Carbon Sequestration and Fertility after Centennial Time Scale Incorporation of Charcoal into Soil

Irene Criscuoli,Costanza Calzolari,Franco Miglietta,Emanuela Pusceddu,Giorgio Alberti,Roberto Viola,Filippo Favilli,Cristina Martinez,Silvia Baronti,Cornelia Rumpel

doi:10.1371/journal.pone.0091114

Abstract

The addition of pyrogenic carbon (C) in the soil is considered a potential strategy to achieve direct C sequestration and potential reduction of non-CO2 greenhouse gas emissions. In this paper, we investigated the long term effects of charcoal addition on C sequestration and soil physico-chemical properties by studying a series of abandoned charcoal hearths in the Eastern Alps of Italy established in the XIX century. This natural setting can be seen as an analogue of a deliberate experiment with replications. Carbon sequestration was assessed indirectly by comparing the amount of pyrogenic C present in the hearths (23.3±4.7 kg C m−2) with the estimated amount of charcoal that was left on the soil after the carbonization (29.3±5.1 kg C m−2). After taking into account uncertainty associated with parameters’ estimation, we were able to conclude that 80±21% of the C originally added to the soil via charcoal can still be found there and that charcoal has an overall Mean Residence Time of 650±139 years, thus supporting the view that charcoal incorporation is an effective way to sequester atmospheric CO2. We also observed an overall change in the physical properties (hydrophobicity and bulk density) of charcoal hearth soils and an accumulation of nutrients compared to the adjacent soil without charcoal. We caution, however, that our site-specific results should not be generalized without further study.

Highlights

IntroductionThermo-chemical conversion of organic material under limited oxygen supply, within a certain range of temperatures (200– 1200uC), transforms biomass into bio-oil and syngas, which may be used as an energy source, and produces a carbonaceous coproduct (i.e. biomass-derived Pyrogenic-C or charcoal or biochar [1]) which has been proposed as a tool to mitigate climate change and improve soil fertility [2]
Thermo-chemical conversion of organic material under limited oxygen supply, within a certain range of temperatures (200– 1200uC), transforms biomass into bio-oil and syngas, which may be used as an energy source, and produces a carbonaceous coproduct which has been proposed as a tool to mitigate climate change and improve soil fertility [2]
This estimate corresponds to 12% of current global anthropogenic C emissions and includes: a) direct C sequestration, associated with the burial of recalcitrant organic C forms [4]; (b) potential reduction of N2O and CH4 emissions from soils associated with biochar application [5]; and (c) CO2 emissions avoided due to fossil fuel substitution by the energy released by biomass during pyrolysis and gasification

Summary

Introduction

Thermo-chemical conversion of organic material under limited oxygen supply, within a certain range of temperatures (200– 1200uC), transforms biomass into bio-oil and syngas, which may be used as an energy source, and produces a carbonaceous coproduct (i.e. biomass-derived Pyrogenic-C or charcoal or biochar [1]) which has been proposed as a tool to mitigate climate change and improve soil fertility [2]. Several studies have shown that the addition of biochar to both poor and fertile agricultural soils may have beneficial effects on plant yields, amplifying its environmental benefit. These effects are associated with improvements in soil physical [6] and chemical properties [7], microbiological activity [8], temperature increase due to changes in surface albedo [9], hormesis (i.e. favorable biological responses to low exposures; [10]), as well as combinations of several of these different drivers [8]. We were able to assess the effect on physio-chemical soil properties after char addition to soil

Materials and Methods

Results and Discussion

Conclusions