Spatial Variation of some Soil Physico-Chemical Properties of an Alfisol in Southwestern Nigeria

An analysis of spatial patterns of soil properties is important for efficient soil sampling, prediction of soil properties at unsampled sites and developing site-specific farming practices. Spatial variation of soil acidity (pH in water), soil organic carbon (C), total nitrogen, available P, exchangeable K, Mg and clay content were evaluated for some soils under fallow at Ajibode, southwestern Nigeria. The spatial distribution patterns of these soil properties, the range of spatial correlation from semivariance analyses, as well as the required sampling density for fertilizer recommendations were examined. The soil properties exhibit different patterns of statistical distribution. Available P, Mg and K were positively skewed while pH, C, and clay were near normal for 0 – 15 cm soil depth. At a soil depth of 30 – 60 cm, available P was skewed and kurtotic while Mg was skewed. Clay distribution was near normal irrespective of soil depth. Spatial analysis indicated that C, pH, Mg, Clay, Total N and K (for 0 – 15 cm soil depth) and pH, available P, C, Mg and Ca (30 – 60 cm soil depth) are related (spatial dependence) within a distance of 30 – 60 cm. The spatial dependence of the properties studied was weak to moderate. Sampling spacing of 30 – 60 m is appropriate for soil fertility assessment in the test area. A sample size of 37 core samples per hectare is required to adequately predict the mean of soil properties with 5 % allowable error. Keywords: Spatial variability, Soil properties, Semivariogram, Southwestern Nigeria. Nigerian Journal of Soil and Environmental Research Vol. 7 2007: pp. 82-91