Effect of organic manures and chemical fertilizers on maize (cv. DMR-ESR-Yellow) was studied in a degraded upland soil. Four levels (0, 1, 3, and 5 t ha-1) of palm kernel and barley residues and a recommended rate of chemical fertilizers were tested in a randomized complete block design with three replications. Plant height, stem diameter, number of leaves, ear leaf area, 1000 grain weight, and grain yield increased with the increase rate of manures, but the increase was higher in palm kernel than the barley residue. The 3 and 5t ha-1 rates of palm kernel residue were the best treatments due largely to higher supply of N, P, K, Ca and Mg as. Under high rainfall, grain yield increased likely by reducing days to tasseling and silking and anthesis silking interval (ASI). Under low rainfall, both organic manures, which may have maintained more favourable soil moisture and temperature regimes, gave considerably higher yield than the recomended fertilizer rate (NPK 15:15:15). Organic manure treated plants, especially under palm kernel residue with higher N supply reached 50% tasseling and silking earlier and had shorter ASI and longer grain-filling period than inorganic fertilizer. The use of 3 to 5t ha-1 of palm kernel residue manure could substantially increase grain yield in Sierra Leone. However, the increase in yield with application rate showed that the highest rate used was not the optimum. Therefore, higher rates should be included in subsequent trials to obtain maize response curves for both manures.