<p>Conventional tillage in onion cultivation degrades physical, chemical and biological properties of soil. In response, the no-tillage vegetable system (NTVS) is increasingly recognized as efficient conservationist cropping system for onion cultivation. To determine how distinct crop successions combinations optimize soil functioning, this study evaluated a long-term organic NTVS experiment comprising eight treatments of winter (black oat, oilseed radish, or fallow) and summer crops (velvet bean, soybean, millet, common bean, or maize) succession combinations for onion production. This study assessed cover crop mulch, onion yield, soil fertility, and enzyme activities (FDA hydrolysis, arylsulfatase, and β-glucosidase). Results showed that the organic NTVS improved soil fertility, increasing organic matter by 38% (0–10&#xa0;cm) and 13% (10–20&#xa0;cm) compared to previous evaluations. Successions with black oat maximized mulch production, while successions combining black oat in winter with legumes (velvet bean, soybean) in summer maximized onion yield (up to 34.7&#xa0;Mg·ha⁻¹). Enzyme activity was influenced by crop development stage and succession combination; FDA hydrolysis peaked at 361&#xa0;μg fluorescein·g⁻¹·h⁻¹ during onion bulbification, and arylsulfatase consistently exceeded 114&#xa0;μg p-nitrophenol·g⁻¹·h⁻¹ across treatments. A principal component analysis confirmed that enzyme activity was regulated by crop succession combination rather than fertility attributes. In conclusion, combining winter grasses or crucifers with summer legumes optimizes soil enzyme activity, fertility attributes, and onion performance in long-term organic NTVS.</p> Graphical Abstract <p></p>