Effect Of Combined Application Of Nitrogen And Phosphorus Fertilizer On The Growth Of Fraxinus Velutina Torr. In Coastal Saline-Alkali Soil

Fraxinus Velutina Torr.has strong saline-alkali tolerance and stress resistance,and plays an important role in vegetation construction and soil improvement in coastal saline-alkali land.Therefore,it is of great significance to find out the optimal fertilization ratio of ash in coastal saline-alkali soil for its popularization and application.In this paper,the’3414’incomplete test scheme was used,nine optimal treatments were used,and the optimal nitrogen and phosphorus application rates were calculated by binary quadratic equation fitting.The effects of different nitrogen and phosphorus ratios on the growth of ash seedlings and saplings in coastal saline-alkali land were studied by field experiments and pot experiment.Field experiments were conducted to study the effects of different ratios of nitrogen and phosphorus on growth,physiology and rhizosphere soil characteristics of 3-year-old ash forest.A pot experiment was conducted to study the effects of different nitrogen and phosphorus ratios on the growth and physiological characteristics of 1-year-old cuttings of Luwa 2 and Yanwa 2.The test results are as follows:（1）Fertilization significantly promoted the growth of ash seedlings.With the increase of N content,the growth（seedling height,ground diameter,total biomass）,leaf nitrogen and phosphorus content,photosynthetic physiology（total chlorophyll,stomatal conductance,intercellular CO₂concentration,transpiration rate）,root characteristics（total root volume,root average diameter）of ash seedlings and saplings increased first and decreased,and the highest was at 2 levels.With the increase of P application rate,the growth（seedling height,ground diameter,biomass）,leaf nitrogen and phosphorus content,photosynthetic physiology（total chlorophyll,stomatal conductance,transpiration rate）,root characteristics（total root length,total root volume,root average diameter）of ash seedlings and saplings increased first and then decreased,and the highest was at 2 levels.In different nitrogen and phosphorus ratio,2:1 had good effect on seedling;2:3 has good effect on young trees,and the optimal ratio is between 2:1 and 2:3.With the increase of fertilizer application,the growth（seedling height,ground diameter,biomass）,photosynthetic physiology and root characteristics of ash seedlings and saplings increased significantly.Correlation analysis showed that seedling height and ground diameter growth were significantly positively correlated with chlorophyll content,leaf total phosphorus and root characteristics（total root length and root mean diameter）.（2）Fertilization can improve the rhizosphere soil characteristics of ash saplings.Among them,N had the greatest effect on the content of hydrolyzable nitrogen and available phosphorus,but the effect of nitrogen fertilizer alone was not obvious.P fertilizer had the greatest impact on soil urease and soil phosphatase activities.When the nitrogen fertilizer application rate was 0.060～0.090 kg and the phosphorus fertilizer application rate was 0.020～0.040 kg,the content of hydrolyzable nitrogen and available phosphorus in the soil of forest land was the most significantly increased.When the amount of nitrogen fertilizer was 0.030～0.060 kg and the amount of phosphorus fertilizer was 0.040～0.060 kg,the activity of urease and phosphatase in soil was the highest.（3）Among the nine treatments with different ratios of nitrogen and phosphorus,N₂P₂treatment had the best effect on the growth of young trees and seedlings,so N₂P₂treatment had the highest effect on the growth of young trees and seedlings.For seedlings,the effect is greater when the ratio of nitrogen and phosphorus is 2:1.For young trees,the effect is greater when the ratio of nitrogen to phosphorus is 2:3.When the ratio of nitrogen and phosphorus was 1:1,the promotion effect increased with the increase of total fertilization.Overall comparison shows that N2P2 treatment is the best ratio to promote the growth of ash.Through the binary quadratic equation fitting calculation of’3414’fertilization scheme,the optimal nitrogen application rate was 0.045 kg/plant and the optimal phosphorus application rate was 0.025 kg/plant.（4）The growth indexes of Luwa No.2 and Yanwa No.2 were compared.Luwa No.2was superior to Yanwa No.2 in root development,leaf total nitrogen content and chlorophyll content.Therefore,the adaptability of Luwa No.2 was superior to Yanwa No.2.