Effects Of N Fertilization At Different Stages On Nitrogenase Activity And Yield Of Soybean

Pot experiments were carried out at Northeast Agricultural University in 2005 and 2006, thevarieties used were Heinong 37 and Longxuan 1. N fertilizer was applied at different stages on thesame level in 2005 and three levels in 2006. Dry weight of root and root nodule, nitrogenaseactivity, dry weight and nutrient content of plant were measured, and the effect of N fertilization atdifferent stages on nitrogenase activity, dry matter accumulation, nutrient accumulation and yield ofsoybean, were analyzed.The treatments were N25×3,N30+45 (R₃), N30+45 (R₄), N75 and CK. in 2005. The resultsshowed that during the stages VE-R₃, N75 restrained the growth of root and root nodule becausethe basal N was excessive. N25×3 and N30+45 decreased the restraining effect on root throughdecreasing the basal N. Root nodule and root dry weight were higher than NO and the restrainingeffect of N on nitrogenase activity was obvious at R₃, N0＞N30+45 (R₄)＞N25×3＞N30+45 (R₃)＞N75. From R₄ to R₆, the inhibition of N on root was reduced, root and root nodule dry weight ofeach treatment increased obviously, and reached peak values at R₅. Topdressing increased the rootaccumulation amount at this stage obviously, and the best topdressing stage was early pod fillingstage. The result of dry weight at R6 indicated that topdressing can delay the disintegration of rootefficiently at the later stages. N25×3, N30+45 (R₃) and N30+45 (R₄) treatments shifted the peakvalue of nitrogenase activity to R₅, and the N75's occurred at R₄. The nitrogenase activity of eachtreatmentwas in the order of N30+45 (R₄)＞N30+45 (R₃)＞N25×3＞N75＞NO at R₆. Correlationanalysis shows that the nodule nitrogenase activity had a negative correlation with theaccumulation of nitrogen in early stage, and nitrogenase activity at R₅ stage had a significantlypositive correlation with yield.The result of dry matter and nutrient accumulation showed that N25×3, N30+45 (R₃), N30+45(R₄) gained more N and dry matter accumulation, the effect of N30+45 (R₄) was the best, N anddry matter accumulation were 5.501g/pot and 199.38g/pot, respectively. The accumulation ofvarious growth stages indicated that topdressing could delay the degeneration or root system andpromote dry matter and nutrients accumulation in pod filling stage. The yield data showed thatN30+45 (R₄)＞N30+45 (R₃)＞N75＞N25×3＞N0. The yields of N30+45 (R₄)and N30+45 (R₃)increased 8.85% and 5.35% than N75, respectively. The results of yield factors showed that theyield increase was mainly because of promoting the pod and seed number per plant, topdressing at R₅ had good effect on 100-seed weight. Yield have positive correlation with nutrient and dry matteraccumulation at pod filling stage and negative correlation with dry matter accumulation at VE.Base on the experiment in 2005, we designed three N levels N25, N50 and N75 in 2006, andapplied nitrogen at different stages on N50 and N75. Comparison of N75 with N50 indicated thatexcessive N can not promote yield, and the treatment of N25×3 promoted the utilization rate of Nthrough adjusting the fertilization stages. The result of dry matter and nutrient accumulationshowed that N25×3＞N75 at N75 level, and N25×2 (R₄)＞N25×2 (R₃)＞N25×2 (R₁) at N50 level.The results of yield was in the order of N25×2 (R₄)＞N25×3＞N25×2 (R₃)＞N25×2 (R₁)＞N50＞N75＞N25. Compared with N50, the yield of 25×2 (R₄), N25×2 (R₃) and N25×2 (R₁)increased 23.1%, 8.35% and 1.22%, 25×2 (R₄) respectively significant at 5%. Compared with N75,the yield of 25×3 increased 18.17%, significant at 5%.The results of two-year experiments showed that suitable N application in accordance withbasal fertilization, decreasing the basal N application have positive effect on promoting root growthin early period and increasing nutrient and dry matter accumulation amount in later period.