Short-term effects of biochar on soil CO2 efflux in boreal Scots pine forests

Xudan Zhu

doi:10.5194/egusphere-egu2020-21914

Abstract

&lt;p&gt;The use of biochar as a soil amendment has been proposed to increase the carbon (C) sequestration in soils. However, a more rapid soil organic matter turnover after biochar application might reduce the effectiveness of biochar applications for C sequestration. Data on the effects of biochar on soil C turnover is particularly important in boreal forests where large quantities of forest harvest residues would be available as feedstock for biochar production. To better understand the effects of biochar on boreal forest soil, we established a split-plot experiment where two spruce biochar produced with different temperatures (500&amp;#176;C and 650&amp;#176;C) were applied at a rate of 1.0 kg m&lt;sup&gt;-2&lt;/sup&gt; and 0.5 kg m&lt;sup&gt;-2&lt;/sup&gt; in a young xeric Scots pine forest in southern Finland. Measurement of soil CO&lt;sub&gt;2&lt;/sub&gt; effluxes and microbial biomass were used to investigate changes in soil C dynamics. Biochar application increased the rate of soil CO&lt;sub&gt;2&lt;/sub&gt; efflux by 10.6% across all biochar treatments and significantly (P&lt;0.05) in 1.0 kg m&lt;sup&gt;-2&lt;/sup&gt; treatments. Soil microbial biomass remained unchanged. Soil temperature was 0.1 to 0.5&amp;#176;C higher in the biochar-amended treatments. Further analysis revealed that when soil CO&lt;sub&gt;2&lt;/sub&gt; efflux was corrected for the changes in soil temperature and soil moisture, there were no significant differences between treatments. We conclude that increase in soil CO&lt;sub&gt;2&lt;/sub&gt; efflux was attributed to warmer soils at the initial stage after biochar application to the soil surface; changes in soil chemical properties did not have any detectable effect on soil respiration.&lt;/p&gt;

Highlights

Biochar is a C-rich material produced by pyrolyzing biomass or other organic materials, such as agricultural crop residues, wood, and green waste in an oxygen-depleted environment (Ahmed and Schoenau 2015)
Palviainen et al (2018) investigated the long-term effect of biochar application on carbon and nitrogen fluxes in the same site and found that soil CO2 effluxes showed no clear response to biochar addition
Our results suggest that changes in the physical environment dominate the response of soil CO2 efflux after biochar application

Summary

Introduction

Biochar is a C-rich material produced by pyrolyzing biomass or other organic materials, such as agricultural crop residues, wood, and green waste in an oxygen-depleted environment (Ahmed and Schoenau 2015). In 2001, the term “biochar” was coined after Glaeser describing “Terra preta” soils (Glaser et al 2001). It is used as a soil amendment to increase productivity, restore soil fertility, sequester C in soil, and reduce atmospheric CO2 concentration (Woolf 2008; Van Zwieten et al 2010; Wang et al 2014). The majority of studies on the effects of biochar application on soils have been on agricultural soils (Prayogo et al 2014; Lu et al 2014; Zhang et al 2017). The effects of newly added biochar on forest ecosystems are still uncertain

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