Conventional fertilization in the greenhouses of North China used excessive amounts of chemical and organic fertilizer, resulting in soil degradation and severe agricultural non-point source pollution. A nine-year study was conducted on a loamy clay soil in Shijiazhuang, Hebei province, to investigate the effects of reduced-fertilizer input regimes on soil property, bacterial diversity, nitrogen (N) cycling and their interactions. There were four treatments, including high organic + chemical fertilizer application rate and three reduced-fertilizer treatments with swine manure, maize straw or no substitution of 50% chemical N. Treatments with reduced-fertilizer input prevented soil salinization and acidification as in local conventional fertilization after being treated for nine years. In comparison to chemical fertilizer only, swine manure or maize straw substitution maintained higher nutrient availability and soil organic C contents. Fertilizer input reduction significantly increased bacterial richness and shifted bacterial community after nine years, with decisive factors of EC, Olsen P and C/N ratio of applied fertilizer. Soil chemical characteristics (EC, pH and nutrients), aggregation and C/N ratio of applied fertilizer selected certain bacterial groups, as well as N-cycling functions. Reduced-fertilizer input decreased the potential nitrification and denitrification functioning of bacterial community, but only in organic substitution treatments. The results of this study suggested that fertilizer input reduction combined with organic C input has potential in reducing non-point source pollution and increasing N-use efficiency in greenhouse vegetable production in North China.

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.

As the largest organic carbon input to agroecosystems, crop straw can solve the problem of soil quality degradation in greenhouse vegetable fields, harmonize the balance between soil nutrients and energy, and improve soil quality to maintain the sustainable production of greenhouse vegetables. However, the microbial mechanism of the straw decomposition process under different temperatures and fertilization treatments in greenhouse vegetable soils has not been clarified. Soil samples were used to investigate the biology of straw decomposition in the soil at three incubation temperatures (15, 25, and 35 °C) through a soil incubation experiment (60 d) under different fertilization treatments. Fertilization treatments for this long-term field experiment included chemical fertilizer (CF), substitution of half of the chemical N fertilizer with manure (CM), straw (CS), or combined manure and straw (CMS). The results showed that soil hydrolase activities tended to decrease with increasing temperature during straw decomposition. Compared with the CF, organic substitutions (CM, CMS, and CS) increased soil β-glucosidase, β-cellobiosidase, N-acetyl-glucosaminidase, and β-xylosidase activities during straw decomposition. Soil CO₂ emission rates were the highest at each incubation temperature on the first day, rapidly declining at 25 °C and 35 °C and slowly declining at 15 °C. The soil CO₂ cumulative emissions tended to increase with increasing temperature under different fertilization treatments. PCA showed that the responses of soil enzyme activities to temperature at 7, 15, and 30 d of straw decomposition were stronger than those of fertilization. In summary, both fertilization treatment and incubation temperature could influence soil CO₂ emissions by affecting soil physicochemical properties and enzyme activities during straw decomposition, whereas incubation temperature had a stronger effect on straw decomposition than fertilization, as indicated by PLS-PM and three-way ANOVA. Considering the influence for fertilization on the straw decomposition process at different incubation temperatures, the straw applications (CMS and CS) were more suitable to temperature changes.

Microbial necromass C (MNC) represents a substantial pool of soil organic C (SOC), but its long-term response to organic N substitution remains poorly resolved in open-field vegetable soils. We examined endpoint soils from a 13-year equal-N field trial on a calcareous cinnamon soil in North China. The four regimes were mineral N alone (N₁₀₀), 25% N substitution with manure (N₇₅M₂₅), 25% with straw (N₇₅S₂₅), and 50% with equal manure and straw contributions (N₅₀M₂₅S₂₅). Fungal necromass C (FNC), bacterial necromass C (BNC), and total MNC were quantified and related to soil nutrient stoichiometry, extracellular enzyme stoichiometry, and PLFA-based microbial community structure. All organic substitution treatments increased FNC, BNC, and MNC relative to N₁₀₀. N₅₀M₂₅S₂₅ showed the highest FNC, BNC, and total MNC contents, which were 100.28%, 88.68%, and 97.68% higher than those under N₁₀₀, respectively. FNC comprised 77.32–80.19% of total MNC. N₇₅S₂₅ had the highest FNC/BNC ratio and increased FNC/SOC and MNC/SOC by 25.26% and 21.25%, respectively. Organic substitution also increased SOC and total N, altered nutrient and enzyme stoichiometry, and raised the fungi-to-bacteria and Gram-positive-to-Gram-negative bacterial ratios. Random Forest ranked EEC:EEN highest for FNC and total MNC, whereas soil N:P ranked highest for BNC. PLS-PM indicated that MNC variation was most strongly associated with microbial community structure within a network linked to soil nutrient and enzyme stoichiometry. Overall, combined manure–straw substitution was associated with the highest bulk-soil MNC content, together with coordinated shifts in nutrient stoichiometry, enzyme allocation, and microbial community structure, highlighting its potential to enhance microbial-derived C accumulation in open-field vegetable soils.

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.