Stability Of Rice Straw-derived Biochar In Paddy Soil

Biomass derived carbon (biochar), which is stable both chemically and biologically, could remain in the environment for hundreds or even thousands of years. In addition, biochar has the potential to improve soil quality. Therefore, applicating biomass to the soil in the form of biochar is thought to be a promising technology to reduce greenhouse gas emissions. This research intended to study the mineralization characteristics and stability of rice straw-derived biochar (RSC) in the flooded paddy soil using the technology of stable carbon isotope labeling and analysis in the laboratory. Furthermore, through the techniques of elemental analysis, Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectrometer (FTIR) and so on, this paper studied the stability mechanisms of RSC in the flooded paddy soil. These results provided important theoretical basis for the technology of applicating biochar to soil to realize carbon sequestration in the agricultural ecosystem in China. The main results of this study are as follows:1. The greenhouse experiment was carried out to investigate the mineralization characteristics of13C-labelled RSC and the effects of rice on its degradation in paddy soil. The results showed that biochar mineralized quite slowly in paddy soil with a mineralization rate of5.9×10-5%d-1at the12th day of preincubation time. Furthermore, under the rice-planting condition, rice and microorganism were able to utilize very little biochar at a rate of0.047%and0.0016%, respectively. It indicated that the RSC was relatively stable in paddy soil with low degradation rates both abiotically and biotically.2. Based on the results of mineralization characteristics, the techniques such as elemental analysis, SEM, FTIR was used to study the stability mechanisms of RSC in the flooded paddy. It was found that RSC was rich in carbon content, which was higher than60%. And RSC was thermally stable within1000℃whose mass loss was less than26%, indicating that carbon of biochar was resistant to thermal degradation. Moreover, carbon structure of biochar was mainly in the functional groups of unsaturated alkyl (C-H in olefin), aliphat (C-O-C) and aromat (C=C, C-H). The oxidation both abiotically and biotically had no significant effects on the functional groups of biochar after209days of incubation, demonstrating the stability of chemical structure of RSC. However, when biochar was exposed in the environment, the oxidation in the surface of biochar was relatively strong. Moreover, rice promoted the oxidation in the surface of biochar. After entering the soil, RSC was likely to interact with soil minerals such as Si, Ca, which would protect biochar from mineralization.