Effects of Organic Substrate Amendments on Selected Organic Fractions and Biochemical Parameters under Different Soils.

The application of organic substrates can affect soil respiration, dehydrogenase (DH-ase) activity, dissolved organic carbon (DOC), and humic acid (HA) fractions. This study aimed to evaluate the effects of five 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 filter cake compost, (3) biogas sludge-rice straw compost, (4) vermicompost, and (5) sludge. The results showed that soil respiration and DH-ase activity increased rapidly within the first 5 days of incubation, while the concentrations of DOC and HA decreased throughout the incubation period. The highest respiration and DH-ase activity occurred after the application of vermicompost. DOC was found to be the highest in soils amended with sugarcane. The highest concentration of HA was observed with the application of sugarcane residues, regardless of the type of soil. The 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. The 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.