Nitrogen Use Efficient Of Summer Maize And Agronomic And Physiological Characteristics Of Nitrogen-efficient Hybrids

The determination of nitrogen application rate and high-yield maize hybrids selection are effective ways to improve maize yield and efficiency of nitrogen.Breeding and applying maize hybrids with both high yield and high efficiency of nitrogen is extremely important for maize production.Exploring the response characteristics of maize to nitrogen and the physiological and ecological mechanism of maize hybrids with high efficiency of nitrogen are the basis for developing maize nutritional physiological breeding and nutrient management.This study was conducted in the Guanzhong Irrigation District,and five local main summer maize hybrids were selected to determine the effects of nitrogen fertilizer and maize hybrids on grain yield,nitrogen use efficiency,soil nitrate nitrogen and dry matter（nitrogen）accumulation and translocation in four years continuous field experiment.Response to nitrogen fertilizer,evaluate and screen different types of nitrogen-efficient varieties:double high-efficiency hybrids（high yield and high efficiency of nitrogen under both high and low N conditions（Zhengda12））;low-nitrogen tolerant varieties:high yield under low-nitrogen conditions（Shandan609）),study the radiation and water use efficiency of different nitrogen-efficiency hybrids and diagnosis of nitrogen nutrition in different plant organs,and systematically analyze the leaf source and root traits,grain filling characteristics and non-structural carbohydrate differences of low-nitrogen tolerant hybrids,clarifying the agronomic characteristics and nutritional and photosynthetic physiological characteristics of high nitrogen-efficient maize hybrids.The main research results are as follows:1 Summer maize hybrids differences in maize grain yield and use efficiency of nitrogen under different nitrogen application ratesThe results of the four-year experiment showed that nitrogen application increased maize yield by 14-38%.The overall performance of grain yield and nitrogen use efficiency of hybrids was that there was not significantly different among Zhengda 12,Xianyu 335 and Zhengdan 958,and they are significantly greater than Qiangsheng 101,Shandan 609 being the smallest.Zhengdan 958 and Qiangsheng 101 maintained the same yield under N225(application nitrogen rate 225 kg ha^-1)and N300(application nitrogen rate 300 kg ha^-1),and under N0（no nitrogen application）and N150(application nitrogen rate 150 kg ha^-1)treatments,grain yield of Zhengdan 958 was significantly higher than Qiangsheng 101.According to the performance of yield and efficiency of nitrogen,we define Zhengda 12 as a double high-efficiency hybrid,Shaandan 609 as a double-low-efficiency hybrid;according to the yield performance under low nitrogen and high nitrogen,Zhengdan 958 was defined as a low-nitrogen tolerant hybrid,Qiangsheng 101 was defined as a non-low-nitrogen tolerant hybrid.The residual nitrogen content in soil varied from 157 to 300 kg ha^-1 under N225treatment during the growing season of summer maize,and accumulated more severely under excessive nitrogen application up to 349 kg N ha^-1.According to the response curve of yield,apparent nitrogen loss,and nitrogen use efficiency to nitrogen application rate,it is recommended that the soil nitrogen supply before sowing for high-yield and high-efficiency summer maize in this area（the cumulative amount of nitrate nitrogen in the soil layer 2 m before sowing+the amount of nitrogen applied）was 280～350 kg N ha^-1.The selection of double high-efficiency varieties and low-nitrogen-tolerant varieties can increase yield by11%-16%.Compared with the general nitrogen application rate of 300 kg N ha^-1 in the local area,the nitrogen application rate can be reduced by 25%-34.3%.The selection of high N-efficient hybrids can ensure low nitrogen losses,and can reduce the risk of nitrate leaching.Therefore,the selection of high N-efficient hybrids and the reasonable selection of nitrogen application rate can achieve a win-win situation for both grain yield and environment.2 Responses dry matter（nitrogen）accumulation and translocation of summer maize hybrids to nitrogen application ratesThe difference in yield between nitrogen fertilizers and hybrids is determined by the grain weight and grain number per spike and the effect of grain number per spike is greater than the difference caused by grain weight.In the Guanzhong irrigation area,dry matter accumulation increased by 16.3%-30%.The contribution of biomass to the change of grain yield is 71%on average.The contribution rate of dry matter accumulation to grain yield of summer maize hybrids after anthesis ranges from 84.8 to 93.7%,and the dry matter remobilization rate of vegetative organs ranges from 5%to 13.1%.For summer maize hybrids,the contribution rate of nitrogen accumulation after anthesis to grain nitrogen accumulation ranges from 37.3 to 57.9,and the remobilization efficiency of vegetative organ nitrogen is between 44.5%and 54.7%.The contribution of vegetative organ nitrogen remobilization to grain nitrogen ranges from 47.5%to 57.8%,and the nitrogen remobilization rate showed a downward trend with the increase of nitrogen application rate.With the increase of nitrogen application rate,its remobilization and contribution to grain nitrogen showed a downward trend.There was a significant positive correlation between the genotypic difference in grain nitrogen concentration and the difference in nitrogen remobilization in vegetative organs.The contribution rate of grain nitrogen concentration to grain nitrogen accumulation can reach 50%.The characteristics of Xianyu 335 show that the nitrogen concentration of the hybrid can be guaranteed while maintaining high yield,which is due to its high NHI,which is related to its high stem nitrogen remobilization efficiency.Selecting varieties under low