Regulation Effect And Mechanism Of Combined Root And Leaf Nitrogen Supply On Nitrogen Use Efficiency Of Winter Wheat

The experiment was conducted in the experimental field of xuanzhuang Village（116°54’E,36°12’N）,Daolang Town,Tai’an City,Shandong Province during 2019-2020 and2020-2021 wheat growing season.Jimai 229 was used as material,and two nitrogen levels were set,240 kg hm^-2（traditional n rate,N1 reduced by 20%on the basis of traditional N rate,N1）and 144 kg hm^-2（40%on the basis of traditional N rate,N2）,respectively.The two nitrogen spraying times were 7 d after anthesis（T1）and 21 d after anthesis（T2）,respectively.And four urea concentration levels of 0%,2%,6%and 10%were represented by R0,R2,R6and R10 respectively.In ¹⁵N micro-zone labeling test,N（common urea）was applied at jointing stage+¹⁵N（labeled urea）was applied at flowering stage,and N（AN）was not sprayed on leaves after flowering,and N（A7）was sprayed on leaves 7 days after flowering,N（A14）was sprayed on leaves 14 days after flowering,and N（A21）was sprayed on leaves 21 days after flowering.¹⁵N（labeled urea）was applied to the root at jointing stage+N（ordinary urea）was applied to the root at flowering stage,and N was not sprayed as JN on the leaves after flowering,but AS J7 on the leaves after flowering,A14 on the leaves after flowering,and J21on the leaves after flowering.Set N（common urea）at jointing stage+N（common urea）at flowering stage,and ¹⁵N is LN without spraying on the leaves after flowering,¹⁵N is L7 on the leaves after flowering,¹⁵N is L14 on the leaves after flowering,and 1¹⁵N is L21 on the leaves after flowering.The main results are as follows:1.Effects of different combinations of nitrogen spraying on SPAD value and enzyme activities related to nitrogen metabolism of winter wheatUnder the same nitrogen spraying combination（nitrogen spraying period and nitrogen spraying concentration）,the SPAD values of flag leaves after flowering were R2>R0,R6,R10,and the GS and NR activities were R2>R6,R10>R0.The SPAD value,GS activity and NR activity of flag leaves were significantly increased by nitrogen spraying after anther,and the increase was the largest when urea concentration was 2%.When the concentration of urea solution was 2%,delaying the spraying time from 7 d after anther to 21 d after anther could delay the decline of SPAD value and NR activity of flag leaves.2.Effects of different combinations of nitrogen spraying on nitrogen uptake,transport and distribution in winter wheatUnder the same combination of nitrogen injection,the nitrogen accumulation of organs in N1 treatment was significantly higher than that in N2 treatment,and increasing the amount of nitrogen application in root could improve the nitrogen accumulation of organs in winter wheat at maturity.Under the same conditions of root nitrogen application rate and leaf nitrogen spraying period,the total nitrogen accumulation of winter wheat aboveground organs was R2,R6,R10>R0,indicating that spraying urea solution on leaf after flowering could improve the nitrogen accumulation of winter wheat aboveground plants and promote the absorption of nitrogen by winter wheat plants.Compared with spraying water after flowering,flower nitrogen injection can significantly improve the winter wheat flowering after assimilation of nitrogen input kernels,while nitrogen injection time of flowering after assimilation of nitrogen input kernels had no significant effect,but improve the spraying urea concentration can significantly increase the assimilation of nitrogen input kernels after flowering,and n application rate of 240 kg hm^-2 in the root showed a higher growth.The translocation of storage nitrogen from vegetative organs to grains and the nitrogen harvest index before anthesis increased first and then decreased with the increase of urea concentration,and reached the highest at 2%concentration.Too high concentration of urea spraying was not conducive to the translocation of nitrogen to grains before anthesis.When 2%urea solution was applied on leaves and the spraying time was delayed from 7 d after anthesis to 21 d after anthesis,the translocation of storage nitrogen from vegetative organs to grains increased significantly before anthesis.3.Effects of different nitrogen injection combinations on winter wheat yield and protein contentNitrogen spraying after anthesis could increase 1000-grain weight and grain yield of winter wheat,and the increase was the largest when urea spraying at 2%concentration level was applied,and the effect of nitrogen spraying after anthesis