Effects of application frequency of organic fertilizer extract and irrigation amount on the content of aromatic substances and cellulose in melon fruits

Objectives The extraction solution of organic fertilizer is the form of realizing organic fertilizer application with water irrigation. The effects of irrigation frequency and irrigation amount on the quality of melon fruit were studied to provide technical support for the production of high quality and high yield organic melon.

Methods The melon plot experiment used the method of fertilizing with drip irrigation. The extracts of organic fertilizer were extracted with mixing pig manure, cattle manure and sheep manure with water in a ratio of 1∶10 for 72 h, and then filtered. The three filtrates were mixed in a ratio of 4∶1∶1 by volume and diluted by 4.3 times for melon fertilization. The experiment set up three irrigation frequency of organic fertilizer extract: 8 times of application, 750 mL per plant (F₁); 12 times of application, 500 mL per plant (F₂); 16 times of application, 375 mL per plant (F₃). There were two levels of irrigation: W₁ was 120% of the daily evapotranspiration before fruit expansion, and then 140% of the daily evapotranspiration. W₂ was 140% and 160% of the daily evapotranspiration. SPME-GC-MS was used to determine the volatile components, relative content and cellulose content of melon fruit after ripening.

Results A total of 71 volatile components were detected in melon fruits, and the order of total content was F₂W₂ > F₁W₁ > F₃W₁ > F₁W₂ > F₃W₂ > F₂W₁. Among the six treatments, there were 21 kinds of volatile substances, and the order of their contents from high to low was the same as that of the total volatile substances. Under W₁, the content of characteristic aroma substance in fruit was the highest in F₁, while under W₂, its content first increased and then decreased with the increase of irrigation frequency of organic fertilizer extract, which was opposite to the former. Under the same irrigation frequency of organic fertilizer extract, the change rule was not obvious. Among them, F₂W₂ treatment had the highest content of characteristic aroma substances, which was significantly higher than other treatments, indicating that the irrigation frequency of medium and high irrigation amount were beneficial to the formation of characteristic aroma in melon fruit. Under the condition of low irrigation amount, with the increase of irrigation frequency of organic fertilizer extract, the cellulose content of fruit increased first and then decreased; under the condition of high irrigation amount, the cellulose content of fruit increased. With the increase of irrigation amount, the cellulose content of fruit decreased significantly. Among them, the cellulose content of melon fruit treated with F₂W₁ was the highest, which was 1.3 mg/g, 8.3%–227.5% higher than other treatments. The content of aromatic substance and cellulose in melon fruit was evaluated by membership function method. The comprehensive ranking order was F₂W₂ > F₁W₁ > F₃W₁ > F₃W₂ > F₂W₁ > F₁W₂. The yield of muskmelon treated with F₂W₂ was the highest, reaching 1.8 kg/m².

Conclusions The effect of irrigation frequency and irrigation amount of different organic fertilizer extracts on the volatile matter and content of melon fruit is consistent with the effect on the characteristic aroma components and content of melon fruit. Under the condition of this experiment, F₂W₂ treatment is the optimal in which the aromatic matter content, cellulose content and yield of melon fruit reach their most satisfying degree.