Project properties
Title The effect of naturally occurring ligands on the weathering rate of stone meal
Group Soil Chemistry and Chemical Soil Quality
Project type thesis
Credits 24-39
Supervisor(s) Walter Schenkeveld, Mathilde Hagens
Examiner(s) Prof.dr R. Comans
Contact info Walter.schenkeveld@wur.nl
Begin date 2021/06/01
End date
Description The application of stone meal (rock dust) in natural and agroecosystems has recently received a lot of attention for its great potential to concurrently improve soil quality and sequester carbon. For instance, it’s currently being tested as a remedy for the deteriorating quality of Dutch forests as a result of excessive nitrogen deposition, which leads to soil acidification.

Finely ground rocks containing primary minerals are distributed over the soil surface, where these minerals are exposed to weathering processes leading to (partial) dissolution. During these dissolution reactions, alkalinity is generated and nutrients like K, P, Ca and Mg are released from the minerals increasing their (potential) bioavailability.

In order to enhance the quality of the soil on meaningful timescales, it’s key that dissolution processes are sufficiently fast, and that the minerals have a suitable elemental composition. Dissolution rates will depend on the size of the stone meal particles, the type of minerals they contain, but also on environmental conditions like pH.

It’s well established that naturally occurring ligands, e.g. in plant and microbial exudates, can enhance mineral weathering rates through ligand-promoted dissolution and by lowering the solution saturation state of minerals. Especially in environments with a high biological activity, like the rhizosphere, ligands may control the overall weathering rate and the rates at which nutrients become available. Still, the effect of plant and microbial ligands on the dissolution rates of minerals in stone meal has hardly been examined yet.

This knowledge gap will be addressed in this MSc thesis project. For a set of minerals commonly found in stone meal, the effect of biogenic ligands (e.g. citrate, oxalate, DFOB) and humic substances on the dissolution rate will be examined at several pH values in the soil pH range (3-9). This will be done in batch dissolution experiments with mineral suspensions to which ligands solutions will be added. The results from this study will improve our understanding of the contribution of natural ligands to the successful application of stone meal.
Used skills Literature review, proposal writing, laboratory work (material characterization, kinetic batch dissolution experiments), data processing, thesis writing
Requirements Some laboratory experience, as well as 12 credits of SOC/SBL-courses in either one of the following combinations:
1) SBL-21806 Soil Quality and SOC-34806 Applications in Soil and Water Chemistry;
2) SOC-21306 Soil Pollution and Soil Protection and SOC-34806 Applications in Soil and Water Chemistry;
3) SBL-35306 The Carbon Dilemma and SOC-34806 Applications in Soil and Water Chemistry;
or 4) SOC-36306 Biogeochemical Cycles and Climate Change Mitigation and SBL-35306 The Carbon Dilemma.