The Vertical Light Distribution Within Wheat Canopy And Relationship With Grain Yield Based On Radiative Transfer Process

Canopy vertical structure varies with plant height,meanwhile selective radiation is absorbed by pigment with the changes of band,so the absorption ability of radiation changes with the wavelength or plant height.However,most of the present researches regard canopy as whole,or discuss the absorption and utilization of photosynthetic active radiation,which neglect the affect of vertical structure and photosynthetic pigment.So it is significant to consider the vertical distribution of the wheat and the relationship between different light absorption and grain yield.Wheat field experiment of different planting density and nitrogen levels were proposed.Measure the phytometrical parameters(PAR),growth parameters,upward radiation and downward radiation,meteorological factors and canopy reflectance of wheat canopy at the main growth period.The experimental data were considered to analyse vertical structure in wheat.Based on the mechanism model,associated with the hyperspectral remote sensing,try to simulate parameters which are difficult to obtain of model by vegetation indices to simulate the distribution of light within wheat canopy.At first,analyze the vertical structure of wheat,with the downward cumulative leaf layer increased,leaf area index(LAI),leaf dry weight and leaf nitrogen accumulation is growing.The cumulative leaf layer changes with the growth period of increased first and then decreased,reached the maximum at booting heading stage.However,leaf nitrogen content began to reduction with the leaf layer increasing,which indicates that upper layer of the canopy contain more nitrogen.Based on Logistic model and Campbell ellipsoidal distribution model,combined with the hyperspectral remote sensing,fit parameters which is difficult to be obtained of model by vegetation indices,this research aim to simulate the variation of leaf area index of wheat canopy with relative depth distribution and ellipsoidal leaf angle distribution.For wheat canopy LAI,the simulation and prediction of RRMSE of the model was 19.26%in the whole growth period.When the relative depth of h(defined as,the proportion of the vertical distance from the top of the canopy to specific depth,accounted the whole canopy)were at 1/3,1/2,2/3,simulation and prediction of RRMSE were 15.83%,10.65%,13.89%,respectively and canopy ellipsoidal leaf angle distribution ELADP prediction of RRMSE is 19.37%.Secondly,based on the analysis of the data within the canopy radiation,transmittance decreases with plant growth,and the difference between different bands of light transmittance and light interception decreases with the growth period,the transmittance variation range of erectophile is greater than planophile.In this study,based on the classic Bill Lambert Theorem(Beer's Law),combined the hyperspectral remote sensing,using remote sensing vegetation indices to fit extinction coefficient of different band,realized the space-time dynamic simulation of different relative depths of different light qualities interception rate in wheat canopy.Throughout the growth period,when h were 1/3,1/2,2/3 and 1,the RRMSE were 24.6%,18.91%,15.16%and 15.4%,which showing the prediction accuracy of the model;the RRMSE of the model of different band,Blue RRMSE was 13.99%,14.67%for green RRMSE,red RRMSE was 14.22%.Finally,analyze the relationship between interception and dry matter accumulation and grain yield in different growth periods and different light quality,and ultimately dry matter accumulation and grain yield forecast.Throughout the growth period,when forecast dry matter accumulation from tilling to maturity by intercepted of blue,and RRMSE was 12.78%;When forecast the yield by blue light interception rate,and RRMSE was 16.9%;when forecast the yield by green light to the amount of intercepted at heading to flowering,RRMSE was 16.28%.The model can simulate canopy interception rate of different light qualities of different heights at different periods.The use of blue interception rate to forecast dry matter accumulation and the use of green interceptions to forecast grain yield are better results,the results can provid technical support for the wheat productivity assessments.