Correlation of Leaf Area Index with Canopy Reflectance Spectrum of Flue-cured Tobacco Under Different Nitrogen Application Rate

To confirm the effects of different nitrogen application rate on leaf area index(LAI) and canopy reflectance spectrum of flue-cured tobacco,the canopy reflectance spectrum and LAI in spherical plant stage,fa st growing stage and topping stage were determined,and the correlation between them was analyzed.The results showed that:within a certain range of nitrogen application rates,LAI was promoted obviously with the increase of nitrogen fertilizer application rate during the three growing stages,while the promotion effect in topping stage was not as obvious as in the other two stages;the reflection in visible band decreased and the reflection in near infrared band increased with the increase of nitrogen application rate within a certain range;in visible light band,LAI extremely significantly negatively correlated with the reflectivity at 500,550,600,650 and 670nm;in near-infrared band,LAI significantly positively correlated with the reflectivity at 780 and 800nm,extremely significantly positively correlated with the reflectivity at 1050 and 1100nm;the vegetation index,which strongly correlated with LAI,was NDVI(1050,550).The regression model established based on that showed better prediction effect.