Effects of tobacco stem biochar based fertilizer on nitrogen composition and microbial community structure of tobacco planting soil

【Objective】In order to provide scientific basis for the application of tobacco stem biochar based fertilizer in agricultural production and nitrogen retention in tobacco planting soil，the effects of different amounts of tobacco stem biochar based fertilizer on nitrogen composition and microbial community structure were studied.【Method】Through the field experiment，five treatments were set up：control（CK，no fertilization），tobacco special fertilizer（F，750 kg/ha）， low amount of tobacco stem biochar based fertilizer（LBF，525 kg/ha），medium amount of tobacco stem biochar based fertilizer（MBF，1050 kg/ha）and high amount of tobacco stem biochar based fertilizer（HBF，1575 kg/ha）. The contents of nitrogen（N），phosphorus（P）and potassium（K）treated by MBF and F were the same. Soil nitrogen content，enzyme activity and microbial related indexes were determined from surface soil samples at the mature stage of tobacco leaves. The effects of different amounts of tobacco stem biochar based fertilizer treatment on soil organic nitrogen and inorganic nitrogen content，soil nitrogen cycling enzyme activity and microbial community structure were analyzed.【Result】Compared with CK，the contents of total nitrogen，soluble organic nitrogen，particulate organic nitrogen and ammonium nitrogen in soil were significantly increased（P<0.05，the same below），and each index increased with the increase of the amount of biochar based fertilizer. Under the same fertility，total nitrogen content increased by 5.41% and 7.43%， soluble organic nitrogen content increased by 35.65% and 62.45%，particulate organic nitrogen content increased by 26.83% and 37.71%，ammonium nitrogen content increased by 109.59% and 200.65% respectively in MBF and HBF treatments compared with F treatment. Compared with CK，catalase activity of LBF，MBF and HBF treatment was significantly increased by 22.13%，35.66% and 48.43%，and urease activity was significantly increased by 37.72%，45.50% and 62.08%，respectively. Compared with F treatment，the catalase activity of MBF and HBF treatments was significantly increased by 21.29% and 32.70%，and urease activity was significantly increased by 5.33% and 17.33%，respectively. After the application of fertilizers，the soil microbial biomass nitrogen content significantly increased. The order of each treatment was HBF>MBF>LBF>F>CK. The microbial biomass nitrogen content of LBF，MBF，and HBF treatments increased by 31.83%，44.32%，and 59.84% compared to F treatment，respectively. The application of tobacco stem biochar based fertilizer increased the richness and diversity of soil bacterial communities，which was related to the application amount. Among them，the Chao1 index and Shannon index of HBF treatment were the highest，significantly increased by 4.38% and 5.92% compared to CK，and significantly increased by 2.68% and 3.46% compared to F treatment，respectively. The application of tobacco stem biochar based fertilizer also affected the composition of bacterial communities. Compared with CK，LBF，MBF，and HBF treatments reduced the relative abundance of Proteobacteria by 11.14%- 15.16%，increased the relative abundance of Actinobacteria by 6.50%-10.89%，and increased the relative abundance of Rhizomicrobium by 177.00%-203.00%. The redundancy analysis results indicated that the soil total nitrogen，soluble organic nitrogen，ammonium nitrogen，particulate organic nitrogen contents，urease and catalase activities were positively correlated with Actinobacteria，Saccharibacteria and Firmicutes，but negatively correlated with Proteobacteria，Chloroflexi and Nitrospirae.【Conclusion】Applying tobacco stem biochar based fertilizer can increase soil nitrogen component， regulate bacterial community structure，and the treatment effect of medium and high amounts of tobacco stem biochar based fertilizer is better. Under the same fertility，the effect of applying tobacco stem biochar based fertilizer is better than that of tobacco specific fertilizer. In actual production，considering production costs and application effects，it is more suitable to use a medium amount of tobacco stem biochar based fertilizer treatment（1050 kg/ha）.