Changes in humic fraction characteristics and humus-enzyme complexes formation in semiarid degraded soils restored with fresh and composted urban wastes. A 5-year field experiment

• Published in: Journal of soils and sediments 2018-04, Vol.18 (4), p.1376-1388
• Main Authors: Lucas, Encarnación García, Izquierdo, Carlos García, Fernández, Mª Teresa Hernández
• Format: Article
• Language: English
• Subjects: Absorption; Acidic soils; Aliphatic compounds; Banded structure; Bioremediation; Capacity; Carbon 13; Carbonyl compounds; Carbonyls; Composting; Composts; Control; Decomposing organic matter; Earth and Environmental Science; Environment; Environmental Physics; Enzymes; Extracellular; Extracellular enzymes; Fourier transforms; Function and Fate in the Environment; H alpha line; Household wastes; Humic acids; Humic substances; Humus; Immobilization; Immobilized enzymes; Infrared spectroscopy; Microorganisms; Natural Organic Matter: Chemistry; NMR; Nuclear magnetic resonance; Organic carbon; Oxygen content; Polysaccharides; Restoration; Sewage; Sewage sludge; Sludge; Soil; Soil amendment; Soil conditions; Soil degradation; Soil improvement; Soil quality; Soil Science & Conservation; Spectra
• ISSN: 1439-0108; 1614-7480
• DOI: 10.1007/s11368-016-1537-8

Purpose The aim of this study was to evaluate in the medium term (5 years) the effect of two organic amendments, which were spiked to a degraded soil as a strategy for bioremediation, on the amount and characteristics of soil humic acids (HAs) and their ability to associate with certain extracellular enzymes. Materials and methods Soil samples were collected in an experimental field where 5 years earlier, a mixture of the organic fraction of household waste and sewage sludge (2:1 ratio), both composted (composted residue, CR) and non-composted (fresh residue, FR), had been added in triplicate at rates equivalent to 1 % (D1) and 3 % of organic carbon (D2) to 30-m 2 plots as a strategy for degraded soil restoration. Humic substances (HSs) and HAs were extracted from the collected soil samples and submitted to chemical, biochemical, spectroscopic (FTIR), and chemical-structural (CPMAS 13 C NMR) analyses. Results and discussion After 5 years, the amended soils showed significantly higher HS and HA content than did the control soil, and the differences with respect to the control were greater with compost addition than with FR addition. The HA from the amended soils had higher H, N, and S contents than the HA from the non-amended soil in addition to a lower oxygen content and lower O/C ratio values. Furthermore, the FTIR spectra of the HA from the amended soils showed a higher absorption intensity in bands corresponding to aliphatic and amide-carboxylic groups and polysaccharide structures and a lower absorption intensity in bands corresponding to carbonyls and carboxylic groups than the HA from the control. These results were confirmed by 13 C-NMR spectra, which showed a clear increase of aliphatic compounds in the HA from the amended soils with respect to the HA from the control. HA spectra were not greatly influenced by the maturity of the amendment or by the application dose. Conclusions In general, the addition of organic amendments increased the quantity of enzymes immobilized in the humic colloid. Furthermore, the addition of the composted residues favored to a greater extent the immobilization of the abovementioned enzymes, which represent a biological reservoir in the soil. This is of great importance since these enzymes possess functional capacity even when the soils are under conditions that are stressful or unfavorable for microbial life. An increase in the quantity of immobilized enzymes such as that observed in amended soils supposes an important