Organic-Inorganic Substitution Improves Cucumber Yield and Quality by Enhancing Carbon and Nitrogen Metabolism in Cucumbers

Replacing chemical fertilizers with organic fertilizers can improve soil quality and continuously increase crop yields, but its impact on cucumber growth remains unclear. This study, based on a seven-year field trial, explored the effects of five different fertilization strategies: no fertilization, application of inorganic fertilizer (NPK), 2/3 NPK + 1/3 organic fertilizer (M), 1/3 NPK + 2/3 M, and M on cucumber carbon and nitrogen metabolism, antioxidant levels, yield, and quality. The results showed that both NPK and M applications were beneficial to improving cucumber yield and quality. However, NPK alone led to the accumulation of malondialdehyde (MDA) in leaves, while NPK + M could improve its total antioxidant capacity. Furthermore, 1/3 NPK + 2/3 M significantly promoted the accumulation of amino acids and glucose in leaves and increased the activities of glutamine synthase, sucrose phosphate synthase, and other enzymes. Further analysis revealed that the content of glucose and protein in leaves was closely related to the synthesis of soluble sugars and vitamin C in fruits, with sucrose and MDA showing the most significant effects from different fertilization strategies. In conclusion, the application of 1/3 NPK + 2/3 M significantly improved the carbon and nitrogen metabolism activity of cucumbers, enhanced their stress resistance, and promoted yield and quality.