Effects of Exogenous Carbon Sources on Nitrogen Transformation and N₂O Emissions in Tobacco-planting Soil

In order to explore the effective measures to regulate soil nitrogen (N) content in tobacco planting soil during the late growth stage of flue-cured tobacco. An incubation experiment was conducted to study the effects of glucose, sawdust and their mixture on N transformation and N₂O emissions in tobacco planting soil. Based on the equal carbon content (3000 mg/kg) addition, the experiment included 5 treatments: G1S0, glucose: sawdust =1: 0 (Calculated by pure carbon, the same below); G2S1, glucose: sawdust=2:1; G1S1, glucose: sawdust=1:1; G1S2, glucose: sawdust=1:2; G0S1, glucose: sawdust =0:1; and no carbon added as control (CK). The results showed that the soil inorganic N content was decreased by 51.71, 61.78, 62.33 and 62.46 mg/kg in G1S0, G2S1, G1S1and G1S2 treatments respectively, but increased by 4.12 mg/kg in G0S1 treatment compared with that in CK at the first day of the incubation. The contents of soil inorganic N in G1S0, G2S1, G1S1, G1S2 and G0S1 treatments all showed increasing trends after reaching the minimum values at the 7, 14, 14, 14 and 28 days of the incubation, respectively. The soil inorganic N contents in treatments amended with exogenous carbon sources were all decreased by 96.80~148.10 mg/kg compared with that in CK at the end of the incubation. Meanwhile, the cumulative emissions of CO₂ and N₂O in all carbon sources amended treatments except for G0S1 were increased significantly (p<0.05) compared with those in CK, So, the addition of glucose, sawdust and their mixture could significantly decrease the content of soil inorganic N (p<0.05). Combined application of glucose and sawdust could accelerate and enhance the intensity of soil microbial immobilization of N compared with single application of sawdust. And it could also prolong the time of soil microbial immobilization of N compared with single application of glucose. In addition, the addition of exogenous carbon source could increase soil microbial activity and stimulate N₂O emissions simultaneously. In general, the mixed application of glucose and sawdust had the best effect on reducing the soil inorganic N content. Therefore, application of exogenous carbon source could be a useful measure to regulate soil N content in tobacco planting soil.