Soil structure is essential for sustained provision of ecosystem services such as water filtering and storage, waste disposal, carbon sequestration and many more. Structural degradation/disaggregation of soils emanating from human activities such as mining, grading and filling interferes with the ability of soils to perform these functions. The present study examines the roles of clay mineralogy, native organic matter, and exogenous organic material on the restoration of structurally degraded soils. Totally seven soils from Denmark and Ghana - five soils dominated by illites, one kaolinitic soil, and one smectitic soil were sieved to 2 mm, and half of each soil amended with ground rape, packed in lysimeters, and incubated in the field for 20 months to monitor structure regeneration. During and after the incubation period, soil structure indicators and microbial activity were assessed. During the incubation period, structural stability estimated as the amount of water-dispersible clay decreased with prevailing moisture content, and native organic matter. Also, microbial activity significantly increased with addition of exogenous organic matter. At the end of incubation, there was significant macroaggregation, decreased bulk density, and increased equivalent pore diameter and tortuosity (derived from measurements of soil-gas diffusivity and soil-air permeability) for all soils. Although aggregate friability was not affected by clay type, aggregate workability was highest for the kaolinitic soil and lowest for the smectitic soil. Among the illitic soils, aggregate workability increased with native organic matter content. Addition of exogenous organic material showed little effect on soil physical properties. Results points to the possibility of regenerating the structure of physically degraded soils by exposure to natural climate cycles together with organic amendment.
Main Research Area:
Soil Systems and Critical Zone Processes - Integrating Life Support Functions across Disciplines, 2013