Thesis subject

Impacts of heavy metal inputs on the long term immobilization and release in agricultural soils

The Environmental Systems Analysis Group provides the possibility for students to do their thesis in collaboration with our group. This is one of many possible thesis subjects. Please feel free to contact professor De Vries (right) for more information.

Since early 1940, European agriculture has intensified greatly with large inputs of nitrogen (N) and phosphorous (P) by fertilizers and manure. Furthermore, elevated inputs of metals, such as cadmium (Cd), copper (Cu) and zinc (Zn), by fertilizer and manure applications and atmospheric deposition has caused at several places an increase in metal accumulation in soils with related impacts on plant uptake and runoff to surface waters. In this context, it is crucial to make a distinction between Cd, that has only toxic impacts at high concentrations, and Cu and Zn, which are crucial micronutrients in view of plant nutrition and animal health. Zinc deficiency is even a common global phenomenon and it also occurs in Europe, e.g. in light textured, low organic carbon soils with low Zn concentrations or on alkaline soils in which Zn solubility is reduced. The same holds to a lesser extend for Cu. A large part of Znand Cu in soils is (geo)chemically inert (practically defined as difference between the total Zn pool in soil and the pool extractable by dilute (0.43N) nitric acid). Current European mass balance studies show that the reactive Zn pool (i.e. extractable by 0.43 N HNO3) decreases (uptake + leaching > supply) which will lead to Zn deficient soils and Cu pools also decrease in certain parts of Europe. Current dynamic models, however, are not capable to account for changes between the reactive and inert fraction. As of now it is unclear: (i) how much of Zn (and Cu) added to soils remains available in soil and (ii) if there is re-release of inert Zn (and Cu) upon depletion of reactive Zn (and Cu) in soils. This lack of knowledge on how to include immobilization or release of Zn (and Cu) in dynamic metal models, affects the predicted long term changes of Zn (and Cu) in soil and hence the potential shortage in soils in view of crop production and product quality. Questions to be addressed in thesis:

  1. Can we mimic the release or immobilization of Zn (and Cu) in soils of different origin (clay/sand/low pH etc)
  2. Does the form of added Zn (and Cu), specifically fertilizer vs compost vs manure, affect the immobilization?
  3. Is there a release from the inert pool after depletion of the reactive pool?

The ultimate aim is to improve current dynamic metal models, used at Alterra at regional scale, based on the experimental results and simulate long term impacts of different scenarios for characteristic soil vegetation combinations in Europe