分析了在正常、 偏低、 偏高等不同施氮水平下, 玉米生长期冠层反射光谱与叶绿素含量的相关关系, 结果表明玉米叶绿素含量检测的敏感期为拔节期和喇叭口期。 正常施氮水平下玉米冠层光谱反射率与叶绿素含量相关关系高于其他施氮水平, 即r正常>r偏高>r偏低。 整个生长期由苗期开始二者相关系数绝对值满足先上升后下降, 于开花吐丝期达最低后回升的趋势, 其中玉米拔节期和灌浆期冠层反射光谱与叶绿素含量呈正相关。 选取558, 667, 714和912 nm, 分别对玉米拔节期和喇叭口期建立了MLR和PLSR检测模型, 经比较, 虽然PLSR模型复相关系数较MLR模型有所降低, 但模型鲁棒性得到增强。 分析拔节期和喇叭口期各种植被指数与叶绿素含量的相关关系, 表明DVI优于其他指数, 且拔节期DVI与叶绿素含量呈二项式相关, 喇叭口期二者呈指数相关。

The canopy spectral reflectance and chlorophyll content of corn were measured and analyzed under different nitrogen treatments. The correlation between spectral reflectance and chlorophyll content was discussed based on different growth stages and different nitrogen levels. The results showed positive correlations under high and normal nitrogen treatment, while negative correlation under low nitrogen treatment. The relation between reflectance of normal fertilizer region and chlorophyll content was better than others, with rNormal＞rHigh＞rLow. Normal fertilizer was the best condition to detect the corn chlorophyll content using spectral reflectance. Analysis of the relations at different growth stages showed that on the band of 400-1 000 nm the absolute value of correlation coefficient increased and reached the maximum at shooting stage, it decreased until anthesis-silking stage, and then rebounded at milking stage. The positive correlations were found at shooting and milking stage, while negative correlations were found at seedling, trumpet and anthesis-silking stage. It was indicated that the sensitive stages to detect the chlorophyll content were shooting and trumpet stage with high absolute value of correlation coefficient above 0.6 around 550 nm. In order to detect the chlorophyll content of corn, 558, 667, 714 and 912 nm were selected to establish the MLR model and PLSR model. The results showed that PLSR was more capable of building chlorophyll content models reflecting correct relations among multi-variables compared with MLR. In the meanwhile, three wavelengths were selected (558, 667 and 714 nm) to build different vegetation indices such as GDVI, GRVI, GNDVI, DVI, RVI and NDVI. The correlation between DVI and chlorophyll content was better than others and DVI was used to establish binomial model and exponential model at shooting stage (R2=0.80) and trumpet stage (R2=0.66) respectively which was higher than PLSR. It also provided a feasible method to detect chlorophyll content non-destructively.