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 (W1: 90% of substrate maximum water holding capacity (WHC), W2: 70% WHC, and W3: 50% WHC) and microbial fertilizer application levels (F1: 3.75 t·ha⁻¹, F2: 3.00 t·ha⁻¹, F3: 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 W2F2 treatment reached the highest, which was 88.75% higher than that of the control (CK), respectively. WUE reached the highest under W3F2 treatment, which was 78.27% higher than CK.The PFP of W2F3 treatment was the highest, compared with the lowest treatment W1F1, 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 W2F1 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 W2F2 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 W2F2 treatment, increasing by 189.35% and 81.68% compared with CK, respectively. Catalase (CAT) activity was highest under W2F1 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 W2F2 and W2F1 treatments, respectively. SQI was significantly positive correlation with Chinese cabbage yield (R² =0.781), and the highest SQI (0.87) was observed under the W2F2 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 W2F2 treatment performed optimally in increasing Chinese cabbage yield, promoting substrate nutrient accumulation, enhancing enzyme activities, and improving the comprehensive quality of the substrate.
Canopy water use efficiency (WUEc) is a critical indicator for characterizing the coupling of water and carbon processes in agroecosystems. Although groundwater serves as an important water source for crops in arid districts, the response of WUEc to groundwater depth during crop growing season remains poorly understood. We examined this relationship in an irrigated maize field in the Hetao Irrigation District by combining three years (2017 −2019) of eddy covariance observations with evapotranspiration (ET) partitioning and environmental factors measurements. The results revealed that maize transpiration accounted for an average of 85.7% of ET and daily mean WUEc was 2.68 g C kg−1 H2O. WUEc was jointly influenced by meteorological conditions, canopy development, and water availability. And groundwater table depth (WTD) was significantly and negatively associated with WUEc when surface water input was relatively low. Normalized net ecosystem productivity (NEPn) and transpiration (Tn) decreased as WTD increased, with NEPn showing greater sensitivity than Tn. As a result, WUEc remained relatively stable within the observed smaller WTD range, but declined significantly as WTD increased beyond approximately 2.0 m in the late growth stages. In particular, when root-zone soil water content (SWC) remained below field capacity (0.31 m3 m−3 in this site) for several consecutive days, a sharp decline in NEPn led to a rapid decrease in WUEc. This study demonstrates a stage-dependent response of WUEc to WTD, and highlights the importance of considering both groundwater depth and SWC in arid irrigation districts particularly in the late growing season to sustain WUEc and agricultural water productivity.
