Sammanfattning av doktoranduppgiften
Turnover of P in Soils Rich in Organic Matter
Organic soils or histosols are soils that are built up of incompletely decomposed plant material. Their genesis is often related to terrestrialization of shallow surface water bodies. Cultivation of some of these soils can result in high yields. However, previous studies have shown that crop production on organic soils comes with the risk of high nitrogen and phosphorus (P) losses that contribute to the eutrophication of surface waters. The chemical and microbial processes that govern turnover and leaching of P in histosols are still not very well understood. Knowledge about these processes would however be beneficial in regard of developing suitable mitigation strategies to reduce P losses from organic soils.
The overall aim of this project is to close some of these knowledge gaps. A detailed characterization of chemical and physical properties will be carried out on selected Swedish cultivated histosols. This includes the identification and quantification of P forms present in these soils. For this purpose we will rely on advanced spectroscopic techniques such as P31-Nuclear Magnetic Resonance (NMR) and X-ray Absorption Near Edge Structure (XANES) Spectroscopy.
Furthermore we want to identify and study the major processes involved in P mobilization in organic soils. This includes microbial mineralization of organic P forms, which are known to have a high portion on soil P in histosols, as well as the influence of reducing conditions caused by temporary water saturation on reducible mineral P forms. According experiments will be carried out in the lab. It is among others planned to utilize a 33PO4 isotopic dilution technique to quantify organic P mineralization.
We will additionally be able to relate our results to another PhD project in which leaching of P and possible mitigation measures are studied in lysimeter experiments using the same soils as in our project (see Matthew Riddle).