Effects Of Nitrogen Topdressing At Different Spring Leaf Stage On Yield Formation And Grain Quality Of Winter Wheat

In wheat production,nitrogen topdressing is one of the most important measures to regulate the process of growth and development,and therefore,to realize the purposes of high yield,good quality,lodging resistance and yield stability.In order to clarify the effects of nitrogen topdressing at different spring leaf stage on the growth and development of high yield wheat population and individual plants,yield formation process and grain quality,and to provide theoretical basis and technical support for high yield and high quality cultivation of winter wheat,a field experiment was conducted in the teaching and experimental farm of Hebei Agricultural University at Xinji County,Hebei Province,during 2016-2017 winter wheat growing season.The field experiment was arranged with split plot design,with three commercial strong gluten winter wheat cultivars,GY2018,KN2009 and SH4366 in main plots,and nitrogen topdressing at the time when spring leaves 3,4,5 and 6 sprouted respectively?expressed in N3,N4,N5 and N6,respectively?as split plots,on the basis of total N240 kg·hm^-2,with 50%as basal dressing,the other 50%of nitrogen was as topdressing.The main results were as follows:1.With the nitrogen topdressing treatment in spring,the amount of population culms?spikes?,LAI and dry matter accumulation of winter wheat began to differ significantly at jointing stage.The responses of the three cultivars to nitrogen topdressing stage were consistent.The population culm amount,LAI and dry matter accumulation of the treatments N3 or N4,which were nitrogen topdressed earlier,were the largest at jointing stage.And those of N4 were the largest since booting stage until maturity.These results showed that nitrogen topdressing at the 4th spring leaf stage is beneficial to the increase of population parameters of winter wheat.2.The flag leaf chlorophyll SPAD of N6 of all cultivars were the highest from 0to 7 days after anthesis,and then decreased rapidly,so that the difference among treatments were insignificant from 14 to 28 days after anthesis.But the chlorophyll SPAD of N4 was the highest at 28 days after anthesis,while that of N5 or N6 the lowest.The post-anthesis P_n of flag leaves for all cultivars increased with delaying nitrogen topdressing.Comprehensively,topdressing nitrogen at the 4th of 5th spring leaf stage is beneficial to keep higher photosynthetic ability of flag leaves during grain filling period.3.The difference of spikes per hectare among treatments with nitrogen topdressing at different spring leaf stage was statistically significant,with that of N4the most,but insignificantly differing from that of N5 in all the three cultivars.The difference of grains per spike was generally insignificant among nitrogen treatments,with the only exception for the cultivar SH4366,in which the grains per spike of N4was significantly less than those of N3 and N6.The difference of 1000 grain weight among different nitrogen treatments showed similar tendencies,with that of N4 the highest for all cultivars.The grain yields of N5 in GY2018,and of N4 in KN2009 and SH4366,were the highest in all nitrogen treatments,but the difference between N4and N5 was insignificant for all cultivars.During the period since anthesis stage until24 days after anthesis,the grain filling rates of N4 and N5 were higher for all the three cultivars.Considering the comprehensive effect on yield characters,the stage from spring leaves 4 to 5 was the favorable nitrogen topdressing stage.4.At jointing stage,the plant height of N3 and N4 were significantly taller than those of N5 and N6,while that of N4 was the tallest,and that of N6 the shortest from booting to maturity stage of all cultivars.The gravity center height of N3 and N4 were taller than those of N5 and N6 for all the three wheat cultivars.The leaf stage of spring nitrogen topdressing had only small influence on the diameter,wall thickness,fillingness,mechanical strength and lodging resistance index of the 1st internode,but had greater influence on those of the 2nd internode,especially on the 30th day after anthesis,when the difference of all the above parameters were significant among nitrogen topdressing treatments for all the three cultivars,with the fillingness,wall thickness and mechanical strength of the two basal internodes of N5 and N6treatments significantly higher than those of N3 and N4 for all cultivars.The lodging resistance indexes generally increased with delaying nitrogen topdressing.Correlation analysis showed that,the mechanical strength and lodging resistance indexes of the basal 1th and 2nd internodes were negatively correlated to the gravity center height,and positively correlated to the diameter,wall thickness and fillingness of the basal 1st and 2nd internodes,both very significantly.These results showed that,the lodging resistance is closely related to the quality of basal 1th and 2nd internodes of wheat stem.The good quality of basal internodes of wheat stem is a key link to increase the lodging resistance of wheat plants.5.The nitrogen accumulation amount in leaves and spikes,and of the whole wheat plants at anthesis,and that in all organs and whole plants at maturity of the three cultivars of N4 were the highest while those of N6 the lowest.At anthesis,the distribution percentage of nitrogen in stem and leaf sheath of N5 or N6 treatment was the highest,while that of N3 or N4 the lowest in all cultivars.However,the distribution percentage of nitrogen in leaves of N3 or N4 was the highest,while that of N5 or N6 the lowest.At maturity,the accumulation amount and distribution percentage of nitrogen in grains were the highest in all organs.Comparing among the four nitrogen topdressing treatments,the accumulation amount in grains of N4 were the highest.The nitrogen uptake efficiency of N4 of all cultivars was the highest,and that of N6 the lowest.The nitrogen fertilizer production efficiency was significantly different among nitrogen topdressing treatments in GY2018 and KN2009,with N5 and N4 the highest,while N3 and N6 the lowest,respectively.Nitrogen utilization efficiency increased with delaying nitrogen topdressing for all cultivars.6.The grain protein content and wet gluten content of N4 were the highest in all cultivars,but the difference among nitrogen topdressing treatments was not significant.The grain protein yields of GY2018 and KN2009 were significantly different among nitrogen topdressing treatments,with N4 the highest while N3 or N6 the lowest.The regulation effect of nitrogen topdressing at different spring leaf stage on the flour quality parameters differed significantly in different wheat cultivars.The longest dough developing time in the cultivar GY2018 was achieved in the treatment N6,but in N4 for KN2009,and in N5 for SH4366,respectively.The longest dough stable time and largest farinograph quality number for GY2018 were achieved in N4 treatment,while in N3 for KN2009,and in N5 for SH4366,respectively.But the weakening degree of the corresponding treatment was the smallest.The gluten index declined with the delaying nitrogen topdressing for all the three cultivars.As topdressing at spring leaf 4 stage?N4?was best for yield formation and grain quality,but the lodging resistance was poor.And topdressing at spring 5 stage?N5?was beneficial to lodging resistance with a relatively higher yield and better quality insignificantly different to those of N4.As a result,nitrogen topdressing at spring leaf5 was the best stageto realize the multiple targets of high yield,stable yield and good quality of winter wheat.But in winter wheat production area of Hebei plain where spring irrigation water often becomes a limiting factor,it is all suitable to topdress nitrogen at spring leaf 4 to 5 stage accompanying the irrigation,which is decided according to irrigation conditions.