| Wheat and maize cropping system was widely used in recent years to achieve one ton ofgrain yield. This study was conducted in field trial in winter wheat and summer maize cropingsystem to investigate how to improve utilization efficiency of nitrogen fertilizer in thiscropping system. Seven nitrogen fertilizer application rate, including0kg·hm-2(N0),56.25kg·hm-2(N1),112.5kg·hm-2(N2),168.75kg·hm-2(N3),225kg·hm-2(N4),281.25kg·hm-2(N5),337.5kg·hm-2(N6), and two nitrogen topdressing stage including jointingstage (S1) and jointing and anthesisstage (S2) were selected, applying with15N isotope tracertechnique, to explore the effects of nitrogen management in winter wheat season on nitrogenaccumulation, distribution and translocation, and regulation effect on grain formation fromthe perspective of physiology and ecology, aiming to provide a theoretical basis and technicalsupport for the formulation of reasonable nitrogen management.1Effects of nitrogen management in wheat season on nitrogen accumulation anddistribution of winter wheat and summer maizeNitrogen accumulation of winter wheat atanthesis, of grain at maturity and of vegetativeorgans continually increased with elevating nitrogen application rate. While treatment N5andN6showed no significant difference, indicating the elevated nitrogen amount in treatment N6,compared to treatment N5, did not improve nitrogen accumulation of winter wheat. Nitrogenaccumulation of summer maize grain at maturity showed the trend: N6, N5,N4>N3>N2>N1, indicating adding25%~50%of nitrogen on the basis of N4in wheat seasondid not significantly influent the nitrogen accumulation of summer maize grain at maturity.Compared with topdressing at jointing stage, topdressing at jointing andanthesis improvednitrogen accumulation of winter wheat atanthesis, nitrogen accumulation of grain at maturityin treatment N3and N4condition, and nitrogen accumulation of summer maize grain,indicating S2treatment improved the nitrogen accumulation in winter wheat and summermaize cropping system, compared to S1treatment. 2Effects of nitrogen management in wheat season on nitrogen uptake from differentsources in winter wheat and summer maizeWith increasing nitrogen application, increment of nitrogen accumulation from soil indifferent wheat organs inanthesis showed the trend leaf>stem+leaf sheath>husk+ear axis,indicating the elevated nitrogen application was more distributed to leaf. Nitrogenaccumulation from fertilizer and distribution proportion of wheat at maturity showed the trendN5, N6>N4, N3, and nitrogen accumulation from soil showed the contrary order, indicatingadding25%of nitrogen on the basis of N4treatment improve the nitrogen accumulation fromfertilizer at wheat maturity, but no influence with adding50%of nitrogen on the basis of N4treatment. Under the same nitrogen application rate, translocation of nitrogen derived fromfertilizer and soil in leaf and stem+leaf sheath was higher than that in husk+ear axis, withthe highest translocation proportion in leaf, followed by stem+leaf sheath, the lowest in husk+ear axis. Translocation of nitrogen derived from soil in leaf, stem+leaf sheath and husk+ear axis was higher than that derived from fertilizer in N3, N4, N5treatment; however, N6showed the contrary order, indicating adding50%of nitrogen on the basis of N4treatmentinhibited the translocation of nitrogen derived from soil in vegetative organs to grain, notfavorable for the improvement of nitrogen harvest index.With increasing nitrogen application in wheat season, nitrogen of summer maize plantatanthesis, which derived from fertilizer applied in wheat season, enhanced significantly andthe proportion of nitrogen derived from fertilizer applied in wheat season accounted for3.81%~16.59%. Nitrogen of summer maize grain, which derived from fertilizer applied inwheat season showed the trend N6, N5>N4>N3and N6>N5>N4>N3in leaf+stem sheathand husk+ear axis, indicating adding25%~50%of nitrogen on the basis of N4applicationrate in wheat season did not significantly influent the accumulation of nitrogen derived fromfertilizer applied in wheat season in summer maize grain but adding50%of nitrogenimproved the nitrogen accumulation in vegetative organs.Nitrogen utilization efficiency in wheat season showed the trend N3, N4, N5>N6and N5,N6>N4>N3, and N4, N5>N3>N6in terms of utilization efficiency of residual nitrogen andnitrogen utilization efficiency of the whole year, respectively, indicating adding or subtracting25%of nitrogen on the basis of N4in wheat season did not significantly influent nitrogenutilization efficiency of wheat plant but adding25%of nitrogen improved utilizationefficiency of residual nitrogen and adding more25%of nitrogen significantly decreasednitrogen utilization efficiency in wheat season and of the whole year. 