The Canopy Spectrum Characteristic Of Northeast Spring Corn And Nitrogen Nutrition Diagnosis Research

Corn production occupies an important place in the national economy in our country, so how to make the corn high yield, high quality and high benefit is an important subject in front of the current agricultural scientific workers. There is a widespread phenomenon that the use of nitrogen fertilizer in the process of corn production is unreasonable, the amount of nitrogen fertilizer increase year by year, while the utilization rate is generally low, and pollute ecological environment of the corn field seriously. In order to control the situation of total nitrogen of the corn field real time, and optimize the use of nitrogenous fertilizer of the northeast spring corn. In this paper, we adapt the method of field experiment and indoor analysis in combination, using ASD FieldSpec spectrometer of measuring scanning spectral reflectance of the corn canopy of different maize varieties under different nitrogen application levels(N1~N6), and different growing periods. To clear about the spectral response and the best wavelength of the sensitive area of the canopy leaves, we established the forecast model of detecting the spectrum parameters of the nitrogen content,and inverse the nitrogen content of the leaves by using the optimized NDVI index. The results will provide a new method for the nitrogen nutrition of the northeast spring corn based on nondestructive testing, and provide data support to develop that low cost, high precision spectral sensor of the field. The main research results as follows:(1) Nitrogen content of the corn plant and the leaf decreases gradually during whole growing period. The nitrogen content of the plant at the jointing stage and nitrogen content of leaves, nitrogen fertilizer rate at silking stage presents the secondary curve equation. At the bell stage and filling stage,the chlorophyll content of the leaf both show the tendency of twin peaks. At the bell stage, the content of chlorophyll and nitrogen fertilizer rate present exponential curve, and they have reached significant level.(2)The canopy spectral reflectance of northeast spring corn presents downtrend in the visible light region with the increase of nitrogen fertilizer rate, rise in the infrared spectrum area; At the silking stage, spectral reflectance in the determination of band is significantly higher than that at the bell stage; Under the same conditions, different maize varieties corn has different canopy spectral reflectance; Under the normal nitrogen application rate and decrease nitrogen application rate conditions, the spectral reflectivity clustering analysis of 12 corn varieties reflect the different degrees of clustering。(3)At the bell stage and silking stage, the spectral reflectance and the first derivative of the canopy leaves and the content of plant nitrogen, leaf nitrogen and chlorophyll of the northeast spring corn present negative correlation in the visible light region. There are two peaks of correlation coefficients in the visible light range, correlation coefficients in the infrared spectral region are positively correlated with that in the far infrared. The sensitive spectral bands of nitrogen plant, leaf nitrogen and chlorophyll are mainly concentrated in the green light, red light and near infrared region; The index of nutrition content of corn has little effect on the corn canopy near infrared spectral reflectance, The construction of the sensitive spectral bands provides theory basis for the model of corn nitrogen nutrition spectral index prediction.(4)Respectively, to build the model of corn nitrogen(x) at bell stage and silking stage and its spectrum index(y) prediction in the northeast spring corn. In order to determine the best index of spectral prediction of corn nitrogen content at different stages, the spectral index of plant nitrogen content at the bell stage in ratio vegetation indexR760-R718 and(R765-R548)/(R765+R548), the precision prediction and accuracy of normalized difference vegetation index(R765-R548)/(R765+R548) is higher than others at the silking stage; In the spectral index of leaf nitrogen content, ratio vegetation index(R715-R548) has higher prediction precision and accuracy at silking stage and bell stage, it can be used for inversion of corn leaf nitrogen content. And it provides theory basis for spectroscopic diagnosis of canopy nitrogen nutrition.(5)Respectively, to build the estimate model of the chlorophyll(x) and its spectrum index(y) at bell stage and silking stage of northeast spring corn. Determined the optimum spectral prediction index of corn chlorophyll; In the spectral index of chlorophyll content,difference vegetation index R749 / R712 and normalized difference vegetation index(R749- R551)/(R749 + R551) and of normalized difference vegetation index(R755- R711)/(R755 + R711) have highest precision and accuracy at bell stage and silking stage. And it can be used for inversion of corn leaf chlorophyll content.(6)NDVI measurements and calculation of NDVI value increased with the increase of nitrogen application rate, both can be used for inversion of corn leaf nitrogen content, NDVI measurements inverse correlation between nitrogen content of blade is less than the calculated value of NDVI; The spectrum reflectance maximum of the Near infrared band and the spectral reflectance minimum of the red band build optimization NDVI value associated with the significant NDVI measurements. It has significant linear correlation with corn leaf nitrogen content, it can inverse the corn leaf nitrogen content at bell stage better; 780 nm and 670 nm wavelength and 850 nm and 660 nm wavelength build the NDVI value associated with a significant NDVI measurements, it has significant linear correlation with corn leaf nitrogen content. It can phase inverse corn leaf nitrogen content at bell stage better. And it provides data support to develop a low cost, high precision of the field spectral sensor.