Dynamic simulation of leaf area index of tobacco based on nitrogen effect

This study was set up to clarify the dynamic characteristics of leaf area index of flue-cured tobacco under different nitrogen levels and the relationship with accumulated temperature. The leaf area index and dynamic characteristics of three flue-cured tobacco cultivars ('YU12', 'QIN96'and'YUN87') were measured under different nitrogen levels (0 kg·hm^-2, 30 kg·hm^-2, 60 kg·hm^-2 and 90 kg·hm^-2) to improve photosynthetic structure of flue-cured tobacco. Using the Curve Expert 1.40 software and the limit method, the normalized accumulated temperature model was established. The result indicated that:1) A unimodal curve between leaf area index and accumulated temperature was observed after transplanting of flue-cured tobacco, with a skewness less than 0. Leaf area index of flue-cured tobacco increased with increasing nitrogen level, and the peak value of leaf area index was in the order of'QIN96' > 'YUN97' > 'YU12' at the same nitrogen level. 2) The rational function model y=(a+bx)/(1+cx+dx²) yielded the best simulation result of leaf area index change with relative active accumulated temperature with high precision level (R²=0.980 7^**). The accuracy and precision of the normalized model were tested with data for 2015, and the simulation accuracy (k) was all above 0.958, the precision (R²) all above 0.95 and RMSE below 6.04%. 3) There were significant differences among some varieties and nitrogen levels, showing that variety interaction with nitrogen level mainly changed the model values of b, c and d. 4) The velocity of relative leaf area index change during the growing period showed trends in'N'curve, reflecting the actual variability of leaf area index. 5) Secondary indexes were more sensitive to different nitrogen levels. The mean leaf area index and maximum leaf area index increased with increasing nitrogen level. These characteristic indexes of leaf area index could be served as a reference base for the regulation of plant nitrogen of flue-cured tobacco population. The model provided theoretical basis and decision support for monitoring growth dynamics and photosynthetic characteristics of flue-cured tobacco population.