Effects Of Different Fertilization Depths On Plant Growth And Fruit Quality Of Blue Honeysuckle (Lonicera Caerulea L.)

Blue honeysuckle is an emerging cold-region small berry,mainly distributed in the northeastern,northern,and northwestern regions of China.It is mainly distributed in the Da Hinggan Mountains,Xiao Hinggan Mountains,and Changbai Mountain in the northeastern region.In recent years,with the increasing demand for blue honeysuckle,how to improve its yield and quality has become a bottleneck for its industrial development.Fertilization is an effective method to increase fruit tree yield,but the unreasonable fertilization methods in production reduce the utilization rate of fertilizers,cause a lot of waste,and affect the yield and quality of blue honeysuckle,which to a certain extent restricts the healthy and sustainable development of the blue honeysuckle industry.In the process of fruit tree fertilization,the depth directly affects the fertilizer utilization efficiency,and thus affects the fruit tree yield and fruit quality.Therefore,exploring reasonable fertilization depth has become the key to improving the yield and quality of blue honeysuckle.To investigate the effect of different fertilization depths on blue honeysuckle growth,a field experiment was conducted in Harbin,Heilongjiang from 2021 to 2022,using 5-year-old’Lan Jingling’blue honeysuckle as the experimental material.Under the same fertilization amount,five different fertilization depth treatments were set:no fertilization（F0）,5 cm depth fertilization（D5）,10 cm depth fertilization（D10）,15 cm depth fertilization（D15）,and 30 cm depth fertilization（D30）.By studying the effect of different fertilization depths on blue honeysuckle fruit yield and quality,plant growth and leaf photosynthetic characteristics,plant nutrient content and nutrient utilization efficiency,root distribution,and soil nutrient content,the following main research conclusions were obtained.（1）Effects of different fertilization depths on fruit yield and quality of blue honeysuckleAppropriate fertilization depth can increase fruit yield and promote the formation of fruit quality.Fertilization at a depth of 15 cm can effectively increase the yield and individual fruit weight of blue honeysuckle,with a yield of 9216.55 kg/hm²,which is 49.69%higher than that of surface fertilization at a depth of 5 cm.The optimal fertilization depth for the highest yield was found to be16.91 cm through fitting equations.The content of vitamin C,flavonoids,anthocyanins,and total phenols in the fruit reached its peak in the D15 treatment,and the fruit firmness and size also increased.However,the increase in sugar content also led to an increase in fruit acidity.As the fertilization depth further increased,the content of anthocyanins,vitamin C,flavonoids,and total phenols in the fruit also decreased.（2）Effects of different fertilization depths on growth and leaf photosynthetic characteristics of blue honeysuckleAppropriate fertilization depth can improve fruit yield and promote fruit quality formation of blue honeysuckle.Fertilization can promote plant height,canopy width,branch growth,and chlorophyll accumulation,increasing the photosynthetic capacity of blue honeysuckle.leaves,and provide a good material basis for fruit yield.When the fertilization depth is 15 cm,the plant height,canopy width,and new branch length growth increment of blue honeysuckle.are 21.87 cm,31.00cm,and 31.70 mm,respectively,which are significantly higher（P<0.05）than those of the control without fertilizer,with increases of 137.72%,91.00%,and 88.47%,respectively.The best effect of fertilization was observed at the depth of 15 cm,and the SPAD values were the highest in D15treatment at each stage,which were 25.82 and 44.32,respectively.The net photosynthetic rate of D15 treatment was 16.04μmol·m²·s^-1,which was increased by 35.93%,14.82%,6.30%,and 18.46%compared with F0,D5,D10,and D30 treatments,respectively.However,with the further increase of fertilization depth,the growth and development of blue honeysuckle were limited when the fertilization depth reached 30 cm.（3）Effects of different fertilization depths on nutrient content and nutrient utilization efficiency of blue honeysuckle plantsThe nutrient content of blue honeysuckle plants is related to the fertilization depth,and appropriate fertilization depth increases the nitrogen,phosphorus,potassium,and other nutrient content in branches,leaves,and fruits at different stages.The nutrient content of leaves and branches in the flowering period was higher than that in the fruiting period,and the nitrogen and phosphorus content in leaves was significantly higher than those in branches at both stages.The D15 treatment significantly affected the nitrogen,phosphorus,and potassium content of the plant and fruit,and was significantly higher than the 5 cm and 30 cm depth fertilization treatments（P<0.05）.The utilization efficiency of nitrogen,phosphorus,and potassium in blue honeysuckle fruits gradually increased and then decreased with the increase of fertilization depth,and the highest utilization efficiency was observed at a fertilization depth of 15 cm,which was 12.16%,6.27%,and 0.50%,respectively.Fertilization management at a depth near 15 cm could effectively promote the absorption and utilization of nutrients in branches,leaves,and fruits in blue honeysuckle.（4）Effects of different fertilization depths on root distribution and soil nutrient content of blue honeysuckleAppropriate fertilization depth can promote the growth of the root system of Indigofera tinctoria plants and facilitate the accumulation of available nitrogen,available potassium,and available phosphorus in different soil layers.The roots that absorb nutrients from Indigofera tinctoria are mainly distributed within 0-20 cm,with the largest number of roots,and the number of roots decreases with the vertical depth,with fewer roots at 40-60 cm.Treatment D15 increased the root length in the 0-20 cm soil layer by 30.14%,28.07%,and 83.20%compared to treatments D5,D10,and D30,respectively.Treatment D15 had a greater effect on the accumulation of available nitrogen,available phosphorus,and available potassium in the 0-20 cm soil layer,while treatment D30 had the greatest effect on the accumulation of available nitrogen,available phosphorus,and available potassium in the deeper 20-40 cm and 40-60 cm soil layers.Fertilization at a depth that is too deep can cause nutrient leaching downwards.In summary,applying fertilizer at a reasonable depth（15 cm）can increase the yield of blue honeysuckle fruit and improve its fruit quality,promote the growth of blue honeysuckle plants and their leaf photosynthetic characteristics,enhance the plants’photosynthetic capacity,increase the nutrient content of the blue honeysuckle trees,improve the distribution of roots in different soil layers,and increase the utilization of nutrients in fruits.