| In order to clarify the effect of different planting densities and nitrogen applicationrates on summer maize’s growth and development, carbon-nitrogen metabolism, grainyield, and to provide reasonable technology for high-yielding and super high-yieldingsummer maize in Hebei Province, a field experiment by split plot design was carried out inGaocheng County, Hebei Province with planting densities (including52500,60000,67500,75000and82500plants/ha) as main plots, and nitrogen application rates (including300,375and450kg/ha) as split plots. A summer maize cultivar, Nongdan902, was used asexperimental materials. The agronomic traits and physiological index, such as, kernelyields and yield components, LAI, stem traits, dry matter accumulation and transportation,soluble sugar and nitrogen concentrations in leaf blades, sheaths and stems,carbon-nitrogen ratio and so on, was determined under different planting densities andnitrogen application rates. The main results were summarized as follows:1. With the increase of planting density, the fertile ears per hectare increased, but thekernels number per ear and1000-kernel weight significantly decreased under all level ofnitrogen application rates. But the kernel yield of maize increased with the increase ofplanting density and reached the maximum yield at the planting density67500plants/ha,and decreased at further higher planting densities. The main yield-related trais, such as earlength, ear diameter, kernel rows per ear, and kernels per row, all decreased, but the lengthof sterile tip of ears increased, with the increase of planting density. The fertile ears perhectare, kernels per ear,1000kernels weight and kernel yield of maize under the nitrogenapplication rate375kg/ha were all significantly higher than those under the nitrogenapplication rates300and450kg/ha. The fertile ears per hectare and1000kernels weightwere not significantly different between the nitrogen application rates350and450kg/ha,but the kernels per ear and kernel yield under the nitrogen application rate450kg/ha weresignificantly higher than those under N300kg/ha. The main yield-related characters, suchas ear length, ear diameter, kernel rows per ear, and kernels per row improved, and thesterile tip of ears shortened, with the increase of nitrogen application rate from N300to375kg/ha, but all the traits became poorer with the increase of nitrogen application ratefrom N375to450kg/ha. In all treatments, the highest kernel yield12797.3kg/ha was achieved at the planting density67500plant/ha and nitrogen application rate375kg/ha.2. The leaf area indexes (LAI) and stem characters were different under differenttreatments of planting density and nitrogen application rates. The LAI was reachedmaximum at silking stage for all treatments. With the increase of planting density, the LAIat early and middle stages significantly increased. While increasing the planting density to75000and82500plants/ha, the leaves senesced earlier and the LAI decreased moresharply than those in lower planting densities. The LAI at various growing stages increasedwith the increase of nitrogen application rates from300to375kg/ha, and decreased whenthe nitrogen rate increased to450kg/ha. The optimum amount of nitrogen application rate,N375kg/ha, improved the LAI and delayed leaf senescence. As the planting densityintensified, the index of stem diameter decreased, the index of ear height increased, and thestem lodging resistance decreased. While a reasonable increase of nitrogen applicationcould improve the stem lodging resistance.3. The Dry matter accumulation per plant decreased, while the dry matteraccumulation per hectare increased with the increasing planting density. With theincreasing planting density to75000and82500plants/ha, the increase of dry matteraccumulation per hectare were not statistically significant compared to that under thedensity67500plants/ha. With the increase of nitrogen rate, dry matter accumulation perplant and per hectare firstly increased, and then decreased. The optimum nitrogenapplication rate (375kg/ha) could not only improved dry matter production, but alsobenefited the amount of dry matter production after silking and the amount of dry mattertranslocation.4. The effect of planting density and nitrogen application rate on carbon-nitrogenmetabolism was significant. The content of total soluble sugar and nitrogen, andcarbon-nitrogen ratio in leaf blades, sheathes and stems all decreased with increasingplanting density. The content of total N in leaf blades, sheathes and stems all increasedwith nitrogen application rate intensified. But the performance of the content of totalsoluble sugar was different, which increased with the application rate increasing from300to375kg/ha, the decreased with the increasing N from375to450kg/ha. Thecarbon-nitrogen ratio of leaf blades and stems/sheathes were also different. During maletetrad stage to30days after silking, the carbon-nitrogen ratio in leaf blades increased withthe increasing N from300to375kg/ha, but decreased with the N increasing from375to450kg/ha. The carbon-nitrogen ratio of stems/sheathes, however, decreased withincreasing nitrogen application rate.5. The relation between carbon-nitrogen ratio and yield showed that, the grain yieldper maize plant was positively related to the carbon-nitrogen ratio of leaf blades andstems/sheathes among different level of planting densities. Among different level ofnitrogen rates, the carbon-nitrogen ratio of leaf blades, as the organ of photosynthesis, was higher under the nitrogen rate375kg/ha, meaning a status of reasonable carbon-nitrogenmetabolism benefited the development of grain yield. While the stem, as the transportationorgan of photosynthetic products, reached a comparatively lower carbon-nitrogen ratiounder the nitrogen rate375kg/ha, that means a coordinating source-sink relationship toimprove the grain yield.6. The amount of nitrogen accumulation in grains and plants were all the highest withthe nitrogen application rate375kg/ha under all planting densities. But the nitrogenharvest index, nitrogen use efficiency and nitrogen uptake efficiency were all the highestunder the lower nitrogen application rate,300kg/ha.All the results showed that, the optimum treatment was planting density67500plant/ha and nitrogen application rate375kg/ha for the cultivar Nongdan902. Under thetreatment of planting density and nitrogen application rate, the coordinated carbon andnitrogen metabolism was highlighted by rational development of leaf area, higher drymatter and nitrogen accumulation, higher harvest index and higher ability of dry matterproduction during later growing period, comparatively higher yield of per plant, andoptimum combination of yield components. The optimum planting density and nitrogenapplication rate provide a good production technique for highly yielding summer maize. |
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