,e application of organic substrates can a0ect soil respiration, dehydrogenase (DH-ase) activity, dissolved organic carbon
(DOC), and humic acid (HA) fractions. ,is study aimed to evaluate the e0ects of 6ve organic substrates in the organic fractions of
degraded alluvial soil, acid sulfate soil, and sandy soils and the physicochemical properties of the soil. Soil samples were amended
at a rate of 5 tons ha−1 with (1) water hyacinth compost, (2) sugarcane 6lter cake compost, (3) biogas sludge-rice straw compost, (4)
vermicompost, and (5) sludge. ,e results showed that soil respiration and DH-ase activity increased rapidly within the 6rst 5 days
of incubation, while the concentrations of DOC and HA decreased throughout the incubation period. ,e highest respiration and
DH-ase activity occurred after the application of vermicompost. DOC was found to be the highest in soils amended with
sugarcane. ,e highest concentration of HA was observed with the application of sugarcane residues, regardless of the type of soil.
,e application of water hyacinth and biogas sludge stimulated cumulative HA only in the acid sulfate soil, while vermicompost
improved HA only in the degraded soil. ,e largest stimulation in respiration and DH-ase activity was observed in degraded and
sandy soils, regardless of the type of amendment. In the acid sulfate soil (3.7 mg·C·g−1), larger amounts of DOC and HA were
observed than in both degraded (1.7 mg·C·g−1) and sandy soils (1 mg·C·g−1). However, DH-ase activity was the lowest in acid
sulfate soil.