Study On Critical Nitrogen Concentration Dilution And Spectral Index Models Of Rice In Yangtze River Reaches

Nitrogen being one of the most important plant nutrients influences all aspects of crop growth and development,shaping yield throughout the growing season.N has a significant influence on crop yield and quality formation.The crop nitrogen nutrition diagnosis and precise regulation is an integral part of digital and precision agriculture.Multi-locational field experiments using different rice cultivars as experiment material along with varied nitrogen application rate were carried out in different years.This study was conducted to analyse the dynamic variation in characteristic of canopy spectral vegetation index and nitrogen concentration in rice systematically.Based on spectral vegetation index and relative days after rice transplanting,the plant critical nitrogen concentration,nitrogen nutrition index and relative spectral index models were constructed for nitrogen nutrition diagnosis and regulation in rice to develop effective diagnostic tool and theoretical basis.First of all,this study was aimed to couple modern remote sensing based spectral index with agronomic indicators for monitoring crop growth and development.The rice canopy spectral index critical nitrogen concentration and nitrogen nutrition index models in different eco-types of rice(Japonica and Indica)were developed according to the methodology proposed by Justes.The critical nitrogen dilution models of Japonica and Indica rice were described by the equations,Japonica:Nc =1.7628NDVI-0.283 and Indica,Nc=1.6194NDVI1.6194,respectively.The covariance analysis showed that the model of Japonica and Indica rice were significantly different due to regional and climatic factors.The nitrogen nutrition index model was then constructed on the basis of critical nitrogen concentration,the results showed that the values nitrogen nutrition index were greater than 1 and lower than 1 under non-limiting and limiting N conditions,while the value of nitrogen nutrition index under appropriate nitrogen nutrition was around 1.Moreover,this study explored that the relationship between the amount of nitrogen topdressing and nitrogen nutrition index had good linear relationship,can use the blank nitrogen treatment of nitrogen nutrition index to estimate the difference between the later period of nitrogen.Therefore,the research was focused to develop a model of critical nitrogen concentration and nitrogen nutrition index model for in-season assessment of rice nitrogen nutrition diagnosis and precise estimation of nitrogen requirement for late rice.Then,we analyzed the data of leaf area index(LAI),aboveground plant dry matter,canopy vegetation index(NDVI),and grain yield.The quantitative relationships were established based on normalized data processing and modeling method between NDVI,agronomic index and relative days after transplanting,etc.The robust correlation was found between the canopy NDVI of aboveground plant dry matter and leaf area index.Then,relative NDVI dynamic model:y =(1 + e-21.8012x(x-0.1582))-1-(1+e-7.2921×(x-1.0522))-1,R2=0.9229 was constructed for different eco-types of rice.The model can accurately predict the NDVI index dynamic for entire crop growth period of high-yielding rice groups.At the same time,considering the influence of cultivars,we have also developed the relative NDVI dynamic model of Japonica and Indica rice,the accuracy of the model were(k,0.9986,0.9958),(R2= 0.9748**,0.9283**).The relative NDVI dynamic model developed in present study can accurately reflect the population dynamics,crop condition and predict crop yields for high-yielding rice cultivars and can also be used as a rapid and accurate method for monitoring and diagnosis nitrogen nutrition.