Spatial variation of soil physical properties in adjacent alluvial and colluvial soils under Ustic moisture regime

Abstract. Soils vary spatially due to differences in soil management and soil formation factors. The soil spatial variability is an important determinant of efficiency of farm inputs and yield. This study was carried out to identify and compare spatial variation of some soil physical properties by geostatistics in alluvial and adjacent colluvial soils formed under ustic moisture regime at Gökhöyük State Farm (1750 ha), Amasya, Turkey. Seventy four soil samples were collected on a regular grid (500 × 500-m) and additional 224 samples were collected on 28 500-m fine-transects, randomly superimposed between the nodes of grids. Semivariograms and corresponding kriging maps for soil texture, soil organic matter (SOM), bulk density (BD), saturated hydraulic conductivity (K_s), and available water content (AWC) were prepared. Statistical analyses were conducted separately for colluvial and alluvial sites as well as whole area. The soils in alluvial site is rich in clay with high BD and SOM, and low in K_s and AWC; and the soils in colluvial site was designated as low in K_s, SOM, and AWC and high in BD. All variables, except SOM, showed a strong spatial dependency. In general, nugget, sill and range values of most of the studied soil variables decreased from alluvial site to colluvial site. When local (alluvial and colluvial sites separately) and global (alluvial + colluvial) kriged maps for BD, AWC, and soil textural separates, use of global semivariograms (one semivariogram for entire study area) resulted in lost of some details in colluvial sites, suggesting that local semivariograms for alluvial and colluvial soils should be used in kriging predictions at the farm. The results had significant implications for water management as AWC was spatially associated to clay content in alluvial site and to clay and sand contents in colluvial site.