Soil erosion is a major constraint to agricultural productivity and environmental sustainability in humid
tropics. However, the effectiveness of organic amendments in controlling runoff and sediment losses in soils of different
geologic origins remains poorly understood. This study evaluated the effects of selected organic amendments on surface runoff and sediment yield under controlled laboratory conditions by using soils derived from four geologic formations:Asu River Group, Bende Ameki Group, Coastal Plain Sand, and False-Bedded Sandstone. Four types of organic amendments (poultry droppings, goat droppings, municipal solid waste, and a combination of amendment) were applied at different rates (10, 20, and 30 t ha−1) to 10 kg of soil in a completely randomized design. After a 3-month incubation period, rainfall simulations were conducted under both air-dry and wet soil conditions representative of contrasting antecedent moisture states commonly observed in the area. Data were then analyzed through an analysis of variance,and treatment means were separated using least significance difference at a 5% probability level. The results indicated that increasing the amendment rates significantly reduced surface runoff and sediment yield across all soils, although the magnitude of response varied with geologic formation and moisture. Poultry droppings and combined amendments at 30 t ha−1 consistently produced the greatest erosion reductions, particularly under air-dry conditions. A negative correlation was observed between clay content and sediment yield (r = −0.32 and −0.21) in both moisture states, which highlights the role of soil texture in erosion resistance after amendment. In summary, this study demonstrates that organic amendments, especially poultry droppings and combined treatments, are effective in mitigating erosive losses and reducing the potential for sediment-bound nutrient transport. These findings underscore the value of amendment as a practical soil and water conservation strategy for minimizing sediment yield and supporting sustainable land practices in erosion-prone tropical environments.
Key Words: organic amendment, rainfall simulation, sediment yield, soil degradation, soil erosion, surface runoff