EN
Recently, the use of organic amendments other than traditional manure showed to be efficient for the improvement and/or restoration of soil organic matter in soil. Organic matter from brown coal added to soil may be transformed into humic substances (HS) in (micro)biological and abiotic ways. An application of organic matter from brown coal resulted after 11 years in changed structure of humic acids (HAs) extracted from soil. Despite an increase of the carbon content in the elemental composition of HAs, decreased values of the H:C ratio were due to simultaneous increase of the hydrogen content. HAs extracted from amended soil showed higher absorbance values in the UV-VIS region, higher contents of oxygen functional groups, and were more resistant to thermal decomposition. HAs molecules were also richer in aromatic structures which are relatively resistant to decomposition. Organic matter from brown coal introduced to soil relatively slowly undergoes transformation and thus may cause permanent soil enrichment with HS.