Grain Yield And Morpho-physiological Responses Of Increased Maize Plant Density And Modelling Studies

Huang-Huai-Hai region is one of the major grain-producing areas in China.The high and stable yield of maize in this region is of great significance to China’s food security.At present,under the background of rapid increase of population and continuous decrease of arable land area,it is particularly important to meet people’s food demand by increasing the yield per unit area.Moderate density planting is one of the important topics of maize production in the future.However,the increase of planting density will affect development and population morphogenesis of maize.Particularly,maize canopy morphology and physiological ecology are highly dependent on planting density.Canopy morphological structure and physiological ecology are the basis for the establishment of corn seeds.Therefore,it is of great practical significance to study the regulation mechanism of abortion caused by high plant density and the characteristics of canopy morphology structure and function for high plant density tolerant maize cultivars.With the help of plant morphological functional-structural model,plant ideotype parameters suitable for high plant density can be extracted effectively.By adjusting the parameters of the model,the photosynthetic productivity of maize under different conditions will be simulated,which provides a new idea for the plant ideotype design suitable for high plant density.In this thesis,field experiments were carried out in investigating the response of maize morphology and physiology to increased plant density,and based on the experiments,to characterize maize morphological response to increased plant density.Three different plant hybries i.e.Zhengdan 958,Lonping 206 and Jinqiu 119 with different canopy architecture,field experiments were conducted in Mengcheng,Anhui Province,from 2016 to 2018,in which,five planting densities,i.e.45,000,60,000,75,000,90,000 and 150,000 plants hm-2(referred to as PD4.5,PD6,PD7.5,PD9 and PD 15 respectively)with three replicates were designed.grain number and weight of top,middle and base of ear in maize varieties under different planting densities were measured.Maize canopy morphological and photosynthetic characteristics under different planting densities have been investigated.The relationship between canopy morphology and increased plant density was quantified with linear functions.ADEL-Maize model has been revised by introducing the relationship,and thus the simulation of the effect of density increase on the morphological structure was realized.The key research results are as follows:(i)With the increase of plant density,corn yield first increases and then decreases.There were differences between varieties in the relative optimized planting density.The suitable planting density of Zhengdan 958 and Longping 206 was 75,000 plants hm-2,and that of Jinqiu 119 was 60,000 plants hm-2.The decrease in yield was mainly due to the decrease in the number of grains and the 100-grain weight in the top part of ear.(ii)With the increase of plant density,the leaf length and leaf sheath length in lower phytomers increased,the leaf length and sheath length in upper phytomers decreased,the leaf width and leaf sheath width in whole plant decreased,and the internode length and internode diameter in whole plant decreased.The light transmittance in the ear layer and the bottom layer of maize population decreased with the increase of plant density.The light transmittance of each canopy layer of the leaf-upright maize varieties was higher than that of the semi-compact maize varieties.(iii)Based on the field experiment data in 2016,the relations between the changes of organ sizes(leaf length,leaf width,leaf sheath length,leaf sheath width,internode length and internode diameter)in different parts of the canopy of Zhengdan 958 and the increase of planting density were established,and these relations were introduced into the ADEL-Maize model.In the year of 2018,the revised ADEL-Maize model was applied in simulating maize canopy morphology in flowering stage for different plant densities,and the simulation has been independently validated using the c data measured in 2018.The results showed that the response relation of morphology and plant density found in this study was reliable.In summary,in this study,it was found that the number of grains per ear and the grain weight were affected by increasing plant density,among them,the number of grains per ear was more sensitive to high plant density.It was shown that the top part of an ear was easy to be aborted.In addition,this study also improved the ADEL-Maize model and realized the simulation of maize canopy morphology under different plant density,so as to provide assistance in exploring how to improve the canopy photosynthetic capacity under high paint density based on the model assistance.