Epsilon Archive for Student Projects

Abstract

Phosphorus (P) is an essential macronutrient for plant growth, yet its availability in forest soils can be limited by the strong adsorption onto mineral surfaces. This thesis studied the sorption behaviour of P to synthetic ferrihydrite (Fh) and proto-imogolite (PIM), two abundant secondary minerals in the B horizons of Swedish Podzols, as a function of pH. P sorption decreased with increasing pH for both Fh and PIM, due to a less positively charged surface. P sorbed more strongly to PIM at pH >5.5 than to Fh, but less below pH 4.9, due to dissolution of PIM. Furthermore, the influence of two organic acid anions, D-gluconate (GL) and oxalate (Ox) was tested. Both acid anions were found to be able to mobilise P from Fh and PIM and thus make it more bioavailable to plants. Ox was more efficient at mobilising P than GL, especially from PIM. Its main mechanism was through the dissolution of the mineral, with a higher ability to dissolve PIM than Fh, thus releasing more P. GL could not dissolve the minerals when P was present. It hindered P sorption through competition for the same binding sites. Experimental data from single sorbent system were used to optimise complexation constants for the Fh CD-MUSIC Model (Gustafsson and Antelo 2022) and the PIM Basic Stern Model (Flor´en et al. in preparation). While modelled sorption behaviour to Fh was tolerable, sorption to PIM could not be accurately portrayed due to experimental errors as well as potentially inaccurate fundamental properties used as input. Only the P sorption to PIM in the single sorbent system could be successfully represented.