The effects of long-term rice straw and biochar return on soil humus composition and structure in paddy soil

Abstract

The aim of this study was to evaluate the effects of continuous application of rice straw and biochar for 10 years on soil humus composition and structure in paddy soil. A 10-year field experiment was conducted in a paddy field and included three treatments: rice straw biochar (SC); rice straw (RS), no biochar or rice straw. The elemental analyser, Fourier transform infrared (FT-IR) spectrum, and three-dimensional excitation-emission matrix (3D EEM) fluorescence spectroscopy with fluorescence regional integration (FRI) analysis were used to study the soil humus composition and structure under different treatments. The results verified that the incorporation of rice straw and biochar significantly improved soil pH values and the soil organic carbon contents compared with the control. Rice straw significantly increased the contents of extractable humus, humic acid (HA) and fulvic acid in soil, while biochar only significantly affected HA and humic degree values. The molecular structure of HA affected by biochar is characterised by high humification and aromaticity, but rice straw increased the aliphaticity of the HA structure, as presented by elemental composition. Moreover, 3D EEM spectroscopy combined with FRI analysis showed that RS treatment formed soil humus had more aliphatic compounds, while SC treatment increased the aromatic components of humus. These results suggest that rice straw promotes the renewal of humus, and biochar enhances the humification degree of humus and the aromaticity of HA.

Keywords

• ecosystem
• ft-ir spectrum
• carbon cycle
• microorganism
• structural properties