| Under the situation that cultivated land area and quality are continuous decline,increasing crop yield per unit area is the most important way to reduce the pressure of food demanded,due to continued population growth.To achieve high yield,excessive nitrogen fertilizer was used in recent years,which resulted in multiple negative effects.Therefore,exploring suitable cultivation measures combined with nitrogen fertilizer rate,to improve the crop use efficiency of light,temperature,water and other resources is urgently needed.In this study,field experiments were conducted during 2012-2014 on a long-term experimental station,Institute of Agricultural Science Research,Rugao City,Jiangsu Province.Split plot experiment was conducted with 5 nitrogen levels(0?90?180?270?360 kg ha-1)and two planting density[32.47 X 104 points per hectare(High density,HD)and 25.51×104 points per hectare(Low density,LD)].We mainly focused on the effects of nitrogen level and transplant density on factors about groups building;accumulation of biomass and total N;groups characteristics of physiological and ecological;the spatial variation of nutrient and substance in rice plant during grain filling,in order to provide effective theoretical and practical basis for the selection of suitable nitrogen fertilizer rate and planting density.The main results of this study are as follows:1.N level and planting density affect biomass accumulation and distribution at different growth stages.Under HD,the biomass reach to the highest when N level is N180,while under LD N level is N270.Before booting stage,biomass is generally larger under HD than under LD,subsequently,larger individuals under LD can compensate for the deficiency of groups,resulting in difference between the two groups decreased gradually.During grain yield formation process,the biomass of different sites leaf was rest leaf>top 1?top 2>top 3,biomass of different sites shoot was rest shoot>top 2>top 3 ? top 1,biomass of different sites sheath was rest sheath>top 1>top 2>top 3;Total biomass reduction of different organs was sheath>leaf>shoot.2.Under HD,rice obtain more coordinated yield components,higher total N accumulation,and their highest grain yield when N level is N180,while under LD the N level is N270,moreover,there are no significance difference between their highest grain yield;Under HD,the highest grain yield more largely depends on more panicles per unit area,while under LD its highest grain yield more largely depends on more spikelets per panicle;With N level increasing:the proportion of aboveground N accumulated during vegetative growth period is increasing,on the contrary,the proportion of reproductive growth period is decreasing,the increase amplitude of aboveground N accumulation and grain yield are both decline.Therefore,Recovery efficiency of N(REN),Agronomic efficiency of N(AEN),Partial factor productivity of N(PFPN),Physiological efficiency of N(PEN)were all decline with N level increasing,besides,there is no significant difference between LD and HD.3.For any N treatment,HD can achieve effective tillering earlier than LD,although the percentage of earbearing tiller under HD(80.9%)is less than under LD(83.7%),the effective tiller number per unit area reach to maximum when N level was N180 under HD.Taking growth characteristics of mid-tillering stage as an example,indicating that:there are significant positive relationship between relative tiller rate and the relative growth rate of rice,the ratio of biomass distribution to leaf,N concentration of shoot,the amount of net light interception and the number of adventitious roots.4.(1)When rice population was built,the N level are both N270 when LAI reaches to the highest under HD and LD.At maximum-tillering,booting,and heading stage,the corresponding N level for leaf chlorophyll content reach the greatest value is N270,N180,N270,respectively,meanwhile,the ratio of chlorophyll a and b increased with the duration of the growth stage.(2)In a certain range,leaf photosynthetic rate increases with the N level increasing,and has a significant positive correlation with grain yield.Influence degree of N level on different sites leaf photosynthetic rate was Top 1>Top 2>Top 3;From heading to maturity,the decline proportion of photosynthetic rate of all leaves was all about 60%,and the degradation rate of Rubisco enzyme was all about 75%.(3)At different growth stage or some time of one day,the canopy temperature all decrease with N level increasing,and had a significant negative correlation with grain yield;At night the difference among different N level became smaller,;There are negative correlation between canopy temperature and leaf water content,transpiration rate,row humidity,carbon and nitrogen ratio.Besides,there were no significant difference between HD and LD for all indexes.5.(1)When N concentration in different sites leaf,shoot and sheath of rice reached to maximum,the corresponding N level increased with leaf site,shoot site and sheath site rise.During grain yield formation process,the mean value of reduction ratio for N concentration is leaf(70.4%)>sheath(48%)>shoot(21.8%);for non-structural concentration(NSC)concentration is sheath(41.4%)>shoot(25.1%)>leaf(-23.5%).(2)The changes of N and NSC concentration in different sites leaf,shoot and sheath are different:for N,the reduction concentration ratio are all about 70%in different sites leaf and are all about 48%in different sites sheath,but in different sites shoot is top 1>top 2,and no significant change in top 3 and rest shoot;For NSC,the NSC concentration in different sites leaf,shoot,and sheath all reduce during the early filling stage,while there are significant increasing during the late filling stage;Moreover,the change ratio of their N and NSC concentration are all trend to stable when N level is N180.(3)During filling process,grain N concentration increase with N level increase;At heading stage,grain NSC concentration decrease with N level increase,subsequently,there is no difference for NSC concentration among all N levels.Moreover,there is no difference for all indexes between HD and LD.6.(1)Panicle length,panicle branch number and kernels number per panicle are all affected by N level and transplant density;due to grain weight and setting percentage are also affected by N level,there is no significant difference for their per panicle weight at maturity;Meanwhile,the filling process characteristics of superior and inferior grain are significantly affected by N level:when N level is less than N180,grain filling rate is obviously greater than that under higher N level.(2)Grain N concentration increase with N level increasing,and basically stable during filling process,and grain N concentration in superior grain is 6.7%higher than in inferior grain at maturity;Grain P concentration decrease with N level increasing,meanwhile,the concentration increased during filling process,and grain P concentration in superior grain is 9.5%higher than in inferior grain;At early grain filling stage,grain K concentration increase with N level increasing,and decrease obviously during filling process,meanwhile,the difference of grain K concentration among nitrogen levels is reducing.And grain K concentration in superior was 46.7%lower than in inferior grain.(3)Leaf pruning more,per panicle weight decreased more,mainly affected by the reducing of setting percentage and inferior grain yield.Under the same pruning way,the influence degree increased with N level increasing.Besides,there is no difference for grain filling characteristics under HD and LD. |
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