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THE HIGHEST POPULATION PRODUCTIVITY OF N FERTILIZATION AND ITS FORMATION CHARACTERISTICS ON JAPONICA SUPER RICE IN SOUTH CHINA

GONG Jin-long HU Ya-jie GE Meng-jie LONG Hou-yuan CHANG Yong MA Qun YANG Xiong ZHANG Hong-cheng DAI Qi-gen HUO Zhong-yang XU Ke WEI Hai-yan(Agronomy College of Yangzhou University/Innovation Center of Rice Cultivation Technology in the Yangtze Valley, Ministry of Agriculture/Key Laboratory of Crop Genetics and Physiology of Jiangsu Province,Yangzhou University,Yangzhou,Jiangsu 225009)  
A field experiment was conducted using five japonica super rice cultivars in south China(Nanjing44,Ningjin1,Ningjing3,Yangjing4038,Wujing15) as materials and a conventional japonica rice cultivar Wuyunjing7 which had the same growing period as CK to achieve the highest productivity of all cultivars under seven nitrogen fertilization levels(0,150.0,187.5,225.0,262.5,300.0,337.5kg·hm-2).Meanwhile,the grain yield and its components,dynamics of population stems and tillers,leaf area index,dry matter weight,root-shoot ratio and weight of dry matter of root,plant type,lodging characteristics were studied systematically.Results showed that the highest population productivity of N fertilization in super rice was 10.51(10.30~10.68) t·hm-2,significantly higher than CK(9.77~9.82t·hm-2),with the increasing range of 5.2%~8.7%.Compared with CK,more panicles per unit area,spikelets per panicle and population spikelets(42442.11~44873.23×104·hm-2) were observed under the highest population productivity of N fertilization in super rice,with the roughly same level of seed-setting rate and 103-grain weight.In comparison with CK,number of stems and tillers rose faster to a suitable case with super rice at the highest population productivity of N fertilization,slightly higher than expected number of panicles at the critical leaf-age for productive tillers stage,and then increased slowly to the peak with an appropriate number(1.4~1.5 folds of expected panicle number).After that,it decreased gently and ultimately arrived at a significantly higher rate of productive tillers/total tillers(66.9%~70.4%).Dynamics of leaf area index at the highest population productivity of N fertilization in super rice developed the same tendency as dynamics of population stems and tillers,and the maximal leaf area index(7.72~7.97) appeared at the booting stage,and then decreased stably to a high level of 3.30~3.74 at maturity stage.As for the dry matter accumulation,the highest population productivity of N fertilization in super rice showed more advantages than CK from transplanting to critical leaf-age for productive tillers and lower accumulation from critical leaf-age for productive tillers to jointing,and then accumulated fast to 10.80~11.08t·hm-2 at heading stage and 17.58~18.29t·hm-2 at maturity stage(6.78~7.22t·hm-2 from heading to maturity),significantly higher than CK.Root-shoot ratio and weight of dry matter of root at the highest population productivity of N fertilization in super rice were significantly higher than CK.As the advancement of growth and development stage,the advantages went larger and larger,additionally with strong activity(root exudates 3.53~3.74g·m-2·h-1 from heading to waxy stage) at the later period.The formation characteristics were as follows.Firstly,low leaf position tillers came out quickly on the basis of high seedling quality so that panicles increased stably at the precise population starting point.Secondly,source coordinated with sink smoothly with the help of high ratio of leaf area of productive tillers and ratio of leaf area from flag leaf to 3rd leaf,as well as straight and erect plant type,in the context of high dry matter accumulation and leaf area.Finally,grain-filling layer of high use efficiency of solar energy was supported by large output of stems and sheaths,high second weightening and strong root.At the highest population productivity of N fertilization,due to possessing more panicles,spikelets per panicle,population spikelets,N uptake and grain yield,super rice was suitable for mechanical transplanting based on owning strong photosynthetic production capacity and large total filling,improved plant type and strong resistance lodging.
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