Objective Application of nitrification inhibitor and/or biochar for fertilization with reduced nitrogen was evaluated against the effects on carbon and nitrogen metabolisms, nitrogen utilization, and quality of flue-cured tobacco.

Method ‘Yunyan 87’ tobacco plants were grown on lots applied conventional fertilization (CK) or with the addition of 3,4-dimethylpyrazole phosphate (nitrification inhibitor, DMPP) (T1), biochar and DMPP (T2) or biochar, DMPP, and 20% reduction on nitrogen (T3). Products and enzymes related to carbon and nitrogen metabolisms, chemical composition, sensory quality, economic traits, and nitrogen utilization of leaves on the tobacco plants under treatments were monitored.

Result Compared to CK, the treatments raised the total and reducing sugar contents and neutral invertases (NI) and sucrose synthetase (SS) activities but reduced the total nitrogen and nicotine contents in the leaves. The total and reducing sugar in the samples of T3 increased in 60 d after transplanting by 68.12% and 71.59%, respectively, while the total nitrogen and nicotine decreased in 90 d by 26.62% and 24.78%. respectively. The GS activities were significantly 80.06% higher for T2 and 69.12% for T3, and the nitrogen use efficiency 73.45% higher for T1, 77.93% for T2, and 43.97% for T3. The chemical balance, sensory quality, and economic traits of the leaves were also improved, as shown by the highest comprehensive scores on upper and middle leaves under T3, a yield of 48.43%, an output of 65.80%, and the 11.70% higher average price than CK.

Conclusion By applying DMPP and biochar for fertilization, the carbon and nitrogen metabolisms of tobacco plants could be optimally regulated to effectively utilize the available nitrogen in soil. A 20% reduction on nitrogen for fertilization would still provide the soil with appropriate fertility to deliver high-quality flue-cured tobacco leaves.