Construction and Nutritional Diagnosis of Shoot Critical Nitrogen Dilution Curve of Flue-cured Tobacco in Shandong Tobacco Growing Region

In order to establish a critical nitrogen dilution curve for the shoot of flue-cured tobacco in the Shandong tobacco-growing areas, explore the feasibility of diagnosing nitrogen nutritional status of flue-cured tobacco using nitrogen nutrition index, and optimize nitrogen management for flue-cured tobacco, six nitrogen fertilizer application rates were set up in field to analyze their impacts on the accumulation of dry matter and nitrogen concentration in the shoot of flue-cured tobacco after transplantation. With the increased nitrogen application, the dry matter accumulation of flue-cured tobacco in each sampling period generally showed a trend of first increasing and then stable. The dry matter accumulation in the shoot of flue-cured tobacco under different fertilization treatments was significantly different. With the increase of dry matter accumulation in the shoot of flue-cured tobacco, the nitrogen concentration in the shoot of flue-cured tobacco under different fertilization treatments decreased gradually. The critical nitrogen concentration and dry matter accumulation in the shoot of flue-cured tobacco fitted the power function relationship well. The critical nitrogen dilution curve with dry matter accumulation in the shoot as the driving variable is Nc = 2.25×DM^−0.13, and its coefficient of determination R² is 0.72 (p<0.05). The nitrogen nutrient index (NNI) of different nitrogen fertilizer treatments fluctuated to a certain extent, and showed a trend of first increasing and then decreasing with the increase of transplanting days. The nitrogen nutrient index (NNI) was calculated according to the critical nitrogen dilution curve to determine the nitrogen nutrient level of flue-cured tobacco. The nitrogen nutrient level was higher when the nitrogen fertilizer application rate was 90 kg/hm². The equation of the critical nitrogen dilution curve of the shoot of flue-cured tobacco in Shandong tobacco-growing area is Nc = 2.25×DM^−0.13. The nitrogen nutrition status of flue-cured tobacco in Shandong tobacco-growing area can be evaluated by the critical nitrogen dilution curve of the shoot and the nitrogen nutrition index. The results show that the appropriate application rate of nitrogen fertilizer in this test site is about 90 kg/hm².