Conjugation of artificial humic acids with inorganic soil matter to restore land for improved conservation of water and nutrients

Artificial soil (AS) with a dark–brown appearance and high soil organic matter (SOM) was manufactured under hydrothermal conditions from poor sandy landfill using the 'hydrothermal humification process.' This approach may retrosynthesize the natural clay–humin complex, which is the main contributor for water and ion binding in fertile, natural soils. The structure and morphology of as-created organic–inorganic composites was examined, and it was shown that the as-created artificial SOM (A-SOM) indeed tightly binds to the mineral surfaces, thus creating remediated soil or more general AS. A-SOM does not change the bulk structure of the involved inorganic minerals but activates their surface. Depending on the biomass used as the starting product, the high effectivity of synthetic humification improves the organic carbon and nitrogen content when compared with the employed sandy soil (SS). The composition was adjusted to be comparable with a reference sample of cultivated soil (2.92% in C content and 7.8% in SOM) to enable a fair referencing. We then analyzed the most frequently used soil quality indicators for agricultural land use and found strong water retention and nutrient conservation, which reflects the successful restoration of mineral–humus conjugation. Pure ASs provide superior performance in the analyzed series, whereas simulated soils (mixture of SS and AS) still exhibit satisfactory capacities of water and ion bonding. The values were found to be very similar to cultivated soils sampled from Germany and Harbin, China