| Biomass-derived charcoal, also named biochar, refers to the highly aromatic substance remaining after pyrolysis of biomass under complete or partial exclusion of oxygen. It can influence the environment through interactions with climate and geology. Due to its characteristics of high stability against decay and high capability of adsorption, biochar plays a significant role in global climate change, carbon cycle in biogeochemical process and environmental system. Serious nutrient loss from soil and large amount of greenhouse gas emissions from paddy field were two substantial issues which prevent the healthy and sustainable development of agriculture in China. In this thesis, lab and field experiments were carried out to study physi-chemical properties, of biochars. and the effects of different biochars on soil nitrogen loss, methane (CH4) and carbon dioxide (CO2) emissions from paddy soil and rice growth. Furthermore, the mechanisms of effects of biochar on CH4 and CO2 emissions were discussed. In addition, some future research directions about biochar in soil ecosystem were put forward. Results of the study would provide a new approach to the reclamation of biomass residues from agriculture and forestry and a new thought for reducing greenhouse gas emissions from rice paddies. The main results of this thesis are as following:(1) Elemental composition, morphological characteristics, surface functional groups and adsorption proporties of bamboo charcoal (BC) and rice straw charcoal (SC) pyrolyzied at 600℃were investigated in this study. Both BC and SC had high porosity. However, there were main differences in their aromatic structure and oxygen-containing functional groups. Specific surface area and total pore volume of BC were higher than those of SC. While the value of pH, electrical conductivity, cation exchange capacity and the numbers of surface acid and basic groups of SC were much higher. Furthermore, SC also had stronger adsorption capacity to ammonium.(2) Influence of BC on nitrogen retention and leaching characteristic at different soil profile depths were investigated using multi-layer soil columns in laboratory. Results showed that ammonium nitrogen (NH4+-N) concentrations in the leachate of the soil columns under the addition of NH4Cl were significantly different at 0-20 cm layer between the treatments with and without BC amendment. Addition of BC to the surface layer soil can retard the vertical transport of NH4+-N to deeper soil within 70 days, indicated by the observation during the first 7 days at 10 cm and the later experimental period at 20 cm. Application of BC could reduce cumulative losses of NH4+-N via leaching at 20 cm by 15.2% at the end of experiment. Electrical conductivity was significantly reduced in the leachate at 10 cm and 20 cm depth of the soil columns with BC addition. Results indicated that BC amendment could significantly reduce nitrogen losses through leaching and increase the utilization efficiency of nitrogen fertilizer in soil.(3) Effect of biochar on CH4 and CO2 emissions from waterlogged paddy soil with and without rice straw added as an additional carbon source were investigated under laboratory condition. Results indicated that adding rice straw significantly increased CH4 and CO2 emissions from the paddy soil. However, CH4 and CO2 emissions could be significantly reduced with the amendment of biochar. CH4 emissions from the paddy soil amended with BC and SC at high level were reduced by 51.1% and 91.2%, respectively, compared with those from the unamended soil. CO2 emission from the waterlogged paddy soil was also reduced with the addition of biochar over a 49 d incubation. SC was more effective than BC in reducing CH4 and CO2 emissions from paddy soils whether with additional carbon source or not. Methanogenic activity in the paddy soil decreased with increasing rates of biochar added; while, the methanogenic archaeal communities in the paddy soil amended with biochar remained unchanged at the final stage of the experiment.(4) The effects of biochar input on nitrogen loss from paddy soil and rice yield were studied under field condition. Initial results suggested that nitrogen losses through effluent and lateral seepage were not significantly influenced by the amendment of biochar when no fertilizer was added. However, the concentrations of NH4+-N, NO3--N and TN of surfacewater and lateral seepage water in the rice paddy showed reducing potential with 1% (w/w) biochar amendment when urea was applied, although there were no remarkable differences. On the other hand, however, SC was much effective in improving rice growth than BC. Rice yield was increased by 19.9% with 1% (w/w) SC amendment compared to that without biochar under no fertilizer condition. While that was 11.2% under urea-added condition. Whereas the boosting effect of BC on rice yield showed less.substantial as compared with SC.
|
PDF Full Text Request