Articles | Volume 4, issue 1
SOIL, 4, 23–35, 2018
SOIL, 4, 23–35, 2018

Original research article 12 Jan 2018

Original research article | 12 Jan 2018

Bone char effects on soil: sequential fractionations and XANES spectroscopy

Mohsen Morshedizad1, Kerstin Panten2, Wantana Klysubun3, and Peter Leinweber1 Mohsen Morshedizad et al.
  • 1Soil Science, Faculty of Agricultural and Environmental Sciences, University of Rostock, Justus-von-Liebig Weg 6, 18051 Rostock, Germany
  • 2Institute for Crop and Soil Science, Julius Kühn Institute, Bundesallee 50, D-38116 Braunschweig, Germany
  • 3Synchrotron Light Research Institute, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand

Abstract. The acceptability of novel bone char fertilizers depends on their P release, but reactions at bone char surfaces and impacts on soil P speciation are insufficiently known. By using sequential fractionation and synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy we investigated whether and how the chemical composition of bone char particles has been altered in soil and has consequently affected the P speciation of amended soils. Therefore, two different kinds of bone char particles (BC produced by the pyrolysis of degreased animal bone chips at 800 °C and BCplus, a BC enriched with reduced sulfur compounds) were manually separated from the soil at the end of two different experiments: incubation leaching and ryegrass cultivation. Sequential P fractionation of amended soils showed P enrichment in all fractions compared to the control. The most P increase between all treatments significantly occurred in the NaOH–P and resin-P fractions in response to BCplus application in both incubation-leaching and ryegrass cultivation experiments. This increase in the readily available P fraction in BCplus-treated soils was confirmed by linear combination fitting (LCF) analysis on P K-edge XANES spectra of BC particles and amended soils. The proportion of Ca hydroxyapatite decreased, whereas the proportion of CaHPO4 increased in BCplus particles after amended soils had been incubated and leached and cropped by ryegrass. Based on P XANES speciation as determined by LCF analysis, the proportion of inorganic Ca(H2PO4)2 increased in amended soils after BCplus application. These results indicate that soil amendment with BCplus particles leads to elevated P concentration and maintains more soluble P species than BC particles even after 230 days of ryegrass cultivation.

Short summary
We investigated how the composition of bone char (BC) particles altered in soil and affected the soil P speciation by fractionation and X-ray absorption near-edge structure spectroscopy. Bone char particles (BC from pyrolysis of bone chips and BCplus, a BC enriched with S compounds) were collected at the end of incubation-leaching and ryegrass cultivation trials. Soil amendment with BCplus led to elevated P concentrations and maintained more soluble P species than BC even after ryegrass growth.