| Shaanxi Guanzhong Plain is one of the main producing areas of summer maize in China.It is of great significance to realize the high efficiency,high quality and high yield of maize in this area to ensure China’s grain production.Nitrogen application is an important measure to improve maize productivity in this area.However,long-term single and excessive application of nitrogen fertilizer not only failed to significantly increase crop yield,but also caused excessive growth of crop groups,poor stem quality,reduced mechanical strength,resulting in lodging risk,resulting in reduced yield and quality,and a series of ecological and environmental problems.Therefore,in view of the problems of unreasonable application of nitrogen fertilizer and low utilization efficiency in maize production in Guanzhong area,this study conducted a two-season（2020-2021）summer maize field experiment with’Shaandan609’as the test variety in Caoxinzhuang Experimental Farm of Northwest A&F University.A two-factor experimental design was adopted to set three nitrogen application rates:low nitrogen application rate(L:135 kg N·ha-1),medium nitrogen application rate(M:180 kg N·ha-1)and high nitrogen application rate(H:225 kg N·ha-1).Two kinds of nitrogen fertilizer types:conventional urea（NU）and controlled release urea and conventional urea1:1（CRUNU）,by studying the effect of nitrogen application rate and nitrogen fertilizer type on the growth,lodging resistance and yield of summer maize and its mechanism,to provide reasonable nitrogen fertilizer application scheme and theoretical basis for high yield,high efficiency and sustainable production of maize in Guanzhong area.The main results are as follows:1.In the two growing seasons of summer maize,compared with high nitrogen application rate,plant height decreased by 2.4%and 5.5%,ear height decreased by 5.5%and 12.7%,barycenter height decreased by 4.5%and 8.3%under medium and low nitrogen application rates,respectively.There was no significant difference in plant height,ear height and barycenter height between medium and low nitrogen application rates.Dry matter accumulation and its distribution in various organs increased with the increase of nitrogen application rate,but there was no significant difference in dry matter accumulation and its distribution in various organs between medium nitrogen application rate and high nitrogen application rate in CRUNU treatment.Compared with NU treatment,CRUNU treatment reduced plant height,ear height and center of gravity height by 1.5%-3.2%,3.7%-6.2%and3.2%-40%,respectively.At the same time,CRUNU treatment could effectively promote dry matter accumulation and distribution in various organs of summer maize at late growth stage.2.In the two growing seasons of summer maize,compared with high nitrogen application rate and low nitrogen application rate,the stem diameter of 2-4 internodes at the base of stem increased by 1.6%-3.2%and 8.7%-10.5%,respectively,the plumpness increased by 13.4%-23.5%and 11.9%-14.5%,respectively,the breaking resistance increased by 9.1%-23.2%and26.9%-41.2%,respectively,the lodging resistance index increased by 19.6%-29.1%and 21.3%-25.6%,respectively,and the puncture force increased by 5.3%-13.8%and 20.2%-24.9%,respectively.The stem lodging resistance increased by 11.9%and 35.8%,respectively.Compared with NU treatment,the stem diameter,plumpness,breaking resistance,puncture resistance and stem lodging resistance of 2-4 internodes under CRNUNU treatment increased by 1.3%-16.2%,9.7%-47.7%,5.1%-28.6%,9.3%-25.3%,1.1%-15.1%and 8.1%-9.2%,respectively,and the internode length decreased by 4.1%-12.4%.3.In the two growing seasons of summer maize,compared with high and low nitrogen application rates,the lignin content in the basal 2-4 internodes of the stem was significantly increased by 19.9%-23.2%and 19.4%-25.7%,the cellulose content was significantly increased by 13.3%-44.1%and 10.2%-43.3%,and the hemicellulose content was increased by5.0%-8.5%and 3.2%-7.7%,respectively.The key enzyme activities（TAL,POD and PAL）of lignin synthesis were increased by 34.9%-45.2%,25.9%-30.2%,30.7%-33.6%and 26.5%-31.9%,14.1%-17.5%,29.9%-33.0%,respectively.Compared with NU treatment,the contents of lignin,cellulose and hemicellulose in basal 2-4 internodes of CRUNU treatment increased by 5.6%-14.3%,3.4%-28.1%and 1.2%-11.2%,respectively,and the activities of key enzymes（TAL,POD and PAL）for lignin synthesis increased by 4.4%-19.4%,2.1%-22.5%and 2.0%-14.9%,respectively.4.In the two growing seasons of summer maize,compared with low nitrogen application rate,the average root diameter increased by 27.0%and 20.3%,the root length increased by32.3%and 26.4%,the root surface increased by 32.3%and 30.8%,the root volume increased by 49.05%and 42.7%,and the root dry weight increased by 38.2%and 26.9%,respectively.There was no significant difference in root average diameter,root length,root surface and root volume between CRUNU treatment under high and medium nitrogen application rates.The root-pulling force increased first and then decreased with the increase of nitrogen application rate.Compared with high nitrogen application rate and low nitrogen application rate,the root-pulling force increased significantly by 12.1%and 39.5%under medium nitrogen application rate.Compared with NU treatment,the average root diameter under CRUNU treatment increased root length,root surface,root volume,root dry weight and root drawing force by0.6%-5.9%,14.6%-16.8%,10%-35.6%,9.3%-49.9%,1.3%-47.1%and 11.7%-15.9%,respectively.5.In the two growing seasons of summer maize,compared with high nitrogen application and low nitrogen application,the lodging rate of medium nitrogen application was significantly reduced by 58.5%and 39.6%,respectively.The yield increased with the increase of nitrogen application rate.Compared with low nitrogen application rate,high nitrogen application rate and medium nitrogen application rate increased ear diameter,ear length,ear row number,row grain number and 100-grain weight by 33.3%and 23.7%,respectively.There was no significant difference in yield between CRUNU treatment under medium nitrogen application rate and high nitrogen application rate.Compared with NU treatment,CRUNU treatment not only reduced the lodging rate（17%-14.0%）,but also significantly increased the ear diameter（3.7%-7.0%）,ear length（8.1%-12.9%）and 100-grain weight（6.0%-6.7%）of summer maize,thereby increasing grain yield（8.2%-16.8%）.In summary,the combination of controlled-release urea and conventional urea 1:1combined with medium nitrogen application rate(180 kg N·ha-1)can not only maintain the yield level of conventional nitrogen application rate(225 kg N·ha-1),,but also promote the accumulation of chemical components such as lignin,cellulose and hemicellulose in stems,improve the morphological characteristics and mechanical properties of stems,and optimize root structure（root average diameter increases root length,root surface,root volume,root dry weight and root pulling force）,thus effectively reducing the risk of lodging.The combination of the two can be used as a suitable fertilization mode in the summer maize planting system in Guanzhong area. |
