<p>The increasing scarcity of organic resources is becoming a major problem in agriculture in the Mediterranean regions. Searching alternatives has thus become necessary. This study uses Rock-Eval pyrolysis and spectroscopic analysis to test the efficiency of exogenous organic matters (EOMs), such as compost, manure and peat, to improve the soil organic carbon (SOC) content and soil organic matter (SOM) quality in natural soil field plots in the southeast of Tunisia. Spectroscopic (Fourier infrared (FTIR), ultraviolet‒visible (UV‒Vis)) investigations and Rock-Eval pyrolysis standard parameters, were used to assess quantitative and qualitative changes of SOM under EOMs inputs during a test period of 90 days. Thus, the Rock-Eval pyrolysis results revealed that, compared with the other EOMs, the compost presented higher total organic carbon (TOC) and oxygen contents. UV–visible results showed that the input of organic amendments enriched the soil with humic substances rich in aromatic structures and had a high degree of polymerization and polycondensation with more advanced structures. Infrared spectroscopy results showed that EOM inputs, especially those from compost, enhanced aromatic features due to the humification process. EOM inputs are thus an efficient way to improve SOC storage and SOM humification by supplying highly humified organic carbon restitution.</p> Graphical abstract <p></p>