Irrigation and microbial fertilizer synergistically improved the substrate health status and water and fertilizer use efficiency of facility Chinese cabbage

Improper irrigation and fertilization in facility substrate cultivation can lead to substrate degradation and inefficient use of water and fertilizer resources, thereby constraining high-quality and sustainable production of vegetables. This study investigated Chinese cabbage grown in facility substrate cultivation, with three irrigation levels (W 1 : 90% of substrate maximum water holding capacity (WHC), W 2 : 70% WHC, and W 3 : 50% WHC) and microbial fertilizer application levels (F 1 : 3.75 t·ha⁻¹, F 2 : 3.00 t·ha⁻¹, F 3 : 2.25 t·ha⁻¹), to evaluate the effects of different water–fertilizer combinations on Chinese cabbage yield, water use efficiency (WUE), partial factor productivity of fertilizer (PFP), substrate physicochemical properties, enzyme activities, and microbial community structure. Additionally, a substrate quality index (SQI) was constructed based on multiple indicators to evaluate the effects of synergistic irrigation and fertilizer management on substrate health. The results showed that both irrigation and microbial fertilizer application significantly affected Chinese cabbage yield, WUE and PFP. Among them, the yield of Chinese cabbage under W 2 F 2 treatment reached the highest, which was 88.75% higher than that of the control (CK), respectively. WUE reached the highest under W 3 F 2 treatment, which was 78.27% higher than CK.The PFP of W 2 F 3 treatment was the highest, compared with the lowest treatment W 1 F 1 , it increased by 87.28% and 95.51% respectively. Irrigation and microbial fertilizer application significantly altered substrate nutrient contents and enzyme activities. Specifically, the substrate organic matter (SOM) and ammonium nitrogen (NH₄⁺-N) contents were highest under W 2 F 1 treatment, increasing by 56.62% and 72.65% on average compared with CK, respectively. Available potassium (AK) and Available phosphorus (AP) contents initially increased and then decreased with increasing irrigation amount and microbial fertilizer application rates, reaching their maximum values under W 2 F 2 treatment, which were 56.11% and 63.32% higher on average than those under CK, respectively. Enzyme activity analysis showed that the activities of urease (UR) and phosphatase (PHO) were highest under W 2 F 2 treatment, increasing by 189.35% and 81.68% compared with CK, respectively. Catalase (CAT) activity was highest under W 2 F 1 treatment, increasing by 32.28% on average compared with CK. Microbial community analysis revealed that irrigation and microbial fertilizer application altered the composition of substrate bacterial and fungal communities. Among the dominant phyla, the relative abundances of Proteobacteria and Ascomycota were highest under the W 2 F 2 and W 2 F 1 treatments, respectively. SQI was significantly positive correlation with Chinese cabbage yield ( R ² =0.781), and the highest SQI (0.87) was observed under the W 2 F 2 treatment, while was significantly higher than that under CK treatments (0.085). Path analysis further revealed that AK and PHO were the primary factors affecting SQI. Overall, the W 2 F 2 treatment performed optimally in increasing Chinese cabbage yield, promoting substrate nutrient accumulation, enhancing enzyme activities, and improving the comprehensive quality of the substrate.