Converting leguminous green manure into biochar: Changes in chemical composition and C and N mineralization
Journal
Geoderma
Journal Volume
232-234
Pages
581-588
Date Issued
2014
Author(s)
Abstract
Leguminous green manure is an important source of nitrogen (N) and carbon (C) in cropping systems. The fast turnover of leguminous green manure enables it to release N quickly, but limits its effectiveness in maintaining soil organic C content. Converting leguminous green manure into biochar facilitates its use as a soil amendment. In this study, we assessed how the conversion of leguminous green manure (Sesbania roxburghii) into biochar altered its chemical composition and subsequent C and N mineralization. Biomass was charred along a temperature gradient from 200 to 500. °C. Using nuclear magnetic resonance and near-edge X-ray adsorption fine structure spectroscopy, we found that both C and N became enriched in aromatic and heterocyclic aromatic structures in biochar, and this structural change led to a reduction in C and N mineralization rates. The mineralized C decreased from 32.7% of the added C of raw biomass to <. 0.5% of that of biochar at charring temperatures above 400. °C. N release shifted from N mineralization in raw biomass to N immobilization at charring temperatures at 500. °C. As such, soil amended with biochar produced at charring temperatures exceeding 400. °C demonstrated a 25% decrease in dry shoot biomass compared with unamended soil. The results indicated that the C stability of leguminous green manure can be achieved by converting raw material into biochar, but that the charring process may limit it to providing N. © 2014 Elsevier B.V.
SDGs
Type
journal article