Spatial correlation between the composition of the clay fraction and contents of available phosphorus of an Oxisol at hillslope scale

Relief is regarded as the abiotic factor most strongly influencing pedogenic processes at a local scale. The spatial correlations between the composition of the clay fraction (iron — Fe and aluminum — Al oxides, kaolinite and organic matter — OM) and contents of available phosphorus (P) of an Oxisol were evaluated at hillslope scale under sugarcane cultivation. A total of 119 samples were collected at intersection points on a 100 × 100 m georeferenced grid of regularly spaced points 10 m apart in the 0.2–0.4 m depth in an area consisting of two landform components namely: component I (an area with a linear hillslope curvature), and component II (one with a concave–convex hillslope curvature). Soil OM and available P contents were subjected to descriptive statistics and geostatistical analyses in order to assess their variability and spatial dependence. All attributes studied were spatially dependent. Available phosphorus had positive spatial correlation with high crystalline goethite, hematite and gibbsite. Identifying small hillslope curvatures is useful with a view to better understanding their relationships with soil organic matter and available phosphorus, as well as kaolinite and Fe and Al oxide attributes. A simple correlation analysis by itself is inadequate to relate attributes, which requires a supplemental, geostatistical technique.

► Spatial correlations between clay fraction and available P of an Oxisol were evaluated. ► Relief influenced the spatial distribution of Fe and Al oxides and the P available. ► The highly crystalline oxides were positively correlated with soil available P. ► Identifying relief is useful to understand the relationships with P and clay fraction. ► Relief is an effective pedoenvironmental indicator of P availability.