R. TalaeiA, A. Jafari ArdakaniB , F. AzimiA, R. BayatB and M. ParehkarB A Scientific Member of the Center of Agriculture and Natural Resources of Ardabil, Ardabi. Email: rztala@yahoo.com BScientific Members of the Center of Soil Conservation and Watershed Management, Tehran

Manuscript Accepted: 24/04/2010

Manuscript Received: 01/01/2011

:Abstract

One of the main resonator factors in watershed soil erosion is inappropriate land management including conversion of pasture land to dry-land farming. Unfortunately, the changes of Gara Su watershed usages have been very common. Thus, in order to understand the influence of land use on runoff rate and soil loss, soil losses were investigated and determined under both pasture and dry-land agricultures at sub-watershed of Dojag chay in southern west Qara Su Basin (within Ardebil province). In this Research, using a drop maker rainfall simulator device, 18 treatments under the said watershed were conducted using an artificial rain with the intensity of 6 mm/ min for 6 minutes and soil loss rate was measured due to the rainfall in two user types in dry-land and rangeland under natural humidity conditions and approximately the same as the raining season in three slope classes of 5 to 12, 12 to 20 and greater than 20. The results showed that with the cultivation, cultivated soils get empty and their porosity and permeability increase so, with the increase of water penetration ability, their runoff compared to the pasture lands starts with delay. Comparing the amount of runoff shows that after runoff gets started in rain-fed agriculture lands, the flowing speed and amount of water become more than those of pasture lands and the statistical analysis also verified the significant relationship, especially in slopes of more than 20% between the amount of soil loss and land use. The soil loss under rain-fed agriculture was 8.8 times more than the pasture. As the soil loss was compared for different slope classes of 5-12, 12-20, and more than 20 slope percent, the results indicated that the soil losses under rain-fed agriculture were 4.5, 5.6, and 12 times more than the pasture. The study results, therefore, can be utilized for proper management of area through devoting necessary attention into land uses.

Keywords: Pasture land, dry-land farming, Soil loss, Dojag Chay watershed, Rainfall simulator and Runoff