Monitoring Growth Characteristics And Evaluating Productivity Based On Canopy Spatial Differences In Winter Wheat

Developing a rapid and accurate method for monitoring growth status andevaluating productivity is the urgent demand for modern agriculture,which would provide useful measurements for field management and help the government make proper policies.The spatial differences occurred generally in wheat canopy,mainly including the different photosynthetic characteristic at different leaf positions and the uneven distribution of photosynthetically active radiation?PAR?.Carrying out the researches based on the spatial differences in wheat canopy so as to monitor growth status and evaluate productivity is of significance,because it could improve filed management technology and manufacturing competitiveness.The purpose of this study was to analyse the photosynthetic characteristic at different leaf positions and light distribution in wheat canopy,on the basis of different years,varieties,irrigation and nitrogen treatments.In the following,the spatial differences and its relationships with growth characteristics and productivity were anlysed.The anticipated results would provide guidance and technical support for wheat management.Firstly,the paper analysed the changes of net photosynthetic rate?Pn?andchlorophyll fluorescence?Chl F?parameters at different growth stages and leaf positions under different varieties and nitrogen application,and illuminated the relationships between Pn and Chl F parameters aimed at evaluating biomass and grain yield in winter wheat using Pn and Chl F parameters.The results showed that Pn and Fv/Fo increased then decreased with growth in both cultivars,but Fm'and Fv'/Fm'showed a different trend,decreasing gradually from jointing to late-filling stage.Leaf Pn decreased significantly with decreasing leaf position.In contrast,Fm',Fv'/Fm'and Fv/Fo increased then decreased with decreasing leaf position.Correlation coefficients?r?were much higher between the light-adapted parameters and Pn,in terms of leaf positions,correlation coefficients were in the order of L1>L2>L3>L4.Plant biomass was significantly correlated with the Pn accumulation of L1-4,with Pn accumulation at the booting to initial-filling stage forming a better index of final biomass.The Fm'accumulation of L12 showed better correlation with biomass?determination coefficient:R²=0.826?and grain yield?R²=0.755?at initial-filling stages.Overall,for different varieties and nitrogen treatments,Fm'accumulation of L12 during booting and initial-filling could be used as an accurate index of wheat biomass and yield.The wheat canopy was divided into different points across horizontal and vertical directions,the spatial distribution of PAR and its relationships with growth were analysed.The results showed that,in the horizontal direction,the more close to the main stem the more the Ir was,the more close to row the less the Ir was.In vertical direction,the Ir decreased with increasing height.Leaf nitrogen content?LNC?maintained higher values at booting-heading stages,then decreased.Leaf area index?LAI?presented a unimodal trend at different growth stages.Spatial difference index of the bottom layer(PAR_1-3)showed a better correlation with LNC,but there were large differences between growth stages.However,the better correlation was occurred not only at different growth stages but also for combined growth period?booting to mid-filling?,while it was feasible to use unified linear regression equation for evaluating LAI.The results showed that the correlation between PAR_1-3and a new index?LANI?performed better than that of LNC and LAI,because the LANI combined the information of leaf area and leaf nitrogen content.Light radiation is the material basis of crop growth,and the amount of interceptedlight radiation in the canopy is of great significance to the biomass formation.The results showed that in the vertical direction the accumulation of PAR interception at the bottom were higher than that of the top.In the horizontal direction,the more close to the main stem the more the accumulation of PAR interception was,the more close to row the less the accumulation of PAR interception was.The accumulation of PAR interception at the bottom and the middle row showed better correlations with yield,grain weight and grain numbers per spike,while the accumulation of PAR interception at the bottom(APAR₁₂₃)performing the best.For different growth stages,there was a significant difference in correlations.In terms of biomass,correlation coefficient between APAR₁₂₃?Jointing-Maturity?and biomass was 0.752,correlation coefficient between APAR₁₂₃?Jointing-Anthesis?and increased biomass?Jointing-Anthesis?was 0.806,Moreover,APAR₁₂₃?Anthesis-Maturity?and increased biomass?Anthesis-Maturity?showed a lower correlation?r=0.694?.In conclusion,APAR₁₂₃could be used to evaluate grain yield and biomass,which would provide useful information for strengthening field management and regulation in the key growth stage of wheat.In conclusion,the photosynthetic characteristic of leaves and spatial distribution oflight had close relationship with wheat growth,and it could be used as a real-time and fast method for monitoring wheat growth status and evaluating productivity,which would provide technical references and theoretical basis for precise agriculture.