| Autor: |
Dultz, S., Schellhorn, M., Schmilewski, G., Schenk, M., Dombrowski, I., Schmidt, E., Walsch, J., Below, M. |
| Jazyk: |
angličtina |
| Rok vydání: |
2010 |
| Zdroj: |
GEOTECHNOLOGIEN Science Report |
| DOI: |
10.2312/gfz.gt.16.10 |
| Popis: |
The addition of clay to growing media aims at constant supply of potassium, phosphorus and micro nutrients, pH-buffering, improvement of rewettability, and cohesion of growing media. The identification of suitable clays and their classification is a prerequisite for product and cultivation safety. A range of different clays highly variable in their mineral parameters were selected for experiments on nutrient buffering (P) and Mn toxicity, their ability to improve the rewettability and binding capacity of growing media. From batch experiments and growth trials it was derived that a threshold value for the sum of exchangeable and easy reducible Mn in clays for growing media is not justified, as even very high Mn contents in clay were not phytotoxic. The P binding capacity of clays was strongly correlated with the oxalate extractable Fe and Al content. A newly developed capillary rise method (WOK) was used to characterize the rewettability of growing media. The speed of rewetting mainly depends on the fineness of the amended clay. Surface free energy (SFE) data of the growing media indicate that those with a good rewettability show also high values for SFE. Compared to the kaolinitic and illitic clay amendments, bentonites show no significant increase in the SFE. Surfaces of clay minerals exhibiting originally polar and hydrophilic surfaces, can render hydrophobic when coated with weakly or non-polar organic matter moieties. Dissolved organic carbon (DOC) sorption was found to be positively correlated with the specific surface area (SSA), cation exchange capacity (CEC) and amount of dithionite extractable Al and Fe. Clays containing expandable clay minerals with high CEC and SSA (e.g. smectites) and those rich in Al- and Fe-oxides seem to be less effective for improving rewettability, whereas an addition of non-expandable clays with lower SSA, CEC (e. g. kaolinitic and illitic clays) and amorphous oxide content appears more promising. New insights on the adsorption of DOM on clay mineral`s surfaces will be obtained in the third year by chemical analysis of the surface with X- ray photoelectron spectroscopy (XPS), surface topography analysis and contact angle measurements. A new method for the determination of the binding capacity of clays in blocking media is currently being tested and will be studied together with determinations on K-dynamics. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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