Diagnosis Of Nitrogen Nutrition In Summer Maize Based On Hyperspectral And Simulated Multispectral Data

The study was carried out in Daxing Experimental Research Base of Beijing Engineering and Technology Research Center of State Water-Saving Irrigation from June to September in 2017 and 2018.Small-scale evapotranspiration test and field plot test were carried out with summer maize as the object of study.In this study,small-scale lysimeter experiment was carried out to examine the characteristics of canopy spectral reflectance variation of summer maize under different fertilization levels.The relationship between canopy spectral reflectance and nitrogen content was investigated,based on which sensitive bands for the maize canopy nitrogen monitoring was selected and a suitable spectral index model was determined,and the hyperspectral estimation model of nitrogen content in summer maize canopy was established.At the same time,based on the measured hyperspectral information of summer maize canopy,the spectral reflectivity of landsat8-OLI and GF-1 satellite sensors was simulated by using the spectral response function of the sensor.The estimation model of canopy nitrogen content based on sensitive broad-band spectral index and multi-band spectral index was constructed.The results suggest that:(1)In the visible light band,the canopy spectral reflectance of summer maize decreased gradually from jointing stage to male-heading stage,and increased gradually from filling stage to mature stage.In the near infrared band,the variation trend is opposite to that in the visible band.Under different fertilization levels,the canopy of summer maize decreased with the increase of nitrogen application rate in the visible light band,and increased with the increase of nitrogen application rate in the near infrared band,and in the near infrared band,the canopy of summer maize decreased with the increase of nitrogen application rate..(2)At jointing stage,heading stage,filling stage,mature stage and whole growth stage,the sensitive bands for monitoring nitrogen content in summer maize canopy by spectral reflectance were 685 nm,937 nm,774 nm,719 nm,762 nm,The sensitive bands measured by the first derivative of reflectivity are 737 nm,752 nm,738 nm,715 nn and 726 nm,respectively.The most suitable spectral indices are ND(FD730,FD525),mNDVI,(SDr-SDb)/(SDr SDb)and NDRE,respectively.And the simulation accuracy of the nitrogen content prediction model based on the three models is spectral index,first derivative of spectral reflectivity and spectral reflectivity from high to low.(3)Based on the inversion of simulated spectral reflectivity(1/R)and near infrared band central wavelength 864nm reflectivity and nitrogen content in summer maize canopy during the whole growth period,it is suitable for estimating the nitrogen content in summer jade canopy during the whole growth period.The accuracy of the model is tested.The determination coefficients were 0.621 and 0.613,respectively.Based on 10 multi-band spectral indices and plant nitrogen content calculated by principal component analysis(PCA),10 multi-band spectral indices and plant nitrogen content were calculated in summer maize during the whole growth stage.The model's decision coefficient R2was 0.692,and the simulation accuracy was high.(4)Based on the reciprocal reflectivity of sensitive wide band,central wavelength and multi-band spectral index,the estimation model of nitrogen content in summer maize plants during the whole growing period was constructed.According to the simulation accuracy of the model,multi-band spectral index was in order from high to low.Sensitive band reflectivity reciprocal,central wavelength.