Application of GIS in the Study of Spatial Variability of Selected Soil Properties in Southeastern Nigeria

Assessment of spatial variability of soil is a key component to sustainable food production. Soil sampling is being threaten by the insecurity ravaging the African nations. The combination of both the conventional analytical method and geostatistical method were used to analyse the variability of some soil properties in three state of the Southeastern Nigeria. A total of 18 profile pits were dug and sampled on soils underlain by six different parent materials. The sand content, clay content, porosity, pH, organic carbon (OC), available phosphorus (AP), base saturation (BS) and effective cation exchangeable capacity (ECEC) were analysed using standard analytical procedures. The study reveal that sand content predominate other soil properties with highest value of 87.7%. The clay content varied and falls within the range of 9.31 – 3.45%. The total porosity was more than 40% in all the soils studied. The pH ranged from 5.47 – 7.14, the OC ranged from 3.9 – 11.7g/kg, the AP ranged from 7.21 – 12.45mg/kg, the BS ranged from 37.75- 89.13% and the ECEC ranged from 4.03 – 11.23cmol/kg. The result of the geostatistical analyses revealed that spatial dependence (SD) below 25% indicating strong SD was observed in porosity, organic carbon, phosphorus and ECEC. Moderate SD was observed in in sand content, clay content and pH while weak SD was observed in the percentage base saturation. The SD was apparent in 13873 -79156.76m ranges. The coefficient of determination (R2) of clay content and ECEC were greater than 0.5 indicating a good fit. The Root Mean Standardized Error (RMSE) <1 was observed in pH and ECEC indicating good prediction of the measured value. This study suggest that OK interpolation method can be used to predict spatial distribution of some soil properties at large scale with few sampling points. Keywords: spatial variability, soil properties, spatial dependency, ordinary kriging.