| The sustainable development of agriculture not only needs to increase crop yield,but also needs to reduce the application of chemical fertilizer,improve the efficiency of nutrient utilization and reduce the pollution of chemical fertilizer application to the environment.The selection and popularization of nitrogen(N)efficient maize cultivars is the most simple and effective way to increase maize yield,reduce N fertilizer application and increase N use efficiency.The study used nitrogen efficient(N-efficient)maize cultivar ZH 311 and nitrogen inefficient(N-inefficient)maize cultivar XY 508 as experimental materials,through the combination of field pot experiment,field experiment and hydroponic culture experiment,and set different N levels and N management were conducted in 2014-2016.To investigate the higher yield and N efficient mechanism of N-efficient cultivar ZH 311,evaluated the effects of N application on yield formation,N absorption and utilization of maize cultivars with different N efficiency,the dry matter production,N accumulation and translocation,and root morphology,physiology and N absorption characteristics of maize,as well as the N balance in maize production system.The main results are as follows:1.Compared with the N-inefficient cultivar XY 508,N-efficient cultivar ZH 311 could effectively increased the aveage lateral root length to increase total root length,total root surface area and total root volume under low N stress.Those changes led to the Vmax FW-1 and Vmax plant-1 of N-efficient cultivar ZH 311 were significantly higher than those of N-inefficient cultivar XY 508,while the Km value obviously lower than that of XY 508,suggesting that the root N uptake ability of N-efficient cultivar ZH 311 were significantly higher than that of N-inefficient cultivar XY 508.Higher root N uptake ability of ZH 311 obviously increased the maximum accumulation rate,average accumulation rate,and root N uptake rate,and ultimately made the N accumulation of N-efficient cultivar ZH 311 significantly higher than that of N-inefficient cultivar XY 508.Therefore,we can concluded that higher root N uptake ability is an important physiological mechanism of ZH 311 to efficiently acquire N,especially under N deficient conditions.The higher N uptake ability of the N-efficient cultivar ZH 311 than that of the N-inefficient cultivar XY 508 was mainly the result of lower Km value and higher N uptake rate,especially during the later growth period.2.Higher maximum accumulation rate and average accumulation rate,later maximum accumulation rate time point,and longer rapid accumulation period contributed to the N accumulation of N-efficient cultivar ZH 311 were significantly higher than that of N-ineffficient cultivar XY 508,indicating that the N-efficient cultivar ZH 311 had higher N accumulation ability compared with N-ineffficient cultivar XY 508.There were significant influences of N fertilizer rate and N management on N accumulation of maize.The advantages of N-efficient cultivar ZH 311 over N-ineffficient cultivar XY 508 in N accumulation were more obvious at low N levels with rational base to topdressing ratio(50:50),while the superiority decreased and gradually lost under high N levels and high topdressing ratio(25:75).Rational base to topdressing ratio(50:50)was beneficial to increase the N accumulation of ZH 311,while increase topdressing ratio(25:75)was more conducive to improve the N accumulation of XY 508.3.Pre-silking N translocation and translocation efficiency of N-efficient cultivar ZH 311 were obviously higher than those of N-inefficient cultivar XY 508 led to the N uptake efficiency,N recovery efficiency,N agronomic efficiency,and N partial factor productivity of ZH 311 significantly higher than those of XY 508,while the apparent N losess and losess efficiency markedly lower than those of XY 508.There were significant influences of N fertilizer rate and N management on the differences between ZH 311 and XY 508 on N absorption and utilization,and apparent N losess.The differences between ZH 311 and XY 508 on N absorption and utilization,and apparent N losess were initially increased and then decreased with the increase in N levels and topdressing proportion.The greatest differences on N absorption and utilization,and apparent N losess were at low N levels and 50%base fertilizer + 50%topdressing.Therefore,compared with the N-inefficient cultivar XY 508,the advantages of N-efficient cultivar ZH 311 in improving N absorption and utilization and reducing apparent N losses is more obvious under low N levels.With 50%base fertilizer + 50%topdressing could more effectively play the advantages of N-efficient cultivar ZH 311,while 25%base fertilizer + 75%topdressing significantly reduced the apparent N losses.4.Low-N stress significantly affected the chlorophyll content,the photosynthetic and chlorophyll fluorescence parameters.The degrees of variation of these indices in N-efficient cultivar ZH 311 were obviously lower than those in N-inefficient cultivar XY 508,and the variation between two cultivars were increased with prolong of treated times.Maize seedlings could increase Chl a/Chl b,apparent quantum yield,and light saturation point to adapt to low nitrogen stress.Compared with N-inefficient cultivar XY 508,N-efficient cultivar ZH 311 maintained higher Pn and electron transport rate for stronger PS ? activity,which further promoted a stronger ability to harvest and transfer light.This could be a photosynthetic mechanism that the N-efficient cultivar used to efficient absorption and utilization nitrogen.5.Compared to N-inefficient cultivar XY 508,delayed maximum increasing rates point onset,increased maximum increasing rates,average increasing rates,and final theoretical biomass yield,and prolonged duration of rapid growth period effectively increased the dry matter accumulation and crop growth rate of N-efficient cultivar ZH 311 in different growth periods,especially in the later growth stage.Greater proportion of vegetative organs,and uniform aerial-and underground dry matter distribution contributed to higher dry matter production ability in the later growth stages,and lower pre-silking dry matter translocation and translocation efficiency delayed the senescence of photosynthetic organs led to the biomass yield significantly higher than that of XY 508.6.The application of N fertilizers significantly increased the grain yield by increasing the number of grains per panicle and 1000-kernel weight.The mean number of grains per panicle and the mean grain yield of N-efficient cultivar ZH 311 were significantly higher than those of N-inefficient cultivar XY 508,while the 1000-kernel weight of XY 508 were obviously higher than that of ZH 311,those indicated that the N-efficient cultivar had a significant advantage on grain yield over the N-inefficient cultivar mainly due to its higher number of grains per panicle.The advantage that ZH 311 had over XY 508 in terms of grain yield was significantly influenced by the N fertilizer rate and N management.The advantages that ZH 311 over XY 508 in terms of grain yield were initially increased and then decreased with the increase in N levels and topdressing proportion.The greatest grain yield advantages N-efficient cultivar ZH 311 over N-inefficient cultivar XY 508 were 0.93 t hm-2and 1.48 t hm-2at 247.5 kg N ha-1 and 61.35%base fertilizer + 38.65%topdressing,respectively.Moreover,the grain yield both of ZH 311 and XY 508 were initially increased and then decreased with the increase in N levels in 2015,suggesting that excessive application of N fertilizer could not only resulted in increasing grain yield,but also reduced grain yield,and the optimal N fertilizer rate of N-efficient cultivar ZH 311 was obviously lower than that of N-inefficient cultivar XY 508. |
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