基于冠层反射光谱的夏玉米叶片碳氮比监测

基于不同夏玉米品种在2个年份不同施氮水平下的田间试验,研究夏玉米叶片碳氮比随生育期的变化模式及其与冠层反射光谱的定量关系,建立玉米叶片碳氮比的定量监测模型。结果表明,夏玉米叶片碳氮比随施氮量的增加而降低,随生育进程呈"高-低-高"动态变化趋势。利用冠层反射光谱监测叶片碳氮比的适宜时期为孕穗期至吐丝期。13个光谱参数与2个品种叶片碳氮比有较好的相关性。通过比较模型的拟合决定系数(R2)和预测标准误(SE),确定转换型植被指数(TVI)与叶片碳氮比的线性回归方程为最佳监测模型。经不同年际独立试验数据的检验,叶片碳氮比监测模型的预测精确,相关系数(r)为0.682 4,根均方差(RMSE)为0.405 2,表明夏玉米冠层反射光谱可用来定量估测叶片碳氮比的变化状况。

Monitoring of the Carbon to Nitrogen Ratio in Summer Maize Leaves with Canopy Reflectance Spectra

Two field experiments were conducted with different maize cultivars and nitrogen levels across two growing seasons, and time-course measurements were taken on canopy spectral reflectance and leaf carbon to nitrogen ratio during the period of experiment. The results showed that the carbon to nitrogen ratio in maize leaves decreased with increasing nitrogen rates, taking on the trends of high-low-high pattern with growth stages. The proper time for monitoring leaf carbon to nitrogen ratio should be from booting to silking stage. C/N ratio in maize leaves ratio was highly correlated to thirteen spectral parameters among all cultivars and three growth stages. After comparing the R2 and SE of regression equations, the spectral index of TVI was found to be the best parameter for predicting C/N ratio in maize leaves. Testing of the monitoring models with independent dataset indicated that the predictive precision(r) was 0.682 4, and RMSE was 0.405 2. It was concluded that the present spectral model was feasible and reliable for estimating C/N ratio of maize leaves with different cultivars and nitrogen leaves.