Aim of the study:
The rapid conversion of tropical secondary forests into intensive agriculture threatens soil hydrological functions, yet empirical data within Wallacea’s watersheds remain scarce. This study investigates the impact of land-use changes on soil hydraulic architecture and infiltration capacity within the Wimbi Sub-watershed, Central Sulawesi, Indonesia, providing a scientific foundation for regional watershed preservation.

Material and methods:
In situ soil infiltration was measured via stratified purposive sampling (n=15 per land use, total 45 points) using a double ring infiltrometer across secondary forest, agroforestry, and cultivated land (maize monoculture). Core physical properties, hydrodynamics, and soil organic carbon (SOC) were quantified via standardized laboratory protocols. High-resolution infiltration data were calibrated using the Horton model solved via an iterative non-linear least-squares regression framework.

Results and conclusions:
Forest conversion to intensive agriculture causes significant degradation of soil hydraulic properties. Secondary forest exhibited the highest steady-state infiltration capacity (7.74±0.45 cm⋅h−1), followed closely by agroforestry (6.94±0.38 cm⋅h−1), both categorized as moderately rapid. Conversely, cultivated land showed a 50% decline to 3.87±0.21 cm⋅h−1 (moderate). Non-linear fitting demonstrated that the Horton model effectively captures infiltration dynamics (R2≥0.89). This agricultural restriction was directly associated with mechanical compaction, which increased bulk density (1.61±0.07 g⋅cm−3) and depleted total porosity (33.18±1.45%). The critical deficit in SOC (0.98±0.08%) on cultivated land is highly indicative of accelerated surface sealing, which potentially restricts subsurface internal pore networks. Conversely, agroforestry sustained superior soil structural buffering through elevated SOC (4.20±0.31%), which mitigated matrix compaction and enhanced pore connectivity. Transitioning to tree-based farming is essential to mitigate runoff and restore tropical watershed resilience.