The Effects Of Nitrogen Application Timing On Dry Matter Accumulation Of Soybean

A pot experiment was conducted to study the effects of N application timing on dry matter accumulation of soybean with basal N, topdressing N and starter-N plus topdressing N under same N level (N50kg/ha). The dry matter accumulation in soybean leaves, stems, petioles, pods was determined. The main results are as follows.The starter-N+top dressing N (N15+35R4) treatment improved the dry matter accumulation in soybean organs after R4. The dry matter accumulation increased with the increase of basal fertilizer before R4in various soybean organs. The dry matter accumulation related with application of nitrogen, absorption ability of root and nodule nitrogen fixation ability after R4. The rate of accumulation of dry matter on starter-N was the highest. At harvest, the order was as follows: N15+35R4>N15+35R3>N0+50R4>N0+50R3>N50, N15+35R4and N15+35R3were higher than N50by24.5%and21.9%(P<0.01). Starter-N plus topdressing N could delay the period of leaf maximum area, slow down leaf senescence. N15+35R4, had the biggest leaf dry matter accumulation, provided sufficient space for photosynthetic products for the later part, Topdressing N also increased leaf productivity of soybean at later stage. Compared with N50, the leaf productivity for N15+35R3and N15+35R4increased by165.4%and128.3%(P<0.01). Topdressing N increased N content in leaves, delaying leaf senescence, increasing the photosynthetic capacity of soybean at later stage.These shows that starter-N (N15kg/ha) promoted root growth and nodule formation. No fertilizer-N or too much fertilizer-N will hinder root nodule growth; affect absorption capacity of nutrients, not conducive to the dry matter accumulation in later stage of soybean.Topdressing N reduced dry matter translocation at R4, and improved assimilation capacity after R4. The dry matter translocation at stem, leaf and petiole for basal fertilizer was greater than topdressing N treatments. Compared with N0+50R3, N0+50R4, N15+35R3and N15+35R4, the N50dry matter translocation increased by14.6%,23.6%,44.8%and34.1%(p<0.05). Compared with N50, the N0+50R3, N0+50R4, N15+35R3and N15+35R4material assimilation after R4increased by14.4%,28.7%,62.5%and67.4%, differenees between N15+35R4, N15+35R3and N50was significant at1%level. The material assimilation increases was much faster than the reduction in the quantity of substance transportation speed in topdressing N treatments. Topdressing N retarded the period of the maximum net assimilation rate, which was in favor of photosynthetic products in filling period of soybean. The effect of N15+35R4was most remarkable.Compared with N50, the N15+35R4increased yield by30.4%(P<0.01). Compared with N0+50R3, N0+50R4and N15+35R3, the N15+35R4yield increased by27.1%(P<0.01), 18.6%(P<0.05) and4.3%. Topdressing N at R4was better than at R3.