| It is of theoretical and practical importance to clarify the effect of planting density and nitrogen fertilization rate on the growth and development, carbon-nitrogen metabolism, and grain yield in the establishment of cultivation technologies for super highly-yielding winter wheat. In the study, a field experiment was carried out at Gaocheng County, Hebei Province, during 2013-2014 growing season, using a winter wheat cultivar, Shimai 18. The experiment was designed as split plot arrangement, with planting density as main plots(150×104, 225×104, 300×104 and 375×104 plants·hm-2, expressed in D150, D225, D300 and D375, respectively) and nitrogen fertilization rate as split plots(N 180, 240 and 300 kg·hm-2, expressed in N180, N240 and N300, respectively). The main results were summarized as follows:The amounts of population culms(spikes) of wheat increased with the increase of planting density during all growing stages, but the difference of culms(spikes) among the four densities became smaller with the growth process, so that all the four densities got enough spikes at maturity. The total spiking percentage and spiking percentage from tillers decreased, and the spiking percentage from main stems increased with the increase of planting density, and the percentage of spikes from tillers were more than that from main stems in all the four densities. The leaf area index(LAI) and dry matter accumulation during pre-winter to anthesis increased with the increasing density, but the LAI and dry matter accumulation in D150 and D225 were higher than those in D300 and D375 during post-anthesis period. The harvest index, however, decreased with the increase of planting density. The LAI and dry matter accumulation had a tendency to increase with the increasing nitrogen fertilization rate. The harvest index, however, decreased with the increasing nitrogen rate. The LAI of wheat with different fertilization rates were not significantly different before booting stage, but the LAI with higher nitrogen fertilization rates declined slower after anthesis.The net photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO2 concentration(Ci), transpiration rate(Tr) and chrolophyll SPAD of flag leaves increased since anthesis, and reached a peak at 12 days after anthesis, then decreasing. The photosynthetic parameters mentioned above and chrolophyll SPAD of flag leaves at all determination dates decreased with the increase of planting density. The senescence of flag leaves were delayed in lower density teratments, so that the photosynthetic efficiency was improved during late period. Pn, Gs, Ci, Tr and chrolophyll SPAD of flag leaves at all determination dates increased with the increase of nitrogen fertilization rates from N180 to N240, and decreased when the nitrogen fertilization rate increased to N300 i.e., with that of N240 the highest, but the difference between N240 and N300 was not significant.The nitrogen accumulation amounts in leaf blade and stem/leaf sheath of wheat during early-middle growing period increased with the increase of planting density, but the difference of nitrogen accumulation amounts among the four densities became smaller with the growth process. And the nitrogen accumulation amounts in leaf blade and stem/leaf sheath in lower densities D150 and D225 were higher than those in higher densities D300 and D375 at anthesisstage. The amount of nitrogen accumulation in grain, and the amount and rate of nitrogen transportation from leaf blade and stem/leaf sheath decreased with the increase of planting density. Nitrogen accumulation amount in vegetative organs usually increased with the increase of nitrogen fertilization rate. The nitrogen accumulation amount in grain, and the nitrogen transportation amount and rate from leaf blade and stem/leaf sheath increased with the increase of nitrogen fertilization rate under the densities D150 and D225. Under the densities D300 and D375, however, the nitrogen accumulation amount in grain, and the nitrogen transportation amount and rate from leaf blade and stem/leaf sheath decreased with the increasing nitrogen rate. The nitrogen transportation rate from stem/leaf sheath, spike axis/glumes decreased with the increase of nitrogen fertilization rate, but the nitrogen trantsportation rate from leaf blade increased with the increase of nitrogen rates from N180 to N240, and decreased when the nitrogen fertilization rate increased to N300, with the highest trantsportation rate from leaf blade appeared in the nitrogen fertilization rate N240.The concentrations of total soluble sugar and total N in leaf blade, stem/leaf sheath and grain during pre-winter to anthesis decreased with the increase of planting density. Under the fertilization rate N180, the highest total N concentration in grain was in the density D300. Under the fertilization rates N240 and N300, however, the highest total N concentration in grain was in D225. The C/N in leaf blades of the lower densities D150 and D225 were usually higher than those in the higher densities D300 and D375 during jointing to anthesis. The C/N in stem/leaf sheath, spike axis/glumes, grain and the whole plant usually decreased with the increase of density. of wheat with lower densities D150 and D225 during the whole growing period increased with the increase of nitrogen rate, but in those with higher densities D300 and D375, only the concentration of total soluble sugar in the vegetative organs during early growing period increased with the increase of nitrogen fertilization rate. And after jointing stage, the concentration of total soluble sugar in leaf blade, stem/leaf sheath decreased with the increase of nitrogen fertilization rate. Under the densities D150 and D225, the highest total N concentration in grain was achieved in the fertilization rate N240. Under the densities D300 and D375, however, N180 had the highest Total N concentration in grain. The among the three nitrogen rates had no significant variation under the same density, but the C/N ratios in grain decreased with the increase of nitrogen fertilization rate.The effect of planting density on yield and the three yield components of wheat was statistically significant(P<0.05). The effect of nitrogen fertilization rate on 1000 grain weight and grain yield was also significant(P<0.05). The interactions of planting density and nitrogen rate on grain weight and grain yield were significant. With the increase of planting density, the amounts of spikes per hectare increased, but the difference of spike amounts among the four densities was not significant statistically. In contrast, the grains per spike and 1000 grain weight decreased with the increase of density. The spike amount in D150 was significantly higher than that in D375, and the 1000 grain weights in D150 and D225 were significantly higher than those in D300 and D375. Grain yield decreased with the increase of density. And the difference of yield among the four densities became more significantly with the increasing nitrogen fertilization rate. Under the same density, the amounts of spikes per hectare and grains per spike increased with the increase of nitrogen fertilization rate, but the 1000 grain weight did not have a significant trend. Under lower densities, higher grain yields was achieved in the the treatments with more nitrogen fertilized, but under higher densities, the treatments with less nitrogen fertilized got higher yields.Correlation between C/N and yield showed that, higher C/N in leaf blade and stem/leaf sheath during jointing to anthesis was beneficial to improve grain yield, and higher C/N in whole plants during booting to anthesis was beneficial to improve grain yield.All the results showed that, the highest grain yields of wheat, 10308.65 and 10221.98 kg·hm-2, were achieved in the treatments with the planting density 150×104·hm-2, and the nitrogen fertilization rates 240 and 300 kg·hm-2. In the treatments, the size of LAI were appropriate during whole growing period, and the LAI declined slowly during late growing period. The chlorophyll SPAD of flag leaves were higher and maintain a longer time compared with those of other treatments, so that the photosynthetic performance of wheat was improved, and favorable to the accumlation of photosynthetic products. And in the two treatments, the concentrations of total soluble sugar and total N in wheat grains were significantly increased, and the nitrogen transportation from vegetative organs to grains was also promoted, so as to keep the metabolic activity of grains. Higher C/N ratios in the plants of wheat were maintained during booting to anthesis in the two treatments, meaning suitable carbohydrates supply to grain filling and increasing grain weight. Suitable spikes per hectare and more grains per spike were also achieved in the two treatments, and so that, the hightest yields were achieved. According to the results of the study, it is recommended that, nitrogen fertilization be increased properly under low planting density. Considering saving cost and improving nitrogen use efficiency, nitrogen input be decreased under high planting density, so as to realize high yield and high efficiency of wheat production. |
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