Effects Of NPK Fertilization On Polyphenol Oxidase Activity And Curing Effect In Flue-cured Tobacco

Nitrogen,phosphorus and potassium are the three important nutrient elements in the growth process of flue-cured tobacco.The growth of tobacco leaves is different under different fertilizer supply,and there are differences in curing characteristics and tobacco leaf quality.Polyphenol oxidase(PPO),as a key enzyme in the oxidative browning reaction,is essential for the curing quality of tobacco leaves.The effects of different fertilizer supply on PPO activity and curing quality of tobacco leaves were studied,which provided a theoretical basis for the quality of tobacco leaves.In this experiment,flue-cured tobacco NC102 was used as research material,and different nitrogen,phosphorus and potassium fertilizer dosages were set.The agronomic traits,PPO activity,chemical composition and quality of roasted tobacco leaves were measured and analyzed.The test results are as follows:(1)When the application rate of nitrogen fertilizer was higher than 5 g/pot,the PPO activity of tobacco leaves in all parts of the flue-cured tobacco remains high during the maturity and curing process.Below the fertilization level,the PPO activity of the middle and lower tobacco leaves during the curing process was significantly lower than other treatments,while the PPO activity of the upper tobacco leaves was not significantly reduced;in terms of chemical composition,as the nitrogen supply increased,the total nitrogen,total potassium and nicotine content of tobacco leaves increased,the sugar content decreased.And when the dosage was 3.75 g/pot,the chemical composition of tobacco leaves is the most coordinated.As the amount of nitrogen increases,the irritancy of the tobacco leaves increases.The increase of nitrogen application rate can promote the increase of plant height,maximum leaf area,number of leaves and stem circumference.Under the conditions of this test,the amount of nitrogen was the best at 3.75 g/pot.(2)With the increase of the amount of phosphate fertilizer,the PPO activity of the lower fresh tobacco leaves increased gradually,and the PPO activity of the middle and upper fresh tobacco leaves increased first and then decreased;The PPO activity in the early stage of curing was kept low,when the phosphorus application was less than 7.5 g/pot,and the high phosphorus application had no effect on the PPO activity of the tobacco leaves.With the increase of the amount of phosphate fertilizer,the total phosphorus content in tobacco leaves increased significantly,and the total nitrogen,total potassium and sugar also increased in different degrees,and nicotine decreased slightly.Under the conditions of this experiment,the agronomic traits of tobacco plants were better,and the chemical composition of tobacco leaves was coordinated,when the phosphorus was applied at 12.5 g/pot.(3)With the increase of potassium fertilizer application,the PPO activity of the lower fresh tobacco leaves increased gradually,and the PPO activity of the middle and upper fresh tobacco leaves gradually decreased.When the potassium dosage reached 20g/pot,the PPO activity of the upper middle tobacco leaves was lower during the curing process.The PPO activity of the lower leaves was also significantly lower than other treatments at the peak;with the increase of potassium fertilizer,the total potassium and sugar content increased,the total nitrogen and nicotine content decreased,and the chemical composition was best at 20 g/pot.The increase of potassium application rate has a certain promoting effect on the plant height,leaf number,maximum leaf area and stem circumference of flue-cured tobacco.Under the conditions of this experiment,the amount of potassium at 20 g/pot is most favorable for tobacco leaf production.