Fertilizer sources may have variable effects on soil aggregation, aggregated-associated C and N, and wheat yield. A 34-year field experiment was performed to evaluate the influences of chemical and organic fertilization on soil aggregates and associated carbon and nitrogen under winter wheat in a Cumulic Haplustoll of the Loess Plateau, China. Treatments included unfertilized control (CK), inorganic N fertilizer (NF), inorganic P fertilizer (PF), inorganic N and P fertilizer (NP), organic manure (M), inorganic N fertilizer plus manure (NM), inorganic P fertilizer plus manure (PM), and inorganic N plus P fertilizers plus manure (NPM). Compared to CK, long-term fertilization significantly increased the proportion of soil macro-aggregates, mean weight diameter (MWD), and geometric mean diameter (GMD), but decreased the proportion of micro-aggregates and fractal dimension, especially fertilizer plus manure. Compared to CK, manure treatments (M, NM, PM, and NPM) had a better improvement on soil organic carbon (SOC), soil total nitrogen (STN), particle organic C, and microbial biomass C in all aggregates than the fertilizer alone. The SOC in different aggregates increased with the increased aggregate size, which was because the larger aggregates formed by the binding of the smaller aggregates and organic matter. PON increased in NM and NPM, and MBN was more sensitive to N fertilizer. The C/N ratio in bulk soil and aggregates decreased with fertilization, especially in fertilizer with manure and in macro-aggregates. The improved soil structure was related to the increased SOC and STN, which was proved by the positive correlations among SOC and STN with macro-aggregates and MWD. A correlation analysis also showed that the contribution rate of SOC and STN in macro-aggregates was positively associated with the macro-aggregate and stability. Therefore, the sequestration of C and N in soil was related to aggregate size and was mainly affected by larger aggregates. The results demonstrated that fertilizer with manure improved the soil structure and fertility better than fertilizer alone, thus increasing crop yield.

Facility agriculture is essential for modernizing the production of horticultural plants, while long-standing over-fertilization and improper tillage in some vegetable facilities in northern China have resulted in reduced soil quality, increased greenhouse gas (GHG) emissions, and diminished vegetable yields and quality. This study systematically analyzed the deteriorating health of typical cucumber facility soils in Hebei Province, China, induced by long-term over-fertilization. Based on field surveys, we explored dynamic changes in soil physicochemical properties across different durations of over-fertilization. Subsequently, a series of field trials were conducted to assess whether reducing nitrogen application, either alone or when combined with microbial agents, could ameliorate soil properties, reduce greenhouse gas emissions, and enhance cucumber productivity. The initial field assessment revealed severe topsoil salt and nutrient accumulation, with water-soluble salt content in 5-year-old greenhouses from Yongqing soaring to 3.82 g·kg⁻¹, nearly eight times the level found in 1-year-old plots. Field experiments demonstrated that a 20% reduction in nitrogen application from the conventional rate of 900 kg·hm⁻² effectively mitigated salt accumulation, improved the structure of the microbial community, and maintained cucumber yield at 66,914 kg·hm⁻², an output comparable to conventional practices. More notably, integrating this 20% nitrogen reduction with an inoculation of Bacillus megaterium reduced the overall global warming potential by 26.7% and simultaneously increased cucumber yield to 72,747 kg·hm⁻². The most comprehensive strategy combined deep tillage, soybean straw incorporation, and B. megaterium application under reduced nitrogen, which boosted nitrogen use efficiency by 13.7% and achieved the highest yield among all treatments. In conclusion, our findings demonstrate that a combined approach of nitrogen reduction, microbial amendment, and straw application offers an effective strategy to restore soil health, enhance crop productivity, and mitigate environmental impacts in protective vegetable production systems.

Nitrogen (N) fertilization critically regulates the storage and availability of soil carbon (C) and N pools. However, the internal mechanism through which stratified N application affects soil organic carbon (SOC) sequestration and soil quality index (SQI) remains unclear. To investigate the effects of stratified N application on C sequestration and SQI in both topsoil and subsoil, this study established six treatments (N_0:0, N_1:0, N_4:1, N_3:2, N_2:3, N_1:4) and analyzed soil biochemical indicators. The results showed that compared to N_1:0, stratified N fertilization did not significantly improve soil C and N content in the 0–20 cm layer. In contrast, the N_2:3 and N_1:4 treatments even led to a significant reduction in soil C and N pools in the topsoil. In the 20–40 cm, compared to N_1:0, stratified N fertilization increased SOC, TN, labile C fractions, N fractions (particulate organic N and microbial biomass N), enzyme activity and C pool management index (CPMI), increasing by 0.52–7.94%, 2.05–8.42%, 4.77–42.59%, 14.46–56.01%, 6.34–45.82%, and 31.26–51.93%, respectively. In 0–20 cm, compared to N_0:0, N application increased SQI by 24.84–45.77%, and N_2:3 and N_1:4 treatments were lower SQI than N_1:0. Furthermore, N_2:3, N_3:2, and N_1:4 treatments in 20–40 cm were higher than other treatments. N fertilizer application drives the synergistic changes in C and N fractions by regulating enzyme activity and stoichiometric ratio, thus affecting CPMI and SQI. Thus, the 3:2 stratified N fertilization (0–20 cm:20–40 cm) method achieves synergistic dual-layer enhancement-maintaining surface C and N pools while boosting subsoil C sequestration and quality-through enzyme-mediated precision regulation of C/N stoichiometry. The study provides a scientific foundation for integrated C emission reduction and cropland quality enhancement in the North China.