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Doctoral thesis, 2011

Sulfur cycling in Swedish arable soils

Boye, Kristin;

Abstract

Sulfur (S) is an essential plant nutrient. Decreased S deposition in combination with a switch to high-analysis N/P-fertilizers has increased the need for S fertilization. Thus, soil research directed at understanding soil sulfur properties and processes has intensified. However, the methodology at hand has been insufficient for determining relationships between soil properties, S cycling and S availability to crops. In this thesis, recently developed methods were used to study the effect on soil S by two management systems, livestock production and arable crop production, at five different locations within a Swedish long-term fertility field experimental series. In an open incubation study, and a pot trial, where isotopic labeling (35S) was used to trace S transformations, S cycling rates were higher in the livestock system, especially in one soil (Orup). The S delivering capacity of all soils was too low to avoid S deficiency in ryegrass without mineral S application. Observed differences in S cycling patterns could not be satisfactorily explained by soil properties; however, multivariate analyses indicated net S mineralization was negatively related to C/N-ratios and SO42- content. The extent of organic S stabilization through organomineral association and physical protection within microaggregates was investigated by an extraction/dispersion method. The relative distribution between the pools varied between soils, with the residual (non-extractable) pool always being largest; however, only the physically protected fraction was negatively related to plant S uptake. All soil organic S pools were involved in S transformations, although the residual pool was less active than the other pools. Chemical speciation of S in soils and soil fractions was determined by S K-edge X-Ray Absorption Near-Edge Structure (XANES) spectroscopy. A new method for fitting spectra provided reliable quantification of S species by using internally calibrated spectra of dilute (30mM) model compounds. The response of S speciation to management system differed between soils, but highly oxidized S dominated in the organomineral fractions, and intermediate forms of oxidized S in the residual fraction. In conclusion, soil organic S speciation can be accurately quantified by S K-edge XANES spectroscopy. The speciation differs between organomineral associated S and residual S. Treatment effects are dependent on soil type, but S cycling is stimulated by long-term farmyard manure application, as seen in the livestock system.

Keywords

sulphur; soil fertility; plant soil relations; nutrient availability; sulphur fertilizers; farmyard manure; organic matter; x ray spectroscopy; alternative agriculture; conventional farming; field experimentation; sweden

Published in

Acta Universitatis Agriculturae Sueciae

2011, number: 2011:74
ISBN: 978-91-576-7618-4
Publisher: Department of Soil and Environment, Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Soil and Environment

UKÄ Subject classification

Soil Science
Agricultural Science

URI (permanent link to this page)

https://res.slu.se/id/publ/35124