Leaching and associated low soil fertility are among the most important agricultural problems of coarse-textured soils of the humid tropics. This study assessed the effects of synthetic lime and manure-fertilizer combination on soil physicochemical fertility of sandyloam Ultisols in southeastern Nigeria after growing high-density coverage sweet potato in successive rainy and dry seasons. Treatments were application of CaO-88% at 10 t·ha-1 (limed) and 0 t·ha-1 (no-lime) in the rainy season, each with poultry droppings at 20 t·ha-1 (PD20), NPK 15-15-15 at 0.40 t·ha-1 (NPK0.40), complementary manure-NPK at half doses (PD10+NPK0.20) and no-fertilizer in the two seasons. Soil bulk density was unaffected. Soil pH was highest in limed/fertilizer-amended plots (7.1-7.2) and lowest in the control plots (5.6). Liming enhanced soil organic matter (SOM) in the dry season. In both cropping seasons, soil available P was higher in PD20 and PD10+NPK0.20 (36-56 mg·kg-1) than NPK0.40 and nofertilizer (7-11 56 mg·kg-1), while Ca2+ was highest in limed/PD20 (3.59-5.09 cmol·kg-1) and lowest in no-lime/PD10+NPK0.20 (0.89 cmol·kg-1) both of which were among treatments that affected Mg2+ similarly. Apparent cation exchange capacity (CEC) was highest in the control. Overall, liming enhanced soil pH and SOM, manuring enhanced available P, while their combination enhanced Ca2+ and/or Mg2+. The data support adoption of synthetic liming and poultry-droppings manuring for improving SOM and P-availability, respectively, or both practices for raising soil pH toward enhanced cations exchangeability under cover crops in humid tropical environments. This treatment-induced influence of soil pH mostly on Ca2+ but also CEC could be undermined by excessive environmental humidity.