Charcoal Fine Residues Effects on Soil Organic Matter Humic Substances, Composition, and Biodegradability

Otávio Dos Anjos Leal,José A González-Pérez,José María De La Rosa,Daniela Piaz Barbosa Leal,Deborah Pinheiro Dick,Heike Knicker,Gabriel Soares Campos

doi:10.3390/agronomy9070384

Abstract

Biochar has been shown as a potential mean to enhance carbon sequestration in the soil. In Brazil, approximately 15% of the produced charcoal is discarded as charcoal fines, which are chemically similar to biochar. Therefore, we aimed to test charcoal fines as a strategy to increase soil carbon sequestration. Charcoal fines of hardwood Mimosa scabrella were incorporated into a Cambisol down to 10 cm (T1 = 0 and T4 = 40 Mg ha−1) in Southern Brazil. Soil samples were collected (0–30 cm) 20 months after charcoal amendment. Soil organic matter (SOM) acid extract, humic acid, fulvic acid, and humin fractions were separated. Solid-state 13C nuclear magnetic resonance (NMR) spectra from charcoal and SOM in T1 and T4 were obtained before and after 165 days of incubation under controlled conditions. Charcoal increased soil carbon as fulvic (10–20 cm) and humic acids (10–30 cm) and, especially, as humin (0–5 cm), which probably occurred due to the hydrophobic character of the charcoal. The 13C NMR spectra and mean residence times (MRT) measured from incubation essays indicated that the charred material decomposed relatively fast and MRT of T1 and T4 samples were similar. It follows that the charcoal fines underwent similar decomposition as SOM, despite the high charcoal dose applied to the soil and the high aryl C contribution (78%) to the total 13C intensity of the charcoal NMR spectra.

Highlights

In recent years, the literature has reported the potential of biochar as a strategy to mitigate global warming
Found in T4 could be attributed to the considerable amount of charcoal particles remaining near the soil surface, as evidenced, in a previous study, by scanning electron microscopy (SEM) and by the higher C content in the particulate Soil organic matter (SOM) fraction [27]
The CHCl fraction is mainly composed of organic compounds that are originated from the microbial activity and from root exudations

Summary

Introduction

The literature has reported the potential of biochar as a strategy to mitigate global warming. Biochar can enhance carbon (C) sequestration directly when buried into the soil or indirectly by improving soil quality and crop production, enhancing CO2 capture from the atmosphere [1,2]. Biochar is a C-enriched material intentionally produced via pyrolysis of biomass to be applied to the soil as a means to improve C sequestration, soil quality, and crop yield [1,3]. Biochar is distinguished from charcoal since energy generation, industrial use, and domestic cooking are the main purposes of charcoal production. The thermochemical conversion of biomass in pyrogenic C (PyC) is a common process for both biochar and charcoal production [3].

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