nitrogen conditions can use nitrogen uptake efficiency as a screening index,and under high nitrogen conditions,nitrogen physiological use efficiency can be used as a screening index.3 Studies on radition,nitrogen and water use efficiency of maize hybrids with different efficiency of nitrogenTwo hybrids,Zhengda 12 and Shandan 609 with significant differences in grain yield and nitrogen use efficiency under low and high nitrogen conditions,were used as experimental materials to study the resource use.The selection of nitrogen-efficient varieties with high specific leaf nitrogen content（SLN）can achieve efficient utilization of water,radition and nitrogen resources.Under the same SLN,nitrogen-efficient varieties show higher resource utilization efficiency.The quadratic relationship between SLN and WUE,RUE,NUE and yield can be used to determine the best combination.SLN is between1.5～1.8g N cm^-2.In the meantime,resource utilization efficiency and yield will no longer increase,and resources can be utilized to the greatest extent,thereby maximizing grain yield.4 Diagnosis of nitrogen nutrition in different parts of maize varieties with different efficiency of nitrogenThe critical nitrogen concentration dilution curves established for the two maize hybrids based on leaves（LDM）,stems（SDM）and plants（PDM）dry matter,and the equation of"Zhengda 12"are:N_c=2.64 LDM^-0.204、N_c=1.58 SDM^-0.388、N_c=2.33 PDM^-0.263;The equation of"Shaandan 609"is:N_c=2.61 LDM^-0.205、N_c=1.83 SDM^-0.337、N_c=2.47PDM^-0.237.There is no significant difference in the critical nitrogen concentration dilution curve established based on leaves between the two maize hybrids.The difference in plant nutrition is mainly caused by the nitrogen nutrition status of the stem.Compared with the double-low-efficiency hybrid,the double-efficiency variety has a low stem nitrogen concentration per dry matter.（a value）,high stem nitrogen concentration dilution rate（b value）.In order to save costs,the critical nitrogen concentration dilution curves established based on leaves（LDM）and stems（SDM）dry matter can be used to replace the critical nitrogen concentration dilution curves established based on plants（PDM）dry matter;when the three critical nitrogen concentration dilution curves were compared for yield prediction,it was found that the relationship between relative yield（RY）and NNI,cumulative nitrogen deficit（AND）at different growth stages was highly significant with R² being the largest in V12 and VT stages,confirming the stability of the relationship in both V12 and VT periods and gave a good indication of the variation of RY under limiting and non-limiting nitrogen and allowed estimation of summer maize yield.The results of this study provide ideas for nitrogen fertilization management of pre-flowering maize to improve yield.In this study,there was a significant positive correlation between NNI and phase yield,and a significant negative correlation between NNI and agronomic nitrogen use efficiency and nitrogen recovery efficiency.5 Source（leaf and root）characteristics of low-nitrogen tolerant maize hybrids under different nitrogen application ratesTwo hybrids,Qiangsheng 101 and Zhengdan 958 with different tolerance to low nitrogen,were used as experimental materials to compare the source difference（leaf and root）.The results showed that Zhengdan 958,which was tolerant to low nitrogen,had higher yield and absorbed more nitrogen under lower nitrogen application rates(0 and 150 kg N ha^-1),and showed higher nitrogen use efficiency.There were no significant differences in grain yield and nitrogen use efficiency between N225 and N300 treatments.Under low nitrogen conditions,compared with Qiangsheng 101,Zhengdan 958 can ensure a higher leaf nitrogen concentration and specific leaf weight,slow down the effect of low nitrogen on the photosynthetic system of the plant,and maintain a higher PSⅡeffective light quantum efficiency（Fv/Fm）,photochemical quenching coefficient（q P）and PSⅡactual photon yield（ΦPSⅡ）,so as to ensure that more light energy is used in the process of photosynthetic electron transfer,and provide a structural and material basis for ensuring a higher net photosynthetic rate（Pn）.At the same time,it has high photosynthetic nitrogen utilization rate,so as to achieve high radition and nitrogen use efficiency.Deeper root distribution,longer root length and larger root effective absorption area ensure high nitrogen accumulation.These characteristics.The combination of these characteristics ensures that low-nitrogen-tolerant hybrids have higher above-ground and underground biomass,and ultimately achieves higher material production capacity under low-nitrogen conditions.6 Grain filling and non-structural carbohydrates characters of low-nitrogen tolerant maize hybridsLow-nitrogen tolerant hybrids had higher rates of grain filling,earlier initiation of filling of the apical kernels,and no significant differences in the basal kernels under low nitrogen application rates.Under low nitrogen conditions,low-nitrogen tolerant hybrids maintained relatively high grain carbohydrate utilization capacity,especially in the apical kernels.In addition,lower leaf starch and stem sucrose in the low-nitrogen tolerant varieties also favored grain filling under low-nitrogen conditions.In summary,this study concluded that grain yield and radiation,nitrogen and water use efficiency can be effectively improved by selecting and breeding high nitrogen-efficient hybrids,which can also reduce soil nitrate nitrogen residues and leaching.Breeding of low-nitrogen tolerant hybrids is an effective way to improve nitrogen efficiency.Excellent leaf photosynthetic characteristics,high photosynthetic nitrogen efficiency,deeper root distribution,longer root system,higher effective root absorption area and higher grain carbohydrate use capacity can be used as reference indicators for the selection and breeding of high N-efficient hybrids.