Spatial Variations of Surface Soil Physical and Chemical Properties on Different Landforms of Tabriz Plain

The aim of this study was to evaluate the spatial variability and frequency distribution of some physical and chemical properties within and between various landforms ofTabriz plain in the northwest of Iran. For these evaluation 13 properties of 98 surface soil samples according to grid sampling design with 1000 meters interval based on soils variability were selected and analysed. Landforms in the study area included hill، piedmont plain، plain، river alluvial plain and lowland. The study of soil variables frequency distribution showed that Bd، CEC، CCE، pH، clay and silt followed normal distribution، and these variables were used in parametric statistical method. Variables such as MWD، total N، SAR، OC، EC، available P and sand showed log-normal distribution. The variables frequency distribution increased within landforms، in lowland، hill، and river alluvial plain they showed normal distribution. Only EC in piedmont plain and sand، OC and total N in plain landforms land forms showed log-normal distributions. Results indicated significant differences in soil properties distribution among landforms. Clay، pH، EC، SAR and MWD، CEC، Bd، total N، OC، available P، sand، and silt were strongly and moderately spatial dependent، respectively، while CCE had no spatial dependence and it followed nugget model. These results indicated strong spatial dependence due to the effect of intrinsic factors such as parent material، relief and soil types. Also soil properties variations could result from variation in depositional environments and/or differences in pedogenic or hydrologic processes for different landforms. These environmental factors can be affected by flood water، irrigation، fertilizeir addition، high water table level or agriculture practices. They may affect data deviation from normal distribution and cause skewness (positive or negative) at soil mapping unit.