Iron speciation in organic matter fractions isolated from soils amended with biochar and organic fertilizers

Beatrice Giannetta, César Plaza, Matthew G. Siebecker, Giuliana Aquilanti, Costantino Vischetti, Jasper R. Plaisier, Miguel Juanco, Donald L. Sparks, Claudio Zaccone

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


The role and distribution of iron (Fe) species in physical soil fractions have received remarkably little attention in field-scale systems. Here, we identify and quantify the Fe phases into two fractions (fine sand, FSa, and fine silt and clay, FSi + Cl), isolated from an agricultural soil unamended and amended with different organic materials, by Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The linear combination fitting and wavelet transform of EXAFS data revealed noticeable differences between unamended FSa and FSi + Cl fractions. Specifically, the FSi + Cl fraction was mainly characterized by ferrihydrite (48%) and Fe(III)-soil organic matter (SOM) complexes (37%), whereas in the FSa fraction, ferrihydrite still represented a major phase (44%), with a lower contribution from Fe(III)-SOM (18%). In the FSa fraction, the addition of the organic amendments resulted in an increase of Fe-SOM complexes (31-35%) and a decrease of ferrihydrite (28-29%). By contrast, in the amended FSi + Cl fractions, the added organic matter led to negligible changes in percent ferrihydrite. Therefore, regardless of the amendment type, the addition of organic matter to soil increased the capability of the coarse fraction (FSa) to stabilize organic carbon, thus pointing out that the role of FSa in carbon sequestration in agricultural soils at a global scale may be overlooked.

Original languageEnglish
Pages (from-to)5093-5101
Number of pages9
JournalEnvironmental Science and Technology
Issue number8
StatePublished - Apr 21 2020


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