CHEMICAL-CHANGES IN HUMIC SUBSTANCES FROM COMPOST DUE TO INCUBATION WITH LIGNO-CELLULOLYTIC MICROORGANISMS AND EFFECTS ON LETTUCE GROWTH

Differences in the chemical properties of the organic matter from a hi ghly lignocellulosic compost after incubation with two ligno- and cell ulolytic microorganisms were studied in this work. Inoculation with ei ther of the two microorganisms assayed, Trichoderma viride or Bacillus sp., of soil-compost mixtures enhanced degradation processes and the degree of organic matter humification. According to the humification i ndex, inoculation with T. viride produced the highest humification rat e in all the compost-soil proportions studied (10, 20 and 30%). To eva luate the quality of the extracted humic substances according to their electrofocusing behaviours a new index was established. This index sh owed an increased yield of humic substances of the lowest electrophore tic mobility (highest molecular weight) in treatments inoculated with Bacillus sp., whereas inoculation with T. viride enhanced the formatio n of molecules of the fastest electrophoretic mobility. These results, together with the fibre analysis performed, showed that the nature of the humic substances produced after incubation appeared to depend gre atly on the degradation pathway carried out by the inoculated microorg anism, T. viride or Bacillus sp.. Both degradation-humification pathwa ys beneficially affected lettuce growth, demonstrating that inoculatio n with any of these two microorganisms may be a useful tool to modify agronomic properties of unripe composts.