Background and aims Grassland management practices alter plant litter input into soil in terms of quantity and quality via defoliation, nutrient input and trampling. These alterations may impact litter decomposition and soil organic matter (SOM) quality and quantity. Here, we aimed to investigate the effect of four grassland management practices (unmanaged, low and high intensity grazing, and mowing) on organic matter (OM) input quality and its relation with SOM composition. Methods We considered three types of OM input: aboveground and belowground material from living plants and partly degraded aboveground litter. We assessed their quality based on their elemental (C and N) contents, their stable carbon isotope (C-13) and their lignin composition. Results The results showed that C/N ratios differed among plant-derived OM input types but did not vary among treatments. In contrast, lignin biogeochemistry and lignin/N ratios of plant tissues were differentiated according to input type and treatment. High grazing intensity resulted in the lowest lignin/N ratios of aboveground litter. Lignin chemistry of all plant OM input types under grazing treatments indicated low maturity stage. Despite the similar lignin contribution to soil carbon under all grassland management practices, soil lignin was more degraded under mowing than under the other practices. Conclusions We conclude that grassland management may have an impact on SOM composition by altering plant OM input composition rather than its stoichiometry.