on grain yield was more obvious when nitrogen reduction was 40%(144 kg hm^-2).Under the same nitrogen application rate,the grain yield of T2 treatment was significantly higher than that of T1 treatment,but this phenomenon was only observed when spraying urea solution with 2%concentration,indicating that only under the condition of spraying urea solution with appropriate concentration（2%）,delaying the time of nitrogen application could further improve the grain yield.Nitrogen spraying after anthesis can increase protein content and protein yield of winter wheat grain,and the increase rate is larger by using 2%urea solution.In addition,under the condition of lower nitrogen application rate in root,the improvement effect of nitrogen spraying after anthesis on grain nitrogen content and protein content was decreased,and the improvement effect on grain protein yield was enhanced.4.Effects of different combinations of nitrogen spraying on nitrogen use efficiency of winter wheatWith the decrease of nitrogen application rate,nitrogen use efficiency and partial nitrogen productivity increased.Nitrogen use efficiency and nitrogen use efficiency of winter wheat were significantly improved by nitrogen spraying after anthesis,and the increase rate was greater when nitrogen was reduced by 40%(144 kg hm^-2)compared with conventional nitrogen application rate(240 kg hm^-2).With the increase of spraying urea concentration,nitrogen use efficiency,nitrogen use efficiency and nitrogen partial productivity increased firstly and then decreased,and reached the highest at 2%concentration.When 2%urea solution was applied on the leaf surface and the spraying time after anther was delayed,the increase of nitrogen use efficiency,nitrogen use efficiency and partial nitrogen productivity of winter wheat was greater.5.Effects of nitrogen injection at different stages after anthesis on accumulation,distribution and transport of nitrogen from different sources in winter wheatPost-anthesis nitrogen spraying could significantly promote the uptake of nitrogen by winter wheat roots,and delaying post-anthesis nitrogen spraying could significantly reduce the transport of absorbed nitrogen from nutrient organs to grains.Post-anthesis nitrogen spraying could not only promote the translocation of temporary storage nitrogen from pre-anthesis organs to grains,but also promote the translocation of post-anthesis assimilated nitrogen from roots and leaves to grains.Post-anthesis nitrogen spraying could significantly reduce the accumulation and distribution of nitrogen from foliar nitrogen spraying in grains,improve its accumulation and distribution in vegetative organs,and also improve the translocation and distribution of nitrogen from root topdressing to grains,thus significantly increasing the accumulation of nitrogen from root topdressing in grains.6.Effects of nitrogen injection at different stages after anthesis on yield and nitrogen use efficiency of winter wheatPost-anthesis n injection had no significant effect on spike number of winter wheat,but only increased grain yield by increasing 1000-grain weight,and the increase of 1000-grain weight and grain yield increased with post-anthesis N injection delay.Nitrogen spraying after anthesis could improve the nitrogen use efficiency of winter wheat,and the time of spraying after anthesis had a significant effect on the nitrogen use efficiency.The postponement of post-anthesis nitrogen spraying to 21 days after flowering was more beneficial to the improvement of nitrogen use efficiency of winter wheat compared with 7 and 14 days after flowering.In conclusion,spraying 2%urea solution on the leaves of winter wheat after flowering can increase the SPAD value of flag leaves and the activities of enzymes related to nitrogen metabolism,and promote the absorption and assimilation of nitrogen in roots and the redistribution of temporary storage nitrogen to grains of winter wheat after flowering,thus significantly improving grain yield and nitrogen use efficiency.In addition,delaying the post-flowering nitrogen spraying period reduced the distribution of nitrogen from leaf surface to grain,promoted its distribution to leaf and glume,delayed the senescence of photosynthetic organs,prolonged the filling time,and also improved the transport and distribution of nitrogen from root to grain from vegetative organs,and improved the nitrogen use efficiency.Thus,nitrogen accumulation,1000-grain weight,grain yield and nitrogen use efficiency could be synergistically improved at mature stage.