Factors Affecting Runoff in Dry Farming Lands of Semi-arid Region in North West of Iran

Water has a vital role in increasing crop yield in dry farming lands in semi-arid regions. This study was conducted to determine factors affecting runoff and develop an equation for predicting the runoff in the dry farming lands. The study was conducted in the Hashtroud, located in south part of East-Azarbijan province in northwestern Iran, from March 2005 to March 2006. A square network of dry farming lands with 900 km2 area was selected and divided into 36 regular grids with a dimension of 5 km. In each grid, runoff plots with dimensions of 22.1 m in length and 1.83 m in width at three replicates and 1.2 m spacing were prepared on a dry farming land with a slope 9%. At the lower parts of the plots, runoff-collecting equipments were established. Rainfall properties were determined on the basis of recording rain gauge data of a meteorological station. Based on results the runoff in the plots was affected by 23 natural rainfall events during the study period. The soils of the study area are mainly clay loam with a moderate infiltration rate and having almost 1% organic materials and 13% lime. Runoff amount per rainfall event varied frame 2.153 to 49.377 liter per plot. Runoff negatively correlated (r= -0.85, p<0.001) with soil infiltration. The results indicated that the runoff can be easily predicted using a linear regression equation based on coarse sand, organic matter and lime (R= -0.84, p<0.001). Coarse sand, organic matter and lime significantly increased soil infiltration and consequently reduced runoff.