Abstract:

Flowering Chinese cabbage (Brassica campestris ssp. chinensis var. utilis) is the most widely cultivated specialty vegetable in southern China. Currently, excessive nitrogen (N) fertilizer application and insufficient magnesium (Mg) is serious obstacle to the green and efficient production of flowering Chinese cabbage. This study designed a nitrogen-magnesium synergistic fertilizer product and conducted field trials in 2023 on the use of magnesium-containing nitrogen fertilizers as a substitute for compound fertilizers. The following treatments were set up: no N fertilizer control (CK), urea alone (T1), farmers' customary treatment (T2, 15-15-15-0 compound fertilizer), N and Mg synergistic fertilizer (26-0-0-2) replacing 50% of the farmers' customary compound fertilizer (T3), and replacing 100% of the farmers' customary compound fertilizer (T4). The differences in agronomic traits, yield, quality, nutrient absorption, and utilization efficiency of flowering Chinese cabbage during the seedling and maturity stages were investigated. The results showed that during the seedling stage, both T3 and T4 treatments significantly increased the biomass, leaf area, SPAD value, and stem thickness of flowering Chinese cabbage, promoting early seedling growth. During the mature stage, T3 treatment had the most significant effect on increasing yield. In trials conducted in Guangzhou and Foshan, T3 treatment increased yield by an average of 38.1% compared to T1 treatment and by 18.6% compared to T2 treatment. After applying N-Mg synergistic fertilizers (T3, T4), the N and Mg content of flowering Chinese cabbage significantly increased, while the phosphorus and potassium content decreased compared with T1 and T2. In addition, the application of N-Mg synergistic fertilizer (T3, T4) significantly improved the quality of flowering Chinese cabbage. Compared with the T2 treatment, the T3 treatment increased the soluble sugar, soluble protein, and vitamin C content by 17.7%, 21.4%, and 28.5%, respectively, on average. Compared with the T4 treatment, the T3 treatment increased the soluble sugar, soluble protein, and vitamin C content by 9.1%, 5.5%, and 8.1%, respectively, on average. Overall, partially replacing compound fertilizer with Mg-containing N fertilizer can effectively promote the growth of flowering Chinese cabbage seedlings, significantly increase yield, markedly improve quality, and enhance nutrient absorption and utilization efficiency. Among which, replacing 50% of farmers' customary compound fertilizer yields the best results. Thus, in flowering Chinese cabbage production, replacing part of the compound fertilizer with Mg-containing N fertilizer can reduce N fertilizer input, improve N fertilizer utilization efficiency, alleviate Mg deficiency, and enhance quality, ultimately achieving the goal of high-yield, high-quality, and green vegetable production.

Key words: N and Mg synergism, Mg-containing N fertilizer, flowering Chinese cabbage, yield, nutrient uptake, quality