This study examined the effects of two organic matter sources of high carbon and low nitrogen (cocoa pod husk) or high nitrogen and low carbon (cattle manure) contents on the chemistry of a volcanic soil under cocoa production in Papua New Guinea (PNG), with a field study including eight treatments: no amendment (control), cocoa pod husk (CPH), cattle manure (CM), NPK, CPH+CM, CPH+NPK, CM+NPK, and CPH+CM+NPK, all replicated five times in five blocks with each treatment applied to five trees in a randomized complete block design, applied in a split manner initially and after two and a half months, with soil samples collected within 50 cm depth at the end of the fifth month using four out of five replicates, treatment averages calculated (n=4) and statistically analyzed using two-way ANOVA to determine significant differences (p0.05), and where interaction between treatments and profile depth was found, one-way ANOVA with Tukey’s HSD and pairwise comparisons was performed, and results showed that CPH and CM alone or combined improved all soil physical and chemical properties, with soil organic matter, organic carbon, organic carbon stock, and macronutrients more influenced by carbon (CPH) than nitrogen (CM), while soil water-holding capacity, moisture, pH, electrical conductivity, and most micronutrients were improved by nitrogen, indicating these relatively inexpensive and readily available organic matter sources in PNG have implications for sustainable soil fertility management under cocoa production to enhance yields for smallholder farmers.