Abstract

Cultivated organic soils make a significant contribution to phosphorus (P) leaching losses from agricultural land, despite occupying a small proportion of cultivated area. However, less is known about P mobilisation processes and the P forms present in peat soils compared with mineral soils. In this study, P forms and their distribution with depth were investigated in two cultivated Histosol profiles, using a combination of wet chemical extraction and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy.Both profiles had elevated P content in the topsoil, amounting to around 40 mmol kg(-1), and P speciation in both profiles was strongly dominated by organic P. Topsoils were particularly rich in organic P (P-org), with relative proportions of up to 80%. Inorganic P in the profiles was almost exclusively adsorbed to surface reactive aluminium (Al) and iron (Fe) minerals. In one of the pro-files, small contributions of Ca-phosphates were detected.A commonly used P saturation index (PSI) based on ammonium-oxalate extraction indicated a low to moderate risk of P leaching from both profiles. However, the capacity of soil Al and Fe to retain P in organic soils could be reduced by high competition from organic compounds for sorption sites. This is not directly accounted for in PSI and similar indices.Accumulation of P-org in the topsoil may be attributable by microbial peat decomposition and transformation of mineral fertiliser P by both microbiota and crops. Moreover, high carbon-phosphorus ratio in the surface peat material in both profiles suggests reduced net mineralisation of P-org in the two soils. However, advancing microbial peat decomposition will eventually lead to complete loss of peat horizons and to mineralisation of P-org. Hence, P-org in both profiles represents a huge potentially mobilised P pool.

Keywords

Histosol; organic phosphorus; phosphorus saturation; soil aluminium; soil iron; X-ray absorption spectroscopy

Published in

Journal of Plant Nutrition and Soil Science
2020, Volume: 183, number: 3, pages: 367-381
Publisher: WILEY-V C H VERLAG GMBH

SLU Authors

• Schmieder, Frank

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Gustafsson, Jon-Petter

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Riddle, Matthew

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Kirchmann, Holger

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Bergström, Lars

  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Soil Science


Publication identifier

DOI: https://doi.org/10.1002/jpln.201900129

Permanent link to this page (URI)

https://res.slu.se/id/publ/105698