TITLE:
Spatial Variability of Selected Soil Attributes under Agricultural Land Use System in a Mountainous Watershed, Ethiopia
AUTHORS:
Hailu Kendie Addis, Andreas Klik, Stefan Strohmeier
KEYWORDS:
Semivariogram, Soil Attribute, Spatial Variability, Watershed
JOURNAL NAME:
International Journal of Geosciences,
Vol.6 No.6,
June
19,
2015
ABSTRACT: In the Ethiopian
Highlands, research projects were often measuring soil attributes of spatially
structured point data but soil variability at a watershed scale is not clearly
defined. This study was conducted to assess the correlation among selected soil
attributes and to illustrate the spatial pattern and dependence of neighboring
observations. The 53.7 km2study
watershed was divided into a 500 m by 500 m square grid using arcgis and at the
center of each grid soil samples from 0 to 25 cm depth were collected within
184 locations. The descriptive statistics revealed available phosphorous (AP)
had the largest coefficient of variation (CV = 104) while pH was the least
variable. There was a positive link between elevation and SOC whereas bulk
density (ρd) and pH indicated an inverse relationship with elevation and SOC.
The value for nugget/sill of ρd, pH and elevation are less than 0.25, and
depicts that it has strong spatial autocorrelation. The value for nugget/sill of SOC, and TN found between 0.25
and 0.75, and indicate that they have moderate spatialautocorrelation. With regard to AP,
the value for nugget/sill is more than 0.75, which displays a weakspatial autocorrelation.
Semivariograms of ρd, pH and elevation were best fitted to Gaussian model
whereas SOC, TN and AP were best fitted to exponential function. Generally, the
study verified that soil measurements taken at the given scale through regular
sampling interval were adequate to capture the spatial dependence of numerous
initial soil assessments in the study watershed.