Effects Of Different Nitrogen Application Levels On Agronomic Traits And Physiological Characteristics Of Yunma No.8

Nitrogen is one of the essential nutrients for crop growth and development,and plays an important role in crop growth and material transformation,directly affecting crop growth and final yield.As a traditional fiber crop,hemp has extremely high economic,medicinal and ecological value.In this paper,Yunma No.8 was used as the test material,planted in the field,and 4 nitrogen supply levels（N0,N10,N20,N30,where N10 is low nitrogen level,N20 is medium nitrogen level,and N30 is high nitrogen level）were set,and urea was applied to the rhizosphere of 0kg/hm2,150kg/hm²,300kg/hm²,450kg/hm²respectively,the effects of different nitrogen application levels on the agronomic and physiological characteristics of hemp"Yunma No.8"were analyzed,so as to explore the effects of different nitrogen supply levels on the agronomic and physiological characteristics of hemp under field planting,identify the suitable nitrogen supply level of the tested hemp variety"Yunma No.8",and achieve high-quality and high-yield cultivation of hemp.The main results are as follows:1.There are differences in the agronomic characters of Yunma No.8 under different nitrogen supply levels.From seedling stage to early growth stage,the overall trend of agronomic traits of Yunma No.8 under different nitrogen supply levels showed that with the increase of nitrogen supply level,plant height,stem diameter,fresh weight,dry weight,and root-shoot ratio all showed an upward trend.Among them,the maximum plant height was257.6cm in the N20 treatment,the maximum stem diameter was 13.56mm in the N30treatment,and the plant dry weight and the root-shoot ratio were 167.89g and 14.82%in the N30 treatment,respectively.In the mature stage,stem diameter,fresh weight,dry weight and root-shoot ratio of hemp increased with the increase of nitrogen supply level,but the plant height under high nitrogen level was worse than that under medium nitrogen level.2.The physiological indexes of Yunma No.8 had different responses to different nitrogen supply levels.The content of malondialdehyde（MDA）in leaves reached the highest of 65.56nmol/g without nitrogen supply.Nitrogen application would slow down the senescence of hemp leaves to a certain extent,which showed that under low nitrogen level,the content of malondialdehyde in leaves was the lowest;reasonable nitrogen application can improve the peroxidase activity（POD）in leaves.The POD activity reached the highest level of 1344.84 U/（g·min）under the medium nitrogen level,and the activity was the weakest without nitrogen supply.The soluble protein content of leaves（BCA）and nitrate reductase activity（NR）in the whole growth period showed that,with the increase of nitrogen supply level,the BCA content and NR reached the maximum of 55.68（mg/m L）,4.4U/（g·min）;the nitrogen content of each organ generally increased with the increase of nitrogen supply level,while the phosphorus content decreased.3.There were differences in soil nutrient content as well as nitrogen and phosphorus content of each organ under different nitrogen supply levels.Specifically,the contents of soil alkali-hydrolyzable nitrogen and available potassium decreased under no nitrogen and high nitrogen treatments,and the contents of various soil nutrient indexes increased under low nitrogen and medium nitrogen conditions;the nitrogen content of each organ of Yunma No.8generally increased with nitrogen supply.The nitrogen content of each organ showed the order of leaf>stem>root,the root system obtained the maximum content of 10.42 g/kg^-1during the flowering stage,the stem obtained the maximum content of 14.99 g/kg^-1during the rapid growth stage,and the leaf obtained the maximum content of 14.99 g/kg^-1.The maximum content of 49.38 g/kg^-1was obtained at the bud-seeing stage,while the phosphorus content decreased under high nitrogen conditions.The overall expression of phosphorus content in each organ was leaf>root>stem;nitrogen accumulation showed the order of N20>N30>N10>N0,among which the root system obtained the maximum accumulation of 83.9 mg/plant at the flowering stage,and the stem and leaf obtained the maximum accumulation of 735.1 and 1567.1 mg/plant at the mature stage,respectively.The nitrogen absorption and utilization of Yunma No.8 was the best in N20 treatment,and the absorption and utilization in the flowering period reached the maximum value of 65.46%in the whole growth period.4.There are differences in the photosynthesis parameters of leaves of Yunma No.8under different nitrogen supply levels.In different periods,each parameter showed a trend of increasing first and then decreasing with the increase of nitrogen supply level,and each parameter reached the maximum value at medium nitrogen level.With the change of time,the photosynthetic parameters changed.The net photosynthetic rate（Pn）,transpiration rate（Tr）,intercellular CO₂concentration（C_i）,and stomatal conductance（Gs）all reached their maximum values in the bud-seeing stage.Water use efficiency（WUE）reached its maximum value at flowering stage,and there was a significant positive correlation between the parameters except WUE.5.The responses of chlorophyll fluorescence parameters of Yunma No.8 to different nitrogen supply levels were different.Among them,each parameter in different periods showed a trend of increase first and then decrease with the increase of nitrogen supply level,and each parameter reached the maximum value at medium nitrogen level.The initial fluorescence（F_O）and the maximum fluorescence（Fm）obtained the maximum value at the bud-seeing stage.The relative electron transfer efficiency（ETR）,reached the maximum value at the flowering stage,while the maximum photochemical efficiency（Fv/Fm）achieved the maximum value in the rapid growth period;except for WUE,the correlation between gas exchange parameters and chlorophyll fluorescence parameters of Yunma 8 leaves was good in different growth cycles.To sum up,the nitrogen supply level will affect the agronomic traits,physiological characteristics and photosynthetic parameters of hemp.Nitrogen levels will bring stress effects to hemp plants,causing them to fail to grow normally or grow ineffectively.A reasonable increase in nitrogen fertilizer can effectively improve the growth of hemp and increase the final yield to a certain extent.