Effects of deep slow-release fertilizer on melon yield, economic benefits and rhizosphere microorganisms

Simplified fertilization is a core technology for achieving efficient melon cultivation. However, the optimal application depth of slow-release fertilizers in the major melon-producing regions of Xinjiang remains poorly defined. In this study, field experiments were conducted to evaluate three application depths of slow-release fertilizer: 15 cm (SF15), 25 cm (SF25), and 35 cm (SF35). Conventional fertilization (CF; 20-25 cm) and a no-fertilizer treatment (F0) were included as controls to systematically investigate the effects of application depth on nutrient accumulation, yield, economic benefits and rhizosphere microbial communities of melon. The results showed that CF treatment primarily increased soil potassium content during the middle and late growth stages and promoted potassium accumulation in fruits, while enriching beneficial microbial taxa associated with carbon cycling and plant stress resistance. In contrast, the SF35 treatment significantly increased soil nitrogen and phosphorus contents and their accumulation in fruits during the same growth stages. This treatment also enriched nitrogen-cycling bacteria and phosphorus solubilizing fungus. In addition, SF35 consistently increased the ACE index of rhizosphere bacterial communities throughout the growth period and adjusted soil pH to a range more suitable for melon growth (6.07-6.62). Importantly, melon yield under SF35 were maintained at levels comparable to those under CF, while reducing labor costs and improving economic benefits. In conclusion, 35 cm is recommended as the optimal application depth of slow-release fertilizer for melon in Xinjiang. This practice enhances key functional microbial groups and soil physicochemical properties, while achieving yield and quality comparable to those of CF in a single application. The findings of this study can provide scientific support for the standardized application of simplified fertilization technology in Xinjiang melon production.