The Limiting Factors Of Maize Productivity And The Corresponding Regulation Mechanism In The North China Plain

The North China Plain(NCP)is one of the most important agriculture production areas and maize is one of the most cereal crops.It is earthshaking to ensure the maize yied in the NCP for food security in China.To definite the limiting factors to spring and summer maize,the present study analysised the differences about growth and development and meteorological factors of spring and summer maize,which were the main maize planting pattern in the NCP.Also,the mechanism that affected the kernel number and kermel weight and the technology that release the limiting factoes were researched in this study.The main results as follows:The relation analysis between kernel number per plant(KNP)and meteorological factors at key stage(15d per-silking to 15d post-silking)was conducted by a 6-year field experiment data.The excessive precipitation and low solar radiation would reduce the KNP,however,the heat stress had on effects on the KNP.The drought or overcast and rainy stress during the critical period would decrease the KNP of spring maize and the main limting factor to the KNP of summer maize was the rainfall and low radiation in the key period.In addition,the filling rate in the early stage of filling in spring maize was lower compared with summer maize.The main reason was that the maximum temperature in the stage was 1.68oC higher than summer maize.However,the filling rate of summer maize declined fast in the late stage due to the temperature and solar radiation declined.To demonstrate the optimal stage for supplemental irrigation with limiting wate and improve the drought resistance for spring mazie,the irrigation was supplemented at V6,V12,VT and 15d after silking,respectively.The irrigation at late stage(IVT?IS15)consumed more water after silking compared with the early irrigation treatments.And the early irrigation could stimulate maize vegetative growth,which accumulated more nitrogen compared to the late irrigation treatments.In addition,the more nitrogen was reserved in the soil compared with the early irrigation tretments,which could be utilized by maize in the filling stage.Most importantly,the irrigation at tasseling would ensure maize growth and promote kernel growth,and maintain leaf function after silking.The relation between source and sink was optimized.The regression analysis of grain yield and water/nitrogen consumption percentage pre-silking and post-siling also demonstrated more water(20-50%)and nitrogen(40-60%)were consumed,and higher grain yield could be achieved.To explore the mechanism that the overcast and rainy stress decreased kernel number and the corresponding remission technology,we shaded the maize for 6 days with 70%black polypropylene fabricat at V14 and VT,respectively,and detassel ing was conducted simultaneously to regulate canbanhyrate transportation.The shade treatment significantly reduced tho photosynthetic rate and decreased the soluble sugars concentration in the stem.And the anthosis-silking interval(ASI)was dramatically lengthened.As a consequence,the KNP observably reduced by the shade stress.Fortunately,the remoal of tassel could elininate the apical dominance in maize,which motivated assimilations portioning to ear,especially under shading condition.The soluble sugars concentration in the ear section of stem was dramatically improved.As a consequence,the ASI was shortened and KNP was observably increasesd by detasseling.From the jointing stage to the tasseling stage,normal concentration and double concentration ED AH(27%ethephon and3%DA-6)were sprayed at each leaf auricle appeared,respectively,which could shape different architectures.The treatnents during V9-V15 would significantly reduce the paint height,the treatments during V6-Vllwould distinctly inhibit leaf growth and the ED AH,especially the high concentration ED AH was sprayed durng V7-V13 obviously decreased grain yield Most importantly,the ED AH that sprayed at V14 and V15 would significantly reduce the intemode length above ear,however,the treatments at this period did not inhibit leaf growth,and highest grain yield was attained.Further,we analyzed the“source-sink-translocation,system in the plant of EDAH-treated at V14.The results indicated that the ED AH did not change the photosynthetic rate,i.e.,the source was not inhibited by the EDAHL The sink activity of kernel also stayed approximate level as the CK,and the kermel accumulated more starch compared with the CK.The main variation was the intemod length above ear was dramatically bridged.The EDAH visibly increased the soluble sugars concentration in the stem,especially the in ear section.In addition,the carbon isotopic tracer also demonstrated that shorting the internode length above ear could improve assimilation transportation of upper leaves,which could remarkably increase kermel number per ear in maize.The EDAH was foliar applied at the jointing stage to enhance summer mai2e lodging resistance,and 6-benzyladenine(BA)and brassinolide(BR)were separately sprayed at tasseling to regulate kermel endosperm cell division.The results showed that the two hormones sprayed at tasseling could hamper leaf senescence,improve photosynthesis and significantly increase the number of kernel endosperm,resulting in a high grain filling rate and high kernel weight.As a result,the tasseling treatments increased grain yield by 2.9-16.0%in both years.We concluded that the lag stage played a vital role in constructing sink capacity,and treating maize with BA or BR at tasseling can apparently increase the source and sink capacity to improve the grain filling rate and yield,i.e.,ensuring optimized growth condition at this period was extremely important for high yield production in maize.