Effects Of Biochar On Soil Respiration And NEE In AWD Paddy Fields

To achieve carbon peak by 2030 and carbon neutral by 2060 is a major strategic decision announced by China to the world.As a major source of greenhouse gases,rice fields play a crucial role in the global carbon cycle.As a big rice-farming country,carbon sequestration and emission reduction in rice field is urgent.Biochar has become a research hotspot in the field of agriculture because of its great potential in carbon sequestration and emission reduction,soil water and fertilizer conservation capacity and ecological environment improvement,as well as its wide material sources and broad prospects for industrial development.However,different material types lead to significant differences in the characteristics of biochar,and its carbon sequestration potential is very different.Especially under alternate wetting and drying irrigation,the rice field was always in the environment of soil water saturation and unsaturated,and soil oxidation and reduction changed rapidly,and the carbon cycle of rice field carbon accumulation and net ecosystem carbon exchange changed significantly.In this study,straw,shell and sawdust biochar were applied to dry and wet alternate paddy fields,and the effects of different biochar materials on soil organic carbon,DOC/TOC,plant carbon accumulation and net ecosystem carbon exchange were investigated through a two-year in-situ field experiment.This experiment comprehensively revealed the generation mechanism and emission law of greenhouse gas CO₂in rice field by combining theoretical analysis and experiment,aiming to enrich the theory of rice water-saving irrigation,so as to enhance the carbon sequestration ability of paddy soil at the same time.It provides theoretical and practical basis for reducing agricultural greenhouse gas emissions to alleviate global climate change and improve green and sustainable development of rice paddy ecosystem in China.（1）AWD and biochar treatments both increased the amount of NEE carbon sequestration.Compared with CF,AWD treatment promoted NEE carbon sequestration by significantly increasing the amount of NEE carbon sequestration at the second topdressing stage,and NEE carbon sequestration reached a significant level at the end of full growth in2021.Compared with no application of biochar,except for MS treatment in 2020,the application of biochar with different materials promoted the carbon sequestration of NEE by affecting the carbon sequestration of plants.In addition,the fixed amount of NEE increased significantly with fertilizer application in the short term.（2）AWD and biochar treatments increased soil respiration rate.Compared with CF,AWD treatment increased soil oxygen flux and significantly increased soil respiration rate during the whole growth period.The application of biochar increased soil porosity and promoted soil respiration in paddy fields,which showed a significant effect in 2020.Different biochar materials had different effects on soil respiration rate,and the enhanced effects were RH（19.5%）>SD（15.3%）>MS（10.8%）in 2021.Interaction between AWD and biochar Soil respiration increased by 57.0%in I_AWDB₀treatment in 2021 compared with I_CFB₀.In addition,soil respiration was mainly affected by fertilization,soil moisture content and soil temperature at 5 cm.（3）AWD and biochar treatment had positive effect on carbon accumulation in plants.Compared with CF,AWD treatment increased carbon accumulation in stem and leaf,reduced carbon transfer to panicle,and decreased plant carbon accumulation.The application of biochar effectively improved the negative effect of AWD.The effects of biochar on carbon sequestration were RH（8.6%-747.62 g/m²）>SD（5.9%-738.83 g/m²）>MS（3.7%-725.72g/m²）.（4）Compared with CF,AWD significantly increased soil surface organic carbon and DOC contents by reducing runoff.The addition of biochar from the external carbon pool increased the contents of surface organic carbon and DOC in the whole rice growing season,and the effective rate of DOC/TOC was RH>SD>MS.Higher surface soil efficiency was beneficial to promote root development and plant growth and development,which stimulated the rice paddy ecosystem to increase yield.（5）The combination of AWD and biochar can significantly improve rice yield.Two years experiment showed that compared with no biochar treatment,the improvement effect of20 t/ha biochar treatment on yield was RH（13.1%）>SD（7.6%）>MS（3.4%）.In the absence of biochar,AWD irrigation yield was smaller than CF in both years,and reached a significant level in 2021.The application of biochar effectively alleviates this problem,so as to achieve the purpose of water-saving and increasing production.Biochar of different materials has different improvement effects,among which I_AWDB_RHhas the best effect for two years,and the average yield increase is 7.5%compared with I_AWDB₀in two years.In conclusion,compared with traditional paddy field management mode(I_CFB₀),AWD combined with rice husk biochar（RH）had the best promoting effect on net CO₂fixation in paddy field ecosystem,and increased plant carbon accumulation,thereby increasing rice yield and reducing rice production resources and environmental costs.The results of this experiment provided a factual basis for reducing the consumption of water and carbon resources for rice growth under the premise of achieving high/stable rice yield.