazy), Hamadan, 6517833131, Iran. *e-mail:smarofi@yahoo.com, marofi@basu.ac.ir Received 20 May 2009, accepted 4 October 2009. Abstract Double ring and tension infiltrometer are simple and suitable instruments for determining soil hydraulic conductivity and soil sorptivity coefficient. The effect of land slope on soil properties, such as saturated and unsaturated hydraulic conductivity and soil sorptivity coefficient, has been reported by various researchers. The aim of this study was to estimate soil hydraulic conductivity and soil sorptivity coefficient values in lands with different slope gradients, under transient flow conditions. Field experiments were conducted in a loamy soil with different slope gradients in Gonbad Research Station, Hamadan, Iran. Soil surface slope gradients 0 (level), 10, 20, 30 and 40 degrees were selected in this study. For each slope gradient, water infiltration experiments were carried out using a double ring and a tension infiltrometer at tensions of 0, 6, 9 and 15 cm in three replications. Totally 60 water infiltration experiments were carried out. In transient state, Philip’s two-term infiltration equation was applied to determine soil sorptivity coefficient and soil hydraulic conductivity using cumulative infiltration data obtained from the double ring and tension infiltrometer. In this state, the sorptivity coefficient and the hydraulic conductivity for different land slopes and water pressure heads were calculated from Philip’s two-term infiltration equation, which can be obtained by fitting the Philip’s equation to cumulative infiltration data. Results indicated that both the sorptivity coefficient and the hydraulic conductivity values were decreased with increase in tension values. Also the sorptivity coefficient value was increased and the hydraulic conductivity value was decreased with increase in slope gradient. The higher value for decreasing rate of hydraulic conductivity was obtained in lower tensions. With increase of slope gradient from 0 to 40 degrees, decreasing rate of hydraulic conductivity in 0 tension was 3.7 times higher than that in 15 cm tension. With increase in slope gradient the higher value for increasing rate of sorptivity coefficient was obtained in lower tensions. Key words: Saturated and unsaturated hydraulic conductivity, sorptivity coefficient, double ring and tension infiltrometer, transient state. Introduction Hydraulic conductivity is one of the most important hydraulic properties, which affect water flow and solute transport in saturated and unsaturated soils. Also, sorptivity is the basic hydraulic property relating to the square root of time in Philip two-term infiltration equation. In many parts of the world, most of lands are sloping. Most of precipitation and snowmelt water take place in sloping lands. Several researchers have reported that land slope influences soil properties such as moisture distribution, infiltration rate, cumulative infiltration, sorptivity coefficient and saturated and unsaturated hydraulic conductivity 3, 13, 14, 23 . Few measurement techniques and instruments exist for determining soil hydraulic properties and sorptivity coefficient in sloping lands 3, 18 . These include the use of excavated trenches 7 , excavated trenches along the contour line 10 , tracers, piezometers, tensiometers and suction lysimeters 16 and hillslope infiltrometer 9 . Under field conditions, these methods are time consuming, laborious and destructive, also hillslope infiltrometer instrument is not produced in commercial scale 3 . Double ring infiltrometer 4 and tension infiltrometer 11 are simple, fast, convenient and useful instruments for determining soil hydraulic properties based on in situ infiltration experiments. Double ring infiltrometers have been widely used for estimation of saturated hydraulic conductivity under ponding conditions 4 . Also, tension infiltrometers have been proven useful for characterizing unsaturated hydraulic conductivity 2, 15, 21 , sorptivity coefficient 23 , mobile and immobile water content 1 and water conducting porosity 6, 20 . Water infiltration from a tension infiltrometer placed at a sloping landscape can be simulated with various disk diameters, water pressures applied at the soil surface and sloping degrees. The saturated and unsaturated hydraulic conductivity in steady and transient states can be estimated using cumulative infiltration, which is measured by double ring and tension infiltrometer. In transient flow, the amount of water flowing through the voids of soil changes and the infiltration rate reduces with time. In this state, Philip’s two-term infiltration equation can be used to determine the sorptivity coefficient and the hydraulic conductivity by taking advantage of cumulative infiltration data obtained from double ring and tension infiltrometer. This equation has been defined as 12 (1) where I is the cumulative infiltration [L], and C 2 [LT -1 ] are empirical parameters and t is the time [T]. C 1 and C 2 can be related to sorptivity coefficient and soil hydraulic conductivity 23 :