3Effects of nitrogen management in wheat season on nitrogen loss in winter wheat andsummer maize cropping systemThe ammonia volatilization rate reached the highest in the second day after the basalapplication and topdressing of nitrogen, and then declined. However, a new peak wouldappear due to rainfall and the peak level related to the volume of rainfall. Under the samenitrogen application condition, the highest ammonia volatilization rate and accumulation inS1was higher than those in S2after topdressing in high level nitrogen application treatments.With increasing nitrogen application rate in wheat season, ammonia volatilization rate andaccumulation after basal application of nitrogen in summer maize season continually rose andthe differences of ammonia volatilization rate and accumulation between treatmentsdiminished continually after topdressing at male tetrad stage. Topdressing at jointing andanthesis stage in wheat season enhanced ammonia volatilization rate after basal application insummer maize season but did not significantly influent the ammonia volatilization rate andaccumulation after topdressing at male tetrad stage.With increasing nitrogen application in wheat season, nitrate nitrogen content in deep soilsignificantly increased at maturity in wheat and maize season, resulting in nitrogen lossthrough leaching. Compared to topdressing at jointing stage, topdressing at jointing andanthesis stage increased nitrate nitrogen content in0~40cm soil layer at maturity in wheatseason, and decreased nitrate content in60~140cm soil layer at maturity in summer maizeseason.4Effects of nitrogen management in wheat season on carbon metabolism in winterwheat and summer maizeUnder the condition of topdressing at jointing stage, adding25%of nitrogen on the basis ofN4significantly increased dry matter accumulation of grain at maturity in wheat and maize,improving the increment of grain dry matter accumulation after flowering in winter wheat butno significant effect by adding more nitrogen application. Under the condition of topdressingat jointing and anthesis stage, adding25%of nitrogen on the basis of N4did not significantlyinfluent the grain dry matter accumulation in winter wheat and summer maize andtranslocation of dry matter in vegetative in wheat.Under the same nitrogen application rate, compared to topdressing ate jointing stage inwheat season, topdressing ate jointing and anthesis stage enhanced dry matter accumulationof grain after flowering and its contribution proportion, and improved dry matteraccumulation of grain and vegetative organs at maturity in summer maize. 5Effects of nitrogen management in wheat season on yield of winter wheat and summermaizeUnder the condition of topdressing at jointing stage, reducing nitrogen application on thebasis of N4treatment decreased the biomass and yield of winter wheat and summer maize.Adding25%of nitrogen improved biomass of winter wheat and summer maize but did notsignificantly influent the yield. However, adding50%of nitrogen did not significantlyinfluent the biomass and yield, indicating the addition of nitrogen on the basis of N5wasinvalid input. Adding25%~50%of nitrogen on the basis of N2did not significantly promotethe biomass of winter wheat and summer maize when topdressing at jointing and anthesisstage.Under the same nitrogen application rate, topdressing at jointing and anthesis stage did notsignificantly improve the biomass of winter wheat but significantly enhanced wheat yield inN3and N4treatment and promote the improvement of biomass and yield of summer maizecompared to topdressing at jointing stage.6Effects of nitrogen management in wheat season on nitrogen utilization efficiency ofwinter wheat and summer maizeUnder the same topdressing stage, with the increasing nitrogen application in wheat season,nitrogen agronomic efficiency and nitrogen partial factor productivity in wheat significantlydecreased but those in maize continually improved. Nitrogen use efficiency of the whole yearrose firstly and then decreased continually, with the highest value in N4treatment. Comparedto topdressing at jointing stage, topdressing at jointing and anthesis stage in wheat seasonimproved nitrogen agronomic efficiency and nitrogen partial productivity of winter wheat andsummer maize and improved the utilization of residual nitrogen from wheat season in summermaize.It was concluded that nitrogen application rate at225kg·hm-2with topdressing at jointingand anthesis stage might be the optimal nitrogen management in wheat season under winterwheat and summer maize cropping system and the experimental condition, by integrating theresults in terms of grain yield, nitrogen agronomic efficiency, nitrogen partial productivity,and nitrogen use efficiency.
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