Bone char effects on soil: sequential fractionations and XANES spectroscopy

Mohsen Morshedizad,Kerstin Panten,Wantana Klysubun,Peter Leinweber

doi:10.5194/soil-4-23-2018

Abstract

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.

Highlights

On the global scale, readily available sources of phosphorus (P), a crucial macronutrient element for agricultural production, are being faced with scarcity and overpricing (Scholz et al, 2013; Van Vuuren et al, 2010)
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 affected the P speciation of amended soils
Two particle size fractions (1–2 and 2–4 mm) of bone chars were incubated with a silt loam soil (BC produced by the pyrolysis of degreased animal bone chips at 800 ◦C and BCplus as a surface-modified bone char” (BC) obtained by blending with reduced S-containing compounds composed of 60 % elemental S, 30 % calcium sulfate dehydrate and 10 % methanesulfonate (Zimmer et al, unpublished results of S X-ray absorption near-edge fine structure spectroscopy) in a commercial biogas desulfurization process; patent application DE 212012000046U1; http:www.google.com/patents/ DE212012000046U1?cl=en&hl=de)

Summary

Introduction

Readily available sources of phosphorus (P), a crucial macronutrient element for agricultural production, are being faced with scarcity and overpricing (Scholz et al, 2013; Van Vuuren et al, 2010). Many recent studies have targeted sustainable agriculture through improving P availability from applied fertilizers (Delgado et al, 2002; Schröder et al, 2011), increasing P-uptake efficiency from organic and inorganic P pools in the soil (Kaur and Reddy, 2014) and developing new technologies for P recycling from human and animal waste (Siebers and Leinweber, 2013; Herzel et al, 2016). Morshedizad et al.: Bone char effects on soil: sequential fractionations and XANES spectroscopy rock phosphates (Powers, 1923; Lee et al, 1987; Fan et al, 2002) or meat and bone ashes (Schnug et al, 2003)

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