Although organic resource quality and quantity are thought to be a modifier of soil organic matter in maintaining soil function and plant productivity, few studies have documented the effect of different organic resource quality and quantity in maintaining soil function and plant productivity in agroecosystems. The main purpose of this experiment was to examine the influence of organic resource quality (as a function of N, polyphenol and lignin contents) and organic resource quantity on crop productivity and carbon storage. Four plant materials Crotalaria juncea, Leucaena leucocephala, maize stover,and sawdust (from Afzelia africana) were selected to represent respectively, Class I, Class II , Class III and Class IV organic resources based on Decision Support System (DSS) of organic resource management. Cattle manure which does not fall into any category of the DSS was also selected as a treatment. A control where no organic resource was applied was included in the treatments. The organic resources were applied at two application rates; 1.2 t C/ha and 4 t C/ha. The experimental design was a split –split plot design with three replicates. An improved maize variety, mamaba was the test crop. The experiment was conducted on two soils of contrasting physical and chemical properties. Soil carbon declined with cultivation irrespective of the organic resource quality and quantity and also with soil type. The decline was however, slower at higher application rates compared to lower application rates at both soils. The field observations show that although plant material is incorporated to soil in large quantities, soil carbon content does not necessarily increase. These results suggest a negative relation between C input and soil C concentration. On the basis of our findings, we hypothesize that organic resource quality and quantity in the short term may not contribute significantly to carbon storage but could have significant effect in increasing maize grain yield.