Effects Of Nitrogen Reduction Combined With Polyaspartic Acid On Nitrogen Metabolism,absorption And Utilization Of Flue-cured Tobacco

In order to explore the effect of polyaspartic acid（PASP）on nitrogen metabolism and absorption and utilization of flue-cured tobacco under the condition of nitrogen reduction,taking“Yunyan87”as the test material,the local nitrogen application rate(142.5kg·hm^-2)was used as a control,and under the condition of reducing the nitrogen application rate by10%(128.25 kg·hm^-2),five treatments（CK,NP0,NP1,NP2,NP3）were set with different PASP dosage as variables.The trial was conducted at Xinxu Tobacco Workstation in Xintian County,Yongzhou City,Hunan Province in 2019.Through the comparison and analysis of agronomic characters,key enzyme activity of nitrogen metabolism,SPAD value,photosynthesis,dry matter accumulation,nitrogen and potassium absorption,chemical composition of flue-cured tobacco leaves,economic characters,nitrogen utilization rate and nitrogen balance of tobacco planting soil among different treatments,the effects of reducing nitrogen and applying PASP on nitrogen metabolism,photosynthetic characteristics and nitrogen absorption and utilization of flue-cured tobacco were discussed.It can provide a reference for reducing nitrogen and using PASP to improve fertilizer utilization and maintain soil nutrient balance in tobacco production.The main findings are:（1）10%nitrogen reduction had no significant effect on the agronomic characters of flue-cured tobacco.NP2 with 5%PASP was significantly higher than CK in plant height,and the largest leaf area was higher than other treatments,but the difference was not significant.There was no significant difference in agronomic characters among other treatments.（2）Compared with the conventional nitrogen application rate,tobacco plants that reduced nitrogen by 10%had nitrate reductase（NR）,glutamine synthetase（GS）,glutamate oxaloacetate transaminase（GOT）,and alanine aminotransferase（GPT）Have a certain degree of decline,The application of PASP can increase 4 kinds of nitrogen metabolism-related enzymes.Among them,the activity of nitrogen metabolism-related enzymes is higher in NP2treatment when the amount of PASP is 5%of the nitrogen application.Compared with NP0treatment,the nitrate reductase activity of NP2 treatment has the highest increase.39.78%,glutamine synthetase activity increased by 53.38%～69.98%,glutamate oxaloacetate transaminase activity increased by 7.23%～12.90%,and glutamin transaminase activity increased by 42.15%at the maximum.The activity of nitrogen metabolic enzymes of NP1and NP3 also increased to a certain extent,but the increase was smaller than that of NP2.（3）The SPAD value of the treatment with a reduction of 10%in nitrogen application rate was lower than that of the control,and the SPAD value of the NP0 treatment before harvest was significantly lower than that of the CK.PASP application can increase the SPAD value of tobacco leaves to varying degrees.60 days after transplanting,the upper and middle leaves increased by 20.39%and 15.04%compared with NP0,respectively,and were 2.37%and 0.59%lower than CK.Different nitrogen application rates and different PASP dosages had a significant effect on the photosynthetic characteristics of the upper and middle leaves.The net photosynthetic rate of CK was higher than that of NP0,NP1,and NP3 treatments that reduced nitrogen application by 10%.The average rate is significantly higher than NP0.The difference between the average daily net photosynthetic rate of NP2 and CK is the smallest.The average daily net photosynthetic rate of the upper and middle leaves is increased by 3.02μmol·m^-2·s^-1 and 2.30μmol·m^-2·s^-1 compared with NP0.The intercellular CO2 concentration of the three treatments with PASP was higher than that of NP0,and NP2with 5%PASP was only 0.03%～5.72%lower than CK,but 6.54%～14.37%higher than NP0.The peak value of transpiration rate of each treatment appeared at 13:00,and CK had the highest transpiration rate.The transpiration rate of upper leaf and middle leaf were 4.82μmol·mol^-1 and 3.63μmol·mol^-1,respectively.The difference between NP2 treatment with5%PASP and CK was the smallest,only 12.03%and 27.25%lower than CK,while NP0 was25.09%and 18.07%lower than CK.