Rice Population Characteristics And Its Spectral Diagnosis And Application Under Different Nitrogen Levels

Through the rice nitrogen gradient test,combined with spectral technology to establish the quantitative relationship between agronomic parameters and vegetation indices,so as to realize the rapid diagnosis and real-time monitoring of crop growth and nitrogen nutrition information using spectral.This experiment is based on the field experiment research,using crop cultivation and other disciplines of knowledge,systematic analyzing the rice population characteristics and the relationship between leaf area index,leaf nitrogen accumulation,leaf dry weight,above-ground dry matter accumulation and vegetation index under different nitrogen application levels,building estimation model of rice agronomic parameters based on different varieties and different nitrogen application rate,selecting the optimal model through the test of the model,accurately estimating the amount of fertilizer to guide the field of precision fertilization according to the model.The main results summarized as follows:1.The yield and leaf area index were different among different nitrogen treatments,the yield of Yongyou 538 and Zhendao 18 was the highest,respectively 890.49kg/mu and655.84kg/mu in the amount of nitrogen was 21kg/mu（N3）,the leaf area index at different growth stages were higher than other treatments under this level of fertilization,the leaf area index of Yongyou 538 reached the biggest at booting stage was 12,the maximum value of leaf area index of Zhendao 18 reached 7.9 in the heading stage.The nitrogen application level of the two varieties within a certain range（N0-N3 treatment）,net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）and intercellular CO₂ concentration（Ci）increased with the increase of nitrogen application rate,but when nitrogen application rate increased to N4 treatment,the photosynthetic parameters were decreased in different degrees.The fluorescence parameters and photosynthetic parameters showed a similar pattern,the maximal photochemical efficiency（Fv/Fm）and photosynthetic electron transport rate（ETR）of N3 was the largest,while N1 and N0 was the lowest.2.The normalized differential vegetation index（NDVI）and the ratio of vegetation index（RVI）of rice increased significantly with the advancing of growth period from tillering stage to heading stage.NDVI and RVI showed an increasing trend with the increase of nitrogen application rate in different nitrogen application treatments,but when the amount of nitrogen fertilizer increased to N2 level,the NDVI and RVI parameter values decreased and tended to be stable.Correlation analysis showed that NDVI and RVI3.values were significantly correlated with yield from tillering stage to booting stage（P<0.01）,but there was a big difference between cultivars.Normalized difference vegetation index and ratio vegetation index of Yongyou 538 were significantly correlated with yield at jointing and heading stage,while normalized difference vegetation index and ratio vegetation index of Zhengdao 18 and yield were significantly related in tillering and booting stage.4.The correlation coefficient of leaf area index with RVI and NDVI reached more than0.8.The relativity between the predicted values and the measured values is more than0.8,and RMSE were less than 1.5,and RE was below 0.25.The correlation coefficients of leaf nitrogen accumulation with NDVI and RVI were 0.79 and 0.81 respectively,the correlation between the predicted values and the measured values were 0.62 and 0.29respectively.The correlation coefficient of leaf dry weight with NDVI and RVI were more than 0.84,the correlation between predicted values and measured values of NDVI and RVI models were 0.49 and 0.39 respectively.The correlation coefficient of above-ground dry matter accumulation and NDVI,RVI were 0.73 and 0.80,the correlation between the predicted values and the measured values were 0.19 and 0.13 respectively.The comprehensive analysis shows that the optimal model is based on the linear model of NDVI and leaf area index,namely LAI=24.694NDVI-2.3481（S-R²=0.823,P-R²=0.839）and a linear model based on RVI and leaf area index,namely LAI=6.4446RVI-7.3007（S-R²=0.862,P-R²=0.819）.4.Based on the results of this study,a linear model based on NDVI and leaf area index is established（LAI=24.694NDVI-2.348）,using canopy spectra at jointing stage monitor rice leaf area index,then determining the strategy of nitrogen application at jointing stage according to the recommended model of nitrogen fertilizer that has been constructed.The results showed that yield level increased 40-90kg/mu than the traditional high-yield cultivation nitrogen mode,and nitrogen use efficiency increased by 4-50%under the recommended fertilization mode.