| In this experiment,the sorghum variety Jiza 140 was used as the test material,and five nitrogen application rates were set,which were 0 kg/hm~2(N0),80 kg/hm~2(N80),160 kg/hm~2(N160),240 kg/hm~2(N240)and 320 kg/hm~2(N320),respectively.The effects of different nitrogen application rates on growth,photosynthetic characteristics of leaves,key enzyme activities of nitrogen metabolism,yield and nitrogen utilization rate of sorghum were analyzed,and the optimal nitrogen application rates were determined to obtain the highest yield,in order to provide theoretical basis for scientific fertilization and high and stable yield of sorghum in Jilin Province.The research results are as follows:1.The nitrogen application rate significantly affects the plant height and stem diameter of sorghum during the filling period.The plant height increases with the increase of nitrogen application rate,and the stem diameter shows a trend of first increasing and then decreasing with the increase of nitrogen application rate,reaching the highest plant height and maximum stem diameter at 320 kg/hm~2and 160 kg/hm~2,respectively.2.Under the same nitrogen application rate,with the extension of the growth period,the leaf area index of sorghum first increases and then decreases,showing a single peak curve change,reaching its peak at the heading and flowering stage.When the nitrogen application rate was 160 kg/hm~2,the LAI was significantly higher than other treatments.With the increase of nitrogen application rate,the net photosynthetic rate of sorghum leaves fluctuated in a small range,and reached its maximum under N240 treatment.During the grouting period,the stomatal conductance continued to increase with the increase of nitrogen application rate under treatments not exceeding N240.The stomatal conductance weakened under N320 treatment,and there was no significant difference between N80 and N160 treatments.Overall,there was no significant difference between the concentrations of intercellular carbon dioxide.The highest concentration of intercellular carbon dioxide was observed under N160treatment.The transpiration rate reached its maximum under N80 treatment.3.Too high or too low nitrogen levels can affect the enzyme activity of nitrogen metabolism.During the jointing and filling stages,leaf nitrate reductase(NR)was the highest under the nitrogen fertilizer application rate of 160 kg/hm~2.The activities of glutamine synthetase(GS)and glutamate dehydrogenase(GDH)were different at different growth stages.The highest activity was found in the treatment of 160kg/hm~2at joint stage and the highest activity in the treatment of N80 at grout stage.The activity of glutamate synthetase(GOGAT)in leaves at jointing stage was the highest under N240 treatment.When the amount of nitrogen fertilizer application continues to increase,the enzyme activity significantly decreases.4.With the increase of nitrogen application rate,nitrogen partial productivity decreased,nitrogen utilization rate and nitrogen contribution rate increased first and then decreased.A higher nitrogen application rate has a significant inhibitory effect on the agronomic utilization efficiency of nitrogen fertilizer,with the best effect under the 160 kg/hm~2treatment.This indicates that the appropriate nitrogen application rate has a positive impact on the agronomic utilization efficiency of nitrogen fertilizer.At the same time,as the nitrogen application rate increases,the contribution rate of nitrogen fertilizer also significantly increases.The nitrogen fertilizer partial productivity gradually decreases with the increase of nitrogen application rate,and the nitrogen fertilizer partial productivity is the lowest under the treatment of 320 kg/hm~2.5.Dry matter accumulation increased with the increase of nitrogen application rate.Dry matter accumulation at seedling stage to jointing stage was small,and there was no significant difference among treatments(P>0.05).During jointing-flowering-grouting stage,sorghum grew vigorously and dry matter accumulation increased significantly.The accumulation of dry matter in N160 treatment reached the highest value during flowering and grouting stage.There was no significant difference between N320 treatment and no nitrogen treatment in the average dry matter accumulation in two years(P>0.05).With the increase of nitrogen application rate,sorghum yield increased gradually,but not linearly.Based on two years’data analysis,the highest yield under N240 treatment was 7543.5kg/hm~2(2021)and 7745.3kg/hm~2(2022),which was not significantly different from that under N320 treatment,but significantly higher than that without nitrogen application.The results of this study showed that the suitable nitrogen application rate significantly enhanced the agronomic characters of sorghum and improved the agronomic utilization rate of nitrogen fertilizer in the process of sorghum planting.According to the analysis of the above research results,when the nitrogen application rate is 267.29~2,it has positive effects on the key enzymes of nitrogen metabolism in sorghum leaves,photosynthetic characteristics and the improvement of sorghum yield. |
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