（4）Nitrogen reduction of 10%had an adverse effect on the accumulation of dry matter,protein,and absorption of nitrogen and potassium in tobacco plants.Until harvest,the accumulation of dry matter,protein,and absorption of nitrogen and potassium in NP0decreased compared with CK 16.52%,15.63%,28.07%,16.11%.The dry matter accumulation of NP2 treated with 5%PASP was 5991.15 kg·hm^-2 80 days after transplanting,11.32%higher than CK;the protein accumulation was 628.65 kg·hm^-280 days after transplanting,higher than CK 13.33%;the total nitrogen uptake reached 100.59 kg·hm^-2 80days after transplanting,11.84 kg more nitrogen per hectare than the control;the highest potassium uptake treatment after 80 days was NP3,up to 146.58 kg·hm^-2,19.90%higher than the control,followed by NP2,an increase of 8.13%compared to the control.（5）Compared with CK,the total nitrogen content of NP0 treated leaves reduced by 10%decreased to a certain extent,and the upper leaves decreased by 0.25 percentage points.The total nitrogen content of the upper,middle and lower leaves of NP2 treatment with 5%PASP was higher than that of NP0 treatment,and was 0.07,0.05 and 0.07 percentage points higher than CK,respectively;the total potassium content of the upper leaves of NP0 was reduced compared with CK 6.13%,the total potassium content CK of NP1 and NP3 was 0.12percentage points higher.The middle and lower leaves performed similarly to the upper leaves.The middle leaves had the highest total potassium content of NP3,38.93%higher than CK,and the lower leaves had the highest total potassium content of NP2,reaching 1.66%,18.75%higher than CK.From the perspective of total sugar and reducing sugar,compared with CK,the total sugar content of NP0 treatment without nitrogen reduction 10%without PASP was higher than that of CK.Among them,the total sugar content of upper leaves was24.67%higher than CK,the difference was significant.The total sugar content of NP1,NP2and NP3 treated with PASP was mostly lower than that of CK.The nicotine content of each leaf position of NP0 treatment was lower than that of CK.The treatments with the highest nicotine content in the upper,middle and lower leaves were NP3,NP1 and NP2,which were36.64%,38.22%and 9.78%higher than CK,respectively.（6）In terms of economic traits,compared with CK,the output and output value of NP0treatment with a nitrogen reduction of 10%decreased by 13.91%and 14.47%,the average price decreased by 0.14 yuan·kg^-1,and the proportion of first-class smoke and the proportion of middle-upper grade smoke decreased.1.43 percentage points and 3.22 percentage points.The economic performance indexes of NP1,NP2 and NP3 in the treatment of nitrogen reduction and PASP application are higher than NP0,and the output and output value of NP2with 5%PASP is the highest,reaching 2573.34 kg·hm^-2,57165.40 yuan·hm^-2.It is 5.18%and 8.35%higher than CK;the average price of NP3 with 7.5%PASP is the highest,which is 0.69yuan·kg^-1 higher than that of the control;the proportion of NP2’s superior smoke is7.15%higher than that of CK The proportion of middle and upper grade smoke also increased by 1.70 percentage points compared with the control.（7）Compared with CK,NP0’s nitrogen fertilizer agronomic efficiency,nitrogen fertilizer production efficiency,seasonal recycling rate and economic utilization rate have declined to varying degrees.The nitrogen fertilizer utilization rate of the NP2 treatment with the same fertilization amount as NP0 and 5%PASP was the best among the five treatments.The agronomic efficiency of nitrogen fertilizer was increased by 20.83%compared with the control,the partial productivity of nitrogen fertilizer was increased by 16.86%,and the recovery rate of the season Increased by 21.05%,economic utilization increased by 37.16%.From the point of view of the nitrogen balance of tobacco-growing soil,the annual average nitrogen surplus of CK is 53.75 kg·hm^-2 and the balance rate is 60.56%,and the annual average surplus of NP2 is reduced to 27.66 kg·hm^-2 33.06 percentage points lower than CK.