Exploring the temporal evolution dynamics of different soil organic nitrogen (N) components under different water–N management practices is a useful approach to accurately assessing N supply and soil fertility. This information can provide a scientific basis for precise water and N management methods for greenhouse vegetable production. The objective of this study was to investigate the effects of optimized irrigation and nitrogen management on the dynamics of soil organic nitrogen fractions, soil properties, and crop growth. This research was conducted from 2017 to 2023 in a greenhouse vegetable field in North China. Four treatments were applied: (1) high chemical N application with furrow irrigation (farmers’ practice, FP); (2) no chemical N application with drip irrigation (DN0); (3) 50% N of FP with drip irrigation (DN1); and (4) 75% N of FP with drip irrigation (DN2). The volume in drip irrigation is 70% of that in furrow irrigation. The results showed that in 2023 (after seven years of field trials), compared with FP, the soil organic carbon (SOC), total N, and water use efficiency of the DN1 and DN2 treatments increased by 15.9%, 11.4%, and 11.3% and 7.7%, 47.2% and 44.6%, respectively. However, there was no significant difference in the total crop yield except in the DN0 treatment. Soil organic N was mostly in the form of acid-hydrolyzed N (AHN). After seven years of optimized irrigation and N management, the DN1 treatment significantly increased the content of ammonium N (AN) and amino sugar N (ASN) in AHN compared with the FP treatment. The results of further analysis demonstrated that SOC was the main factor in regulating AHN and non-hydrolyzable N (NHN), while the main regulatory factors for amino acid N (AAN) and ASN in the AHN component were dry biomass and water use efficiency, respectively. From a time scale perspective, optimization of the water and N scheduling, especially in DN1 (reducing the total irrigation volume by 30% and the amount of N applied by 50%), is crucial for the sustainable improvement of soil fertility and the maintenance of vegetable production.

Calcium (Ca) is one of the most important elements determining vegetable yield, but the driving factors that regulate microbial community structure, microbial network system stability, and metabolic pathways along the soil Ca gradient remain unclear. In this work, the relationship between soil physicochemical properties and bacterial and fungal communities was investigated under distinct Ca gradients in well-established Chinese cabbage fields located in Shijiazhuang, Hebei Province, China, with sites named Group 1 (G1), Group 2 (G2), and Group 3 (G3) from lowest to highest along the soil Ca gradient. This study demonstrated that Ca exerts dual effects by modulating pH, electrical conductivity (EC), and soil organic carbon (SOC) dynamics, enhancing bacterial diversity while reinforcing fungal network stability through distinct metabolic adaptations. Bacterial networks showed reduced stability despite increased diversity, perhaps linked to the downregulation of ATP-binding cassette (ABC) transporters. Notably, Fe-Mn oxides counteracted Ca influences through selective nutrient adsorption, creating antagonistic selection pressures. Under calcium stress, both Ca and total P (TP) emerge as key drivers of microbial community restructuring, with fungal networks exhibiting significantly greater stability compared to their bacterial counterparts. This study bridges the knowledge gap in the driving mechanisms of microbial communities under soil Ca stress and provides a theoretical basis for improving vegetable yields, with implications for soil management in Ca-rich ecosystems.