The lingering problem of scarcity and high cost of synthetic fertilizers in Nigeria, following changes in Government policies on subsidy, procurement and distribution of inorganic fertilizers, has made inorganic fertilizers unaffordable by the resource – poor farmers, who, incidentally, are the chief food producers in Nigeria. Therefore, the need arises to critically evaluate the potential of certain organic wastes in maintaining and improving soil fertility and crop productivity. To partly meet this need, hence, this paper reports the results of a two – year trial, aimed at evaluating efficacy of different nutrient sources in improving fertility of an Alfisol and performance of cassava (Manihot esculenta Crantz).The experiment was laid out in a randomized complete block design with three replicates. The different sources of plant nutrients included: Poultry manure (PM); wood ash (WA); sawdust (SD); NPK (15 – 15 – 15); and control or check (C)). PM, WA and SD were applied at the rates of 10, 12, and 14 t ha-1, respectively. The results obtained indicated existence of significant (P = 0.05) differences among sources of plant nutrients with respect to their effects on nutrient status of an Alfisol and cassava root yield. At the end of 2011 cropping season, sources of plant nutrients resulted in significant increases in soil organic carbon (SOC) from 0.13 g kg-1 for C to 0.63, 0.55, 0.49 and 0.22 g kg-1 for PM, WA, SD and NPK, respectively. Similarly, at the end of 2012 cropping season, nutrient sources significantly increased SOC from 0.05 g kg-1 for C to 0.69, 0.62, 0.57 and 0.18 g kg-1 for the respective PM, WA, SD, and NPK. At the end of 2011 cropping season, nutrient sources significantly increased total N from 0.22 g kg-1 for C to 0.74, 0.60, 0.67 and 0.52 g kg-1 for PM, WA, SD and NPK, respectively. At the end of 2012 cropping season, nutrient sources significantly increased total N from 0.11 g kg-1 for C to 0.83, 0.68, 0.73 and 0.45 g kg-1 for PM, WA, SD and NPK, respectively. Mean values of cassava root yield data across the two years of experimentation indicated that, nutrient sources significantly increased cassava root yield from 4.18 t ha-1 for C to 8.91, 7.70, 7.00 and 5.46 t ha-1 for PM, WA, SD and NPK, respectively.