The Effect of Nitrogen Fertilizer Reduction and Application of Microbial Agents on Spinach Growth and Quality

In order to explore the effect of increasing microbial agents on the growth and quality of spinach under the condition of reducing nitrogen fertilizer application. In the pot experiment, six nitrogen fertilizer gradients were set up in the soil, N1 was a constant fertilization treatment（225 kg·hm⁻², equivalent to 103.5 kg·hm⁻² pure nitrogen）. Compared with N1 constant fertilization treatment, N2～N5 reduced nitrogen by 20%, 25%, 30% and 35%, respectively. N6 was 100% nitrogen reduction treatment. Under each nitrogen fertilizer level, water control（CK）, SDB5 microbial agent and SDB9 microbial agent were set up, which were combined into 18 treatments. The effects of different treatments on the growth index and nutritional quality of spinach were investigated. The results showed that the leaf number, plant height and aboveground fresh weight of spinach increased significantly with the application of SDB5 and SDB9 microbial agents at N4 level. Compared with N4-CK, the number of leaves of N4-SDB5 and N4-SDB9 increased by 30%, the plant height of N4-SDB9 increased by 18.2%, and the aboveground fresh weight of N4-SDB5 increased by 57.5%, reaching 6.3 g. The improvement effect of SDB9 microbial agent on nutritional indexes at N3 level was better than that of other treatments, while SDB5 microbial agent had better effect on reducing nitrate content in leaves at N4 level. Compared with N3-CK spinach leaves, the soluble protein content of N3-SDB9 spinach leaves increased by 24.2%, the nitrate content decreased by 17.5%, and the oxalic acid content decreased by 48.2%, the difference was significant. There was no significant difference in soluble sugar and vitamin C content. The nitrate content of N4-SDB5 was significantly lower than that of N4-CK by 46.9%. In summary, reducing nitrogen by 25% ～ 30% and increasing SDB5 and SDB9 microbial agents can promote the growth of spinach to a certain extent and improve the nutritional quality.