Effect of biochar application at a trace-elements polluted area on soil carbon stability
Authors: Campos Díaz de Mayorga Paloma , Miller Ana Z. , Knicker Heike , Sánchez-Martín Águeda , Fernández-Boy Elena , De la Rosa José María 
Published: March 2020

&lt;p&gt;Biochar, the solid carbonaceous material produced by pyrolysis of biomass, is a promising alternative for restoring degraded soils [1]. Specifically, biochar has been reported to increase agronomic productivity of acidic soils. Nevertheless, the theoretical high stability and recalcitrance of biochar is being questioned by recent studies [2]. In addition, the alterations on biochar C after its application into low C soil is still under debate. Thus, this study intends to evaluate the changes in carbon stability when biochars from different feedstock are applied into trace element polluted soils.&lt;/p&gt;&lt;p&gt;For this purpose, biochars were produced from rice husk-RHB, olive pit-OPB and almond shell-ASB using a steel batch reactor (temperature of 500 &amp;#186;C; reaction time of 2 h under N&lt;sub&gt;2&lt;/sub&gt; atmosphere with a heating rate of 20 &amp;#186;C min&lt;sup&gt;-&lt;/sup&gt;&lt;sup&gt;1&lt;/sup&gt;). A certified wood biochar (CWB) was also studied for comparative purposes. Two soils with a moderate and a high concentration of trace elements (called MPS and HPS respectively) were sampled for this study. Mixtures of each soil and 10 % (w/w) of the biochars were prepared in triplicates. Each pot was inoculated with 1 ml of a standard microbial suspension, the moisture was adjusted to 50 % of the water holding capacity and incubated in the automatic respirometer Respicond (Nordgren Innovations, Sweden) at 25 &amp;#186;C for 60 days similarly to the procedure described by De la Rosa et al (2018) [2]. The CO&lt;sub&gt;2&lt;/sub&gt; released was measured automatically every 6 h and the kinetics of the biological decomposition of the materials were fitted by a double exponential model. Results showed that the feedstock nature influenced the decomposition rates. Thus, the biochar stability of the tested materials followed the order ASB&gt;RHB&gt;OPB according to MTR&lt;sub&gt;2&lt;/sub&gt;.&lt;/p&gt;&lt;p&gt;Soil respiration showed a different C decomposition rate in both soils, having greater mean residence time in HPS (MTR&lt;sub&gt;2&lt;/sub&gt;=14.9 years) than in MPS (MTR&lt;sub&gt;2&lt;/sub&gt;=5.7 years). Our findings suggest that biochar addition increased the MTR&lt;sub&gt;2&lt;/sub&gt; of the slow C pool in both soils.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;[1] Lehmann, J., Joseph, S., 2015. Biochar for environmental management: science and technology. 2nd ed. London &amp; New York: Earthscan from Routledge.&lt;/p&gt;&lt;p&gt;[2] De la Rosa, J.M., Rosado, M., Paneque, M., Miller, A.Z., Knicker, H., 2018. Effects of aging under field conditions on biochar structure and composition: Implications for biochar stability in soils. Science of the Total Environment 613-614, 969-976.&lt;/p&gt;&lt;p&gt;Acknowledgements:&lt;/p&gt;&lt;p&gt;The former Spanish Ministry of Economy, Industry and Competitiveness (MINEICO) and AEI/FEDER are thanked for funding the projects CGL2016-76498-R and GL2015-64811-P. P. Campos thanks the &amp;#8220;Fundaci&amp;#243;n Tatiana P&amp;#233;rez de Guzm&amp;#225;n el Bueno&amp;#8221; for funding her PhD.&lt;/p&gt;