Effects Of Different Potassium Application Rates On Growth And Fruiting Of Protected Peach

Peach（Prunus persica L.）originated in China and has a long cultivation history and rich cultural connotation.Its fruit is juicy,sweet in taste,and rich in a variety of mineral nutrients.Both fresh and processed peaches occupies an important position in the fruit market.The cultivation technology of protected peach has been widely adopted,and the ripe fruit can be put on the market 2-3 months earlier,which presents a promising market potential.However,there are challenges in achieving desired sweetness and taste of fruits under protected cultivation.On the one hand,it is related to the protected environment with weak light,low concentration of CO₂and high temperature and humidity.On the other hand,inadequate application of potassium fertilizer,and insufficient attention to potassium usage during cultivation and management are also the main reason.This study focused on three-year-old protected peach trees and conducted experiments during the fruit expansion stage.Two groups of treatments were established:single potassium fertilizer and a mixture of nitrogen,phosphorus,and potassium fertilizer（The application ratio of nitrogen and phosphorus fertilizer was1:0.5）.According to the ratio of 0:0.5:1:1.5:2,five levels of potassium fertilizer were applied to explore the effects of different potassium application rates on peach growth,appearance quality,internal quality,photosynthetic characteristics,nutrient content in branches and leaves,yield,and economic benefits.By comparing the differences among the various fertilization treatments,the optimal potassium application rate was determined,providing theoretical guidance for future peach cultivation.The main results of the experiment are as follows:1.Fruit QualityPotassium fertilizer had significant effects on appearance and internal quality of protected peaches.Fruit coloring was improved significantly after potassium application,and fruit weight increased significantly（9.95%）under high potassium concentration in mixed application group.In terms of internal quality,potassium fertilizer significantly reduced titrable acid content,increased soluble solid,soluble total sugar and soluble protein contents,and significantly increased the contents of glucose,fructose,sucrose and sorbitol at maturity stage,while significantly decreased malic acid,tartaric acid and citric acid contents.The contents of mineral elements（N,K,Ca,Mg,Fe,Mn,Zn）in fruits significantly increased under single potassium application of 202 g/plant.Overall,the fruit quality of protected peaches treated with single potassium fertilizer at 202 g/plant and mixed potassium fertilizer at 269 g/plant showed significant improvements compared to the control.2.The growth of the plantPotassium application had significant effects on photosynthetic characteristics and mineral elements content in branches,leaves and surrounding soil of peach trees.The single application of 135g potassium fertilizer per plant increased the leaf area,the contents of chlorophyll a,chlorophyll b and chlorophyll a+b by 13.65%,14.63%,10.44%and 13.61%,respectively.Under the mixed application of nitrogen,phosphorus and potassium,chlorophyll content increased significantly with the application of 67g potassium fertilizer per plant,but leaf area did not show a significant increase.The maximum photosynthetic rate and transpiration rate increased by 14.78%,42.27%and 13.39%,25.15%compared with the control under the treatment of 202g potassium fertilizer alone and 269g potassium fertilizer mixed with nitrogen and phosphorus fertilizer.In the mixed application group,stomatal conductance（Gs）significantly increased after fertilization,reaching a maximum under 269g potassium fertilizer,while intercellular carbondioxide concentration（Ci）decreased significantly.In the single application group,Ci also decreased significantly under the treatment of 135 g/plant and 202 g/plant.The results demonstrated that the photosynthetic rate and transpiration rate significantly increased under the treatment of 202 g/plant for potassium fertilizer and mixed potassium fertilizer at 269 g/plant,indicating improved photosynthetic characteristics in peach trees.The content of mineral elements in leaves and branches increased to different degrees under the treatment of appropriate potassium fertilizer,and the content of mineral elements in the soil increased more obviously in the 20-40cm soil layer after fertilizer application.3.Plant yield and economic benefitThe yield and economic benefit increased obviously after potassium fertilizer application.With single potassium fertilizer application,the yield and economic benefit per plant initially increased and then decreased with the increase of potassium application amount,and the maximum yield and benefit per plant were 6.26 kg/plant and 43416.49 yuan/mu under 135g potassium fertilizer per plant,followed by 202g/plant（5.91 kg/plant and 40715.71 yuan/mu）,and there was no significant difference between them.In the mixed application group,the highest yield（6.64 kg/plant）and benefit（45367.16 yuan/mu）were obtained from 269g potassium fertilizer per plant,and the yield was significantly increased by 43.15%compared with the control group.There was no significant difference in yield and economic benefit among the three treatments.In conclusion,the fruit quality,photosynthetic characteristics,yield and economic benefits of protected peach were significantly improved by single potassium application of 202 g/plant and mixed potassium application of 269 g/plant.However,when mixed application of potassium fertilizer 269 g/plant,fruit weight,yield and economic benefits are higher,and titrable acid and citric acid contents are significantly lower.Therefore,the effect of mixed application of potassium fertilizer269 g/plant is better,and the application amount of this treatment can be used as a reference for fertilization.