Relationships between soil fertility indicators and toposequence in the Sudano Sahelian watershed of Koutango in the southern peanut basin of Senegal

Abstract

With the progressive land degradation, the use of watershed could be an alternative for cropping to achieve food security. By using statistical methods, this study aims to highlight relationships between different soil properties and toposequence in a 173.3 km²-watershed. Stratified soil sampling strategy associated with principal component analysis (PCA) and Chi-square (^÷2) test, have emphasized the variability of soil properties at the watershed scale. Soil physical and chemical properties analysis using standard methods, showed differences for soil organic carbon (OC) at the soil surface at the lowland level (5.51 g kg^-1), terraces (3.34 g kg^-1), colluviums (3.25 g kg^-1), and upland (3.13 g kg^-1). Cation exchange capacity (CEC) in the surface horizon also decreased along the toposequence with 3.36 Cmol kg^-1 in the lowland and 1.93 Cmol kg^-1 in the upland. The same trend was observed at the deep horizon for OC and CEC between the different soil units. PCA showed a correlation of 60%, 64% and 63% for surface, intermediate and deep horizons respectively between soil properties such as OC, CEC and ECEC. ^÷2 test confirmed the influence of the toposequence on almost all soil properties measured, excepted with P in the surface horizons emphasizing the need to include agricultural practices that can influence soil variability.

Keywords: Indicators of soil fertility, toposequence, watershed