关中地区小麦冠层光谱与氮素的定量关系

Quantitative relationship between wheat canopy spectrum and nitrogen in Guanzhong area

【目的】分析不同生育期及整个生育期小麦叶片氮含量（LNC）与冠层光谱反射特征的关系,以实现对田间小麦活体氮素营养状况的监测,为小麦叶片氮素状况的精确诊断提供依据。【方法】以位于陕西关中地区杨凌揉谷镇、扶风马席村和巨良农场的3个小麦试验田为研究对象,测定不同长势及生育期小麦LNC及冠层光谱反射率,分析不同长势下小麦LNC和反射率的变化,并研究氮含量与冠层光谱反射率的相关性,以及小麦LNC与比值植被指数（RVI）、归一化植被指数（NDVI）的相关性,建立小麦LNC的敏感波段及光谱监测模型。【结果】在同一生育期,长势差的小麦叶片氮含量较低,长势较好的叶片氮含量高。与单波段相比,组合波段构成的植被指数RVI、NDVI与LNC的相关性明显提高,近红外波段（730~1 075nm）和红波段630,660,690nm组成组合波段的RVI、NDVI与LNC呈极显著正相关,其中LNC与RVI的相关性较高。利用独立的小麦田间试验数据,采用通用的均方根差（RMSE）、决定系数（R^2）、准确度（斜率）3个指标对所建立的模型进行检验,最终选取RVI（970,690）为监测小麦LNC的最佳光谱参数,构建的最佳模型为LNC=0.176 3×RVI（970,690）^0.775 6,R^2为0.863,RMSE为0.137,准确度为0.979,接近于1。【结论】利用小麦冠层光谱反射率构建了预测小麦LNC的最佳模型,该模型具有较好的准确度和普适性,适用于整个生育期小麦叶片氮含量的监测。

【Objective】Relationship between wheat leaf nitrogen content（LNC）and canopy spectral reflection characteristics during different growth periods and the whole growth period was analyzed to realize the monitoring of living nitrogen nutrition in field and provide basis for accurate diagnosis of wheat leaf nitrogen status.【Method】In this paper,experiments were conducted in three wheat fields located in Shaanxi Guanzhong region including Yangling Rougu,Fufeng Maxi village,and Juliang farm.Leaf nitrogen content（LNC）and canopy spectral reflectance of wheat at different growth periods and the whole growth period were measured and the changes in LNC and reflectance and correlation between them were analyzed.Ratio vegetation index（RVI）and normalized difference vegetation index（NDVI）were also investigated toestablish a monitoring model for LNC sensitive wave bands and spectrum.【Result】In same stage and different growing conditions,poor wheat leaves had lower LNC than well growing leaves.LNC had higher correlations with vegetation indexes of combined bands than with vegetation indexes of single band.RVI and NDVI of combined near infrared bands（730-1 075nm）and red bands（630,660 and 690nm）showed significantly positive correlations with LNC,and RVI showed the best relationship.Based on independent wheat field experimental data,root mean square difference（RMSE）,determination coefficient（R^2）,and accuracy（slope）were used to test the established model and RVI of R970 and R690was selected as the best parameter for predicting LNC.The quantitative equation was LNC=0.176 3×RVI（970,690）^0.775 6 with R^2 of 0.863,RMSEof 0.137 and slope of 0.979.【Conclusion】The established optimal model for forecasting wheat leaf nitrogen content（LNC）using wheat canopy spectral reflectance had good accuracy and universality and was suitable for monitoring LNC at the whole growth period.