Effects of alginate water soluble fertilizer and fulvic acid water soluble fertilizer on tree growth and fruit quality of Fuji apple

Abstract：【Objective】Effects of alginate water soluble fertilizer and fulvic acid fertilizer on root growth, leaf growth and fruit quality of Fuji apple with M9T337 rootstock were studied, and their application effects were evaluated.【Methods】Using 5- year- old Aztec Fuji trees with M9T337 dwarfing rootstock as materials, apple trees were treated with compound fertilizer (CK), equal amount of NPK alginate water soluble fertilizer (AF) and equal amount of NPK fulvic acid water-soluble fertilizer (FF). The roots were monitored by CI- 600 root in- situ monitoring system, and the root growth, the leaf growth and fruit quality were measured. Three treatments were designed, CK (compound fertilizer), AF (alginate water soluble fertilizer) and FF (fulvic acid water-soluble fertilizer). Three repeats were set for each treatment, a single plant as a plot, a total of 9 plants. The fertilizeres for all treatments were applied in three times: before flowering (March 20th), young fruit stage (May 20th) and fruit expansion stage (July 20th). The input of nitrogen, phosphorus and potassium in each period was 40%, 30% and 30% of the annual input, respectively. The water-soluble fertilizer treatment adopted the integrated fertilization technology of water and fertilizer with simple device, consistently with other field management. WinRHIZO Tron MF 2019 analysis software was used to process the collected images and obtain rele-vant root data. According to the vertical position of the soil, each picture was divided into four layers: 0- 20 cm, 20-40 cm, 40-60 cm and 60-80 cm. The roots in each soil layer were described respectively, and the length, average width, surface area, volume and other parameters of the root system were analyzed. The relative chlorophyll content was measured by SPAD- 502 chlorophyll meter. The leaf area was measured with a leaf area meter LI-3000C. The photosynthetic index was measured by CIRAS-3 portable photosynthetic instrument of PP system. The leaf fresh weight was weighted by an electronic balance. After weighing, the leaves were put into an oven at 105 ℃ for 15 minutes, and then dryed in an oven at 80 ℃ to constant weight. After 48 hours, the dry weight of hundred leaves were measured. The single fruit weight was measured by balance. The fruit shape index was measured with vernier caliper. The soluble solids were measured by Atago-pal-1 digital sugar meter. The fruit hardness was measured by GY-1 fruit hardness tester. The Vitamin C content was determined according to GB 5009.86—2016. The titratable acids were determined by GMK-835N fruit acidity meter. L, a and b were measured by NR60CP, and the measured data at 3 points were taken as the average value. The Excel was used to sort out the test data and plot, SPASS 22.0 was used for analysis of variance.【Results】Both the alginate water soluble fertilizer and fulvic acid water soluble fertilizer could promote root growth. The root length density of the alginate water soluble fertilizer treatment was 300% higher than that of the control and 145% higher than that of the fulvic acid water soluble fertilizer. The root surface area density growth of the alginate water soluble fertilizer treatment was 245% higher than that of the fulvic acid water soluble fertilizer. The root number density growth of the alginate water soluble fertilizer treatment was 267% higher than that of the control and 57.14% higher than that of the fulvic acid water soluble fertilizer. The fulvic acid water soluble fertilizer was the largest increase in average root diameter growth, followed by the alginate water soluble fertilizer and CK. The relative chlorophyll content, hundred leaf fresh weigh, hundred leaf dry weight, fruit weight, fruit shape index, soluble solids, solid acid ratio and vitamin C content in different fertilization treatments were higher than those of the control. The fruit weight of the alginate water soluble fertilizer and fulvic acid water soluble fertilizer treatment was 16.86% and 12.00% higher than that of the control, respectively; the soluble solids were 4.35% and 3.59% higher than that of the control, respectively; The solid acid ratio was 0.97% and 31.55% higher than that of the control, respectively; The content of vitamin C was 12.74% and 21.66% higher than that of the control, respectively. The different fertilization treatments also improved the peel coloring to varying degrees. The principal component dimension reduction analysis was used to evaluate the comprehensive effect. The comprehensive effect from high to low was: AF＞FF＞CK. The image analysis showed that the two fertiliers had a good measurement effect on the apple root growth.【Conclusion】 Both the alginate water soluble fertilizer and fulvic acid water soluble fertilizer increased the content of nutrients in the soil, promoted the root growth of Fuji apple, increased the SPAD, net photosynthetic rate and dry matter content in the leaves, improved the fruit quality, and the skin color of Fuji apple to varying degrees. The comprehensive effect of the alginate water soluble fertilizer was better than that of the fulvic acid water soluble fertilizer. The CI-600 root in situ monitoring system performed well in apple root observation, and could be used for root related research for apple trees.