Spatial variability of soil properties under different land uses in the Koupendri catchment, Benin

The knowledge of the spatial distribution of soil properties such as saturated hydraulic conductivity (Ksat), bulk density (BD), soil organic carbon (SOC), total nitrogen (TN) and available phosphorus (Avail. P) is fundamental to sustainable management of soil resources. A total of 291 surface soil (020 cm) samples were collected across three land use types: maize-sorghum (MS), rice field (Rice) and fallow shrub-grassland (FSG) in Koupendri, north-west Benin using a grid sampling of 25 m x 25 m. Additional soil samplings at 5 m x 5 m was carried out within the sampled area to capture small-scale variability. Data obtained were analysed using classical statistics, including Pearson's product moment correlation and analysis of variance and spatial statistics. The soil properties showed normal and non-normal distributions, and the coefficient of variation was high (75-126.7%) for Ksat, moderate (2945%) for SOC, C/N and Avail. P, and low (7-15) for BD and TN across the different land use types. Land use had a significant (P < 0.05) effect on all the soil properties evaluated except C/N. The highest values of Ksat (151.6 cm/d), SOC (1.26%), BD (1.79 g/cm(3)), TN (0.105%), Avail. P (4.66 ppm) and C/N (12.14) were obtained under the MS cropland whereas porosity was highest (43.7%) in the rice field. Highly significant correlation (P < 0.01) was observed among the soil properties irrespective of land use. The correlation length (65-300 m) and nugget effect ratio indicate high variation and strong spatially dependent soil properties. However, TN, BD, Avail. P and C/N were weakly spatially dependent. The variograms were fitted with mostly exponential and spherical models for mapping the variation in soil properties. The interpolation map could help in delineating different soil fertility and soil water management zones aimed at making good agronomic decisions.