Effects Of Nitrogen Rates On Wheat Yield And Quality Under Different Soil Fertility Conditions

In order to investigate the effect of nitrogen fertilizer on grain yield and quality of winter wheat under different fertility conditions,the cultivars ‘Fengdecun 5’ with strong gluten wheat and ‘Bainong 207’ with medium gluten were used as experimental materials.Four nitrogen（N）application rates,including 0 kg·hm^-2、120 kg·hm^-2、240 kg·hm^-2 and 300 kg·hm^-2,were applied in four sites to study the effects of different nitrogen application rates on grain yield and quality of winter wheat under different fertility conditions.The main results are as follows:1.Effects of nitrogen application on physiological characteristics and yield formation of wheat at filling stage under different soil fertility conditionsHigh SPAD value is beneficial to maintain higher photosynthetic capacity.With grain filling,the SPAD value of flag leaf decreased.Nitrogen application significantly increased the SPAD value of flag leaf after anthesis,which kept a high level at the later stage of grain filling,and prolonged the photosynthetic duration of leaves.Soil fertility,nitrogen fertilizer and their interaction had significant effects on wheat yield,spike number,grain number per spike and 1000-grain weight.Increased nitrogen application significantly increased the number of wheat spikes and grains per spike.The yield improvement under nitrogen application was mainly due to the increase of spike number and grain number per spike.The performance of wheat fields with different fertility was different: under low fertility conditions,nitrogen fertilization had the greatest effect on increasing the number of grains per spike;under medium fertility conditions,nitrogen fertilization had the most obvious effect on the regulation of spike number;under high fertility conditions,the regulation effect of nitrogen application on grain yield and its factors is relatively small.Grain yield and its factors also showed differences between cultivars in different years.In 2019-2020,there were significant differences between cultivars in wheat yield,grain number per spike,and 1000-grain weight.The three factors of wheat yield in 2020-2021 were significantly different between varieties,but there was no significant difference in grain yield.2.The effect of nitrogen application on the content of wheat protein components under different soil fertility conditionsWith grain filling,total protein content first decreased and then increased,and there were differences between cultivars.Albumin and globulin showed a decreasing trend,while prolamin and glutenin showed an increasing trend.Nitrogen application significantly increased the grain protein content in the whole growth stage,and the regulation of gliadin and glutenin content was greater than that of albumin and globulin.Soil fertility,nitrogen application rate and their interaction had significant or extremely significant effects on wheat grain protein components,and the regulatory effect of nitrogen application rate was greater than that of soil fertility.With the increase of nitrogen application rate,the content of components of grain protein increased significantly,and the largest increase was prolamin;the regulation effect of nitrogen fertilizer on the content of protein components was most significant under low fertility conditions.Improving soil fertility also increased grain albumin,globulin,and prolamin content,while gluten content was higher at low fertility condition.Under different fertility conditions,the nitrogen application rate of 240 kg·hm^-2 maintained a higher protein content,and with the increase of nitrogen fertilizer,the protein content decreased or did not change significantly.3.Effects of nitrogen application on the content of starch components in wheat under different soil fertility conditionsSoil fertility had a very significant effect on the total starch and amylopectin content of grains,nitrogen application had a very significant effect on amylose,and cultivar had a significant effect on amylose content,amylopectin content and amylose/branch ratio.The effect of nitrogen fertilization on starch content varied among soil fertility: Nitrogen fertilizer at high fertility condition had no significant effect on starch content of grains,but nitrogen application at low fertility condition significantly reduced the content of total starch and components,and the decrease of strong gluten cultivar was greater than that of medium gluten cultivar.The content of total starch and starch components in grains treated by ‘Fengdecun 5’ with nitrogen application rate of 240 kg·hm^-2 and ‘Bainong 207’ with 300 kg·hm^-2 was the lowest.4.Effects of nitrogen application on main processing quality of wheat under different soil fertility conditionsNitrogen fertilization can improve wheat sedimentation value,increase wet gluten content,and prolong dough formation time and stability time.The effect of nitrogen fertilizer regulation was different among different sites.The regulation effect of nitrogen application on sedimentation value and wet gluten content was more significant under low fertility conditions.The comprehensive analysis showed that the sedimentation value and wet gluten content of the two cultivars at the high fertility condition were best treated with nitrogen application rate of 180 kg·hm^-2,while the improvement effect was the best in the nitrogen application range of 240-300 kg·hm^-2 under the condition of low and medium fertility soil.Under different fertility conditions,increasing nitrogen fertilizer application significantly prolonged the formation time and stabilization time of the two cultivars.Compared with the two cultivars,the formation time and stabilization time of ‘Fengdecun 5’ were significantly higher than those of ‘Bainong 207’,indicating that genotype was the main factor determining the dough formation time and stabilization time.Under the condition of no nitrogen fertilizer,the dough formation time of ‘Fengdecun 5’ was the largest at the high fertility condition,but the increase of the dough formation time of nitrogen application at each experimental site was as follows: medium fertility condition>low fertility condition >high fertility condition.5.The relationship between wheat yield and quality indexsCorrelation analysis showed that there was a significant or extremely significant positive correlation between the contents of total grain protein,prolamin,glutenin and GMP and the main processing quality indexs,indicating that the grain protein content,especially the storage protein content,had a positive effect on the flour processing quality.The sedimentation value and wet gluten content were significantly positively correlated with the dough forming time,but not significantly correlated with the stabilization time.Starch peak viscosity was significantly negatively correlated with total starch and amylose content.Using principal component analysis,17 quality indicators were transformed into 3 independent comprehensive indicators: gluten and dough quality,starch quality and gelatinization quality,reflecting 74.6% of the original quality information.At the low and medium fertility sites,two cultivars had better dough quality and starch quality within the nitrogen application range of 240-300 kg·hm^-2;At high fertility sites,the effect of nitrogen fertilizer on quality is relatively small,but the variation between two cultivars is large.Under the same nitrogen application conditions,the protein and dough quality of ‘ Fengdecun 5’ were significantly higher than those of‘Bainong 207’.The correlation between wheat yield and quality indicators showed that grain yield was significantly positively correlated with the main quality indicators under medium and low-fertility conditions,while yield was only significantly correlated with protein content in high-fertility conditions.Under the conditions of medium and low fertility,the yield and quality of wheat could be improved synergistically when the nitrogen application rate was 240 kg·hm^-2;in the high-fertility wheat field,the effect of nitrogen fertilizer on the yield and quality was relatively small,and the nitrogen application rate was 180 kg·hm^-2 can achieve better comprehensive wheat yield and quality.