Geostatistical Evaluation of Spatial Variability of Selected Soil Physical Properties under Different Crops in Ado Ekiti, Nigeria

Abstract

The characterization of spatial variability of soil physical and chemical characteristics is very important for precision farming and managing agricultural production. Therefore, the objective of this study was to evaluate the spatial variability of selected physical properties of a soil under different crops in Ado Ekiti, Nigeria using descriptive statistics and geostatistical techniques. Grids of 10 m x 10 m were set up on the field within three land uses. The field was about 3 hectares, out of which 1ha was apportioned for cowpea, 1ha was for sole maize and the rest for maize/cassava intercrop. A total of one hundred and eighty-four (184) georeferenced surface samples were collected for analysis of texture, bulk density (BD), particle density (Pd), porosity (Pt) and saturated hydraulic conductivity (Ks). The study used descriptive statistics to investigate the striking features in each soil property and further adopted semi-variogram and kriged maps to assess the spatial dependence and classification of the soil properties respectively. The soil properties showed varying degrees of spatial variability, with Ks highly variable (118%) than others. There was weak correlation between Ks versus BD (12%) and Pt (-14%) but the correlation was significant with sand content (22%). The mean value of bulk density was 1.43 g cm-3 while the hydraulic conductivity (Ks) was averaged 48.74 cm hr-1. From the variogram, the range values for sand and clay was about 14 m while it was 510 m for bulk density, total porosity and particle density and about 411 m for Ks. The range of spatial dependence values indicated that future sampling could be done within a distance between 14 and 510 m. The semi-variogram revealed sand and clay having strong spatial dependence, Ks having moderate spatial dependence whereas others showed weak spatial dependence structure. The kriged maps further showed the spatial distributions of these soil physical properties across the three different land use systems. As the measured soil physical properties is shown to vary in space and exhibited random spatial patterns, the study suggested that the field could be susceptible to erosion since it is dominated by high bulk density, high sand content, hydraulic conductivity and subsequently low porosity.