| In order to study the effects of starter-N plus topdressing N on dry matter accumulation, number of pods in different canopies and yield of soybean under different densities, a field experiment was conducted with soybean cultivar Dongnong52, using a split-plot design with three densities (200000,250000, and300000plants-ha-1and three N application patterns (a single application of N60kg·ha-1as basal fertilizer; N18kg·ha-1as basal fertilizer followed by topdressing N42kg·ha-1at stage R3; N18kg·ha-1as basal fertilizer followed by topdressing N42kg·ha-1at stage R4). Main results are shown as following:Under the same density, comparing with using N only as basal fertilizer, starter-N plus topdressing N produced more dry matter of plants, leaves, petioles and pods in upper/middle canopies after stage R5; topdressing N at stage R4was better than at stage R3. There was no significant differences between different stems treatments in the upper/middle canopies. At stage R7, comparing with using N only as basal fertilizer under250,000plants·ha-1, leaf dry matter for topdressing N at stage R4in upper canopy was increased by12.0%(P<0.05) and the statistics for middle canopy was99.3%(P<0.01); petiole dry matter for topdressing N at stage R4in upper canopy was increased by13.5%(P<0.05) and the statistics for middle canopy was8.4%(P<0.05); pod dry matter for topdressing N at stage R4in upper canopy was increased by4.8%, the statistics for middle canopy was13.1%(P<0.05). Experimental results indicated that topdressing N can meet the needs of plant at seed-filling stages, which in hence increased different organs dry matter in upper/middle canopies.Within the same N application pattern, dry matter of different organs/m2in middle canopy increased with increment of density before stage R6. At stage R7, dry matter of different organs/m2in upper/middle canopies under the density of250,000plants·ha-1was significantly higher than the statistics for300,000plants·ha-1. Dry matter of different organs per plant declined with increment of density. At stage R8, comparing with using N only as basal fertilizer under200,000plants·ha-1pod dry matter per plant in upper canopy for topdressing N at stage R4under250,000plants·ha-1was increased by3.2%, and the statistic for pod/m2was29.0%(P<0.05). In middle canopy, the the dry matter of pod per plant was increased by11.7%(P<0.05) while the statistic for pod/m2was39.7%(P<0.01). Experimental results indicated that topdressing N in the late development stage can make up the disadvantages brought by high density and increase the dry matter of different organs/m2in upper/middle canopies under the density of250,000plants·ha-1 At maturity, the percentage of≤2-seed pods was higher than other pods in upper/middle canopies. Under the same density, starter-N plus topdressing N increased the number of pods in upper/middle canopies. The number of3/4-seed pods in upper/middle canopies for starter-N plus topdressing N at stage R4was higher than other treatments. The number of≤2-seed pods in upper/middle canopies for starter-N plus topdressing N at stage R3was higher than other treatments. Within the same N application pattern, the number of≤2-seed pods in upper/middle canopy reached a maximum under the density of300,000plants·ha-1, while the best density for3/4-seed pods was250,000plants·ha-1. There was no significant differences between different treatments in the bottom canopy.The yield increased when the density increased from200,000plants·ha-1to250,000plants·ha-1, but the yield declined when the density increased to300,000plants·ha-1. The increasing density resulted in the decrease of seed number of per plant, while topdressing N at late development stage optimized individual plants in higher densities. Seed number of per plant for starter-N plus topdressing N at stage R4under250,000plants·ha-1was7.0%(P<0.05) more than number for using N only as basal fertilizer under200,000plants·ha-1and the number of seeds/m2was increased by33.8%(P<.005). Yield was increased by36.%(P<0.05)... |
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