An assessment of the variation in soil properties within and between landform in the Amol region, Iran

Soil survey users require statistically valid information on the distribution and variability of soil attributes that are important for management and land use. Rigorous investigations of soil property distributions are rare, and statistical methodologies for soil survey applications are not commonly utilised. The objectives of our research were to: (i) evaluate the statistical distribution of soil properties for several landform elements, (ii) interpret these distributions in terms of pedogenic and other processes. Eight soil properties were measured for 57 pedons on 4 landform elements in the Amol region of Iran. Landforms were piedmont plain, levee, behind levee and lowland. The selection of samples was on the basis of distinct layers present in profiles. Clay concentration has a normal distribution for the soil samples from each of the four landforms whereas silt concentration is normally distributed only for the piedmont plain, CaCO3 for lowland and CEC except for lowland. Concentrations of sand and organic carbon (for all landforms), EC (except for behind levee), CaCO3 (except for levee) and CEC (lowland) followed lognormal distributions. However there were some soil properties for which a log transformation did not produce a normal frequency distribution. Care should be taken when applying statistical tests that are sensitive to departures from normality but asymmetric or misshapen distributions may still provide meaningful information. In order to investigate the distribution patterns of soil properties for the different landforms, factor analysis was performed on the data for each soil layer and this strongly differentiated the landforms. For the piedmont plain, attributes reflecting illuviation of clay dominate whereas for levee and behind levee soils original properties of stratified sediments are the dominant factors. For the lowland, variations in the factors indicate that pedogenic processes rather than sedimentary layering are dominant. The important contributions of both sedimentary sorting and pedogenesis to the distribution and properties of soils have been revealed by statistical analysis.