Landscape Controls Physicochemical Properties And Nutrient Dynamics Of A Biotite-Granite Catena In The Rainforest Zone Of Ghana

Abstract

Soil properties and their interactions serve as essential indicators of soil formation and ecosystem sustainability. However, in tropical ecosystems, limited knowledge exists on nutrient dynamics along toposequences and soil depth under varying land-use. Understanding these spatial and vertical variations is critical for developing sustainable land management practices. Field investigations along a biotite-granite toposequence in Ghana's tropical rainforest were used to assess vertical distributions and interactions of soil physicochemical properties across different landscape positions and land-use systems. Structural equation modeling (SEM) was applied to examine relationships among soil properties and land use. Soils showed marked variability along the top osequence and with depth. Surface layers had sandy loam textures, transitioning to sandy clay loam in subsurface horizons. Bulk density was higher in cultivated soils (1.5 g cm 1 ) than in forest soils (1.46 g cm 1 ), reflecting compaction from agricultural activities. Forest soils retained greater soil organic carbon (SOC) and moisture. Soil pH ranged from acidic (5.4) in upper horizons to very strongly acidic (4.6) in deeper layers. Total nitrogen and phosphorus were concentrated in surface horizons, whereas micronutrients, particularly zinc (< 0.5 mg kg 1 ), were deficient. SEM indicated significantly lower C:N:P ratios in croplands due to SOC depletion and nutrient imbalance. The study demonstrates that forested landscapes enhance SOC, nutrient availability, and soil health compared to cultivated systems. These findings underscore the importance of conserving natural vegetation and integrating landscape position in designing sustainable soil and nutrient management strategies for tropical agroecosystems.