Enhancing passion fruit (Passiflora edulis f. flavicarpa Degener) agriculture with application of alkaline humic acid fertilizer and chemical fertilizer: A effective approach to soil and fruit quality optimization

Agricultural practices like continuous cropping and excessive chemical fertilization contribute to soil nutrient depletion, adversely affecting the quality and yield of passion fruit. To sustainably enhance soil quality and ensure the quality of passion fruit, this study investigates the combined application of alkaline humic acid fertilizer (AHF) and chemical fertilizer (CF) in passion fruit cultivation on a field that had been continuously cultivated for two years. We observed that the 55 % CF + AHF treatment (a 45 % reduction in CF with AHF) significantly improved soil nutrient content compared to the 100 % CF treatment, resulting in increases of 112.9 % in available nitrogen (AN), 107.9 % in available phosphorus (AP), and 446.2 % in available potassium (AK). This treatment also maintained soil conductivity and trace mineral stability while enhancing several fruit quality indicators, including a 40.4 % increase in fruit yield, as well as improvements in the sugar/acid ratio, vitamin C (VC) content, and amino acid levels. Furthermore, metabolomics analyses indicated that the 55 % CF + AHF group was enriched in functional small molecules, such as piceatannol, isoorientin, phytosphingosine, oligopeptides, and flavor-related compounds. Conversely, higher rates of CF application were associated with significant reductions in three functional oligopeptides levels. Therefore, this underscores AHF's critical role as a supplement for reducing CF usage while mitigating negative effects from continuous passion fruit cultivation. Thus, the 55 % CF + AHF treatment may represent a viable strategy to sustainably improve soil quality and ensure the quality of passion fruit while also contributing to a more sustainable agricultural system. • Chemical fertilizer (CF) was substituted by alkaline humic acid fertilizer (AHF). • Improved soil AN, AP, and AK contents proved 55 %CF+AHF sustainability. • The yield in the 55 %CF+AHF treatment increased by 40.4 %. • 55 %CF+AHF maintained a high sugar-acid ratio, VC and amino acid content in fruit. • 55 %CF+AHF enhanced functional and flavor-related metabolomic compounds.