Pyrogenic Carbon Lacks Long-Term Persistence in Temperate Arable Soils

Suzanne Lutfalla,Folkert Van Oort,Samuel Abiven,Sabine Houot,Thomas Kätterer,Bent T Christensen,Andy J Macdonald,Daniel B Wiedemeier,Claire Chenu,Pierre Barré

doi:10.3389/feart.2017.00096

Abstract

Pyrogenic organic carbon (PyOC) derived from incomplete burning of biomass is considered the most persistent fraction of soil organic carbon (SOC), being expected to remain in soil for centuries. However, PyOC persistence has seldom been evaluated under field conditions. Based on a unique set of soils from five European long-term bare fallows (LTBF), i.e., vegetation-free field experiments, we provide the first direct comparison between PyOC and SOC persistence in temperate arable soils. We found that soil PyOC contents decreased more rapidly than expected from current concepts, the mean residence time (MRT) of native PyOC being just 1.6 times longer than that of SOC. At the oldest experimental site, 55% of the initial PyOC remained after 80 years of bare fallow. Our results suggest that while the potential for long-term C storage exists, the persistence of PyOC in soil may currently be overestimated.

Highlights

Pyrogenic Organic Carbon (PyOC) is a charred residue derived from the incomplete burning of biomass and is a native component of most soils
We found contents of soil PyOC detected by the Benzene Polycarboxylic Acid (BPCA) method to decrease surprisingly fast at all long-term bare fallows (LTBF) sites (Figure 1 and Table 2)
Initial concentrations varied between 0.38 mg PyOCC g−1 soil and 0.75 mg PyOCC g−1 soil (Rothamsted1 and 2) corresponding to 2 and 4% of the total organic carbon (TOC) contents (TOC = PyOC + soil organic carbon (SOC))

Summary

Introduction

Pyrogenic Organic Carbon (PyOC) is a charred residue derived from the incomplete burning of biomass and is a native component of most soils. PyOC represents on average about 14% of the soil organic carbon (SOC) and ranges between 0 and 60% depending on the conditions of fire, soils and climate (Reisser et al, 2016). Recent reviews suggest that the persistence of PyOC in soil may range from a few years to millennia (Singh et al, 2012a; Lehmann et al, 2015). These differences can be explained by the heterogeneity of PyOC material, and by the different methods used to assess its presence in soils. Assessing the MRT of PyOC is complex, because of the large time span that should be considered. Lehmann et al (2015) described the existing approaches and their current limitations, among which: laboratory soil incubations, field setups, and space for time approaches

Methods

Results

Conclusion