Organic resources (ORs) are essential inputs in tropical farming systems and their decomposition dynamics are related to their quality. ADecision Support System (DSS) for organicNmanagement has been proposed earlier that subdivides ORs in four classes depending on their N, lignin, and soluble polyphenol contents. To validate this DSS, a 28-d aerobic incubation experiment was initiated with 32 ORs, mostly crop and tree residues, applied to a sandy loam soil. The ORs contained 1.4 to 53.2 g kg?1 kg?1 of N, 25 to 295 g kg?1 ranged from 70 to 820 g kg?1 between 199 and 905 mg CO2–C kg?1 ranged from 5 to 109 mg N kg?1 of lignin, and 4 to 148 g of soluble polyphenols. In vitro dry matter digestibility (IVDMD) . After 28 d, CO2 –C production varied soil, and mineral N contents soil. Based on N mineralization data, three classes of ORs were evident: Class A with N release ? 0, Class B with N release approximately 0, and Class C with N release ? 0 (N immobilization). Criteria to separate those classes were based on the OR N and polyphenol content and cut-off values between the classes agreed well with those proposed in the original DSS. For Class AORs,Nmineralization was negatively related to their lignin/N ratio (except for Gliricida residues) and for ClassCORs,Nimmobilization was positively related to their N content. Short-term mineralization data supported the existence of three classes of ORs instead of four originally proposed by the DSS. However, ORs also govern other functions, operating in the medium to long term, and for these func- tions, the original four-class concept may be proven valid.