Effects Of Rice-straw Biochar Application On Ammonia Volatilization From Agricultural Soil In Rice-wheat Rotation

Biochar has widely used in farmland ecosystem to deal with major problems such as resource utilization,soil improvement and environmental pollution.Due to its unique properties,biochar will change the physical and chemical properties of soil and affect the nitrogen cycle.Under the background of reducing fertilizer use while increasing efficiency,it has a great significance to research the effects of biochar on soil nitrogen cycle.NH₃volatilization occupies an important proportion in the soil nitrogen loss,which not only reduces the nitrogen use efficiency,but also accelerates the ecological environment deterioration.In this research,we evaluated the effects of long-term rice-straw biochar amendment on soil NH₃volatilization,the physical and chemical properties of surface water and soil in rice-wheat rotation soil.We also explored the effects of rice-straw biochar application on NH₃emissions and functional microbial diversity to reveal the mechanism of the influences of biochar application on NH₃volatilization in different water contents.The main conclusions are summarized as follows:?1?The effects of rice-straw biochar application on NH₃volatilization from rice-wheat rotation in Taihu lake basin was observed by continuous pumping method.The results showed that the soil NH₃volatilization rate increased rapidly,reached a peak in 2-3 days and then decreased gradually in rice and wheat seasons.Compared with routine fertilization,biochar significantly reduced the soil NH₃emissions with a decrease of 6.11%?28.28%in rice season and 20.41%?49.60%in wheat season.The rice-straw return to the field can decrease the soil NH₃emissions by 50.68%?51.89%.In summary,the medium amount of biochar?11.25 t/hm²?had the best effect on the control of soil NH₃volatilization.?2?The effects of long-term rice-straw biochar on soil and surface water physical and chemical indexes were measured.The results showed that soil p H,NO₃^--N concentration and urease activity increased significantly,but NH₄⁺-N concentration decreased.And soil temperature did not change by biochar application.Correlation analysis showed that the soil NH₃volatilization in rice season after biochar amendment was mainly positively correlated with NH₄⁺-N concentration and temperature in soil and surface water,with R²between 0.470-0.675?p<0.05?.The soil NH₃volatilization in wheat season was significantly correlated with soil p H,temperature and urease activity,with R²between 0.677-0.755?p<0.05?.Therefore,the main factors influenced NH₃volatilization in rice-wheat rotation under biochar intervention are different.Among which the rice season was mainly influenced by surface water NH₄⁺-N concentration,while the wheat season was mainly influenced by soil p H,temperature and soil urease.?3?The effects of biochar on soil NH₃volatilization,ammonia-oxidizing function gene,urease gene and the physicochemical properties of soil and surface water under different water content were investigated by paddy-upland transformation experiments.The results showed that biochar amendent increased the soil NH₃emissions by 30%WHC,60%WHC and 90%WHC?30%,60%and 90%of the maximum soil water capacity in the field?,with an increase rate of 114%?702%.Soil p H and urease activity are positively related to soil ammonia volatilization with0.748-0.931?p<0.01?.The reason may be that biochar has a high alkalinity,which will increase soil p H to interfere with the alkalinity balance of NH₄⁺conversion to NH₃in the soil liquid phase,thus promoting soil NH₃emissions.However,the biochar reduced the NH₃loss of flooded soil?water:soil 2:1?by 29.31%?39.69%,significantly.Correlation analysis showed that surface water NH₄⁺-N concentration and copies of AOA and AOB genes were significantly correlated to NH₃volatilization with 0.658,0.657 and 0.722?p<0.05?,accordingly.The reason may be that biochar significantly increases the abundance of AOA and AOB genes,which promotes ammonia oxidation to decrease the soil NH₄⁺-N concentration and thus reducing NH₃emissions.