Ammonia oxidizing archaea (AOA) and bacteria (AOB) mediate a crucial step in nitrogen (N) metabolism. The effect of N fertilizer rates on AOA and AOB communities is less studied in the wheat-fallow system from semi-arid areas. Based on a 17-year wheat field experiment, we explored the effect of five N fertilizer rates (0, 52.5, 105, 157.5, and 210 kg ha⁻¹ yr⁻¹) on the AOA and AOB community composition. This study showed that the grain yield of wheat reached the maximum at 105 kg N ha⁻¹ (49% higher than control), and no further significant increase was observed at higher N rates. With the increase of N, AOA abundance decreased in a regular trend from 4.88 × 10⁷ to 1.05 × 10⁷ copies g⁻¹ dry soil, while AOB abundance increased from 3.63 × 10⁷ up to a maximum of 8.24 × 10⁷ copies g⁻¹ dry soil with the N105 treatment (105 kg N ha⁻¹ yr⁻¹). Application rates of N fertilizer had a more significant impact on the AOB diversity than on AOA diversity, and the highest AOB diversity was found under the N105 treatment in this weak alkaline soil. The predominant phyla of AOA and AOB were Thaumarchaeota and Proteobacteria, respectively, and higher N treatment (N210) resulted in a significant decrease in the relative abundance of genus Nitrosospira. In addition, AOA and AOB communities were significantly associated with grain yield of wheat, soil potential nitrification activity (PNA), and some soil physicochemical parameters such as pH, NH₄-N, and NO₃-N. Among them, soil moisture was the most influential edaphic factor for structuring the AOA community and NH₄-N for the AOB community. Overall, 105 kg N ha⁻¹ yr⁻¹ was optimum for the AOB community and wheat yield in the semi-arid area.

Bacterial diversity and its functions are essential to soil health. N fertilization changes bacterial communities and interferes with the soil biogeochemical N cycle. In this study, bacterial community and soil physicochemical properties were studied in 2018 after applying N fertilizers (0, 52.5, 105, 157.5, and 210 kg N ha⁻¹) for a long (2003–2018) and a short (2003–2004) duration in a wheat field on the Loess Plateau of China. Soil bacteria were determined using 16S rRNA Illumina-MiSeq^®, and the prediction function was analyzed through PICRUSt. The study showed that N fertilizer significantly changed the diversity and abundance of bacterial communities. The phyla Proteobacteria, Actinobacteria, Acidobacteria, and Chloroflexi were most abundant, accounting for 74–80% of the bacterial community abundance. The optimum rates of N fertilizer application (N105) maintain soil health by promoting soil microbial diversity and abundance. The bacterial population abundance was higher after short-term N application than after N application for a long duration and lowest with the high N-fertilizer treatment (N210). High N enrichment led to more heterotrophic N-fixing microorganisms (Alphaproteobacteria), in which metabolism and genetic information processing dominated, while cellular processes, genetic information processing, metabolism, and organismal systems were the main functional categories under low N. The phyla Gemmatimonadetes, Actinobacteria, Bacteroidetes, and Chloroflexi were the key bacteria in the co-occurrence network. The genus Saccharimonadales of the superphylum Patescibacteria has a more significant impact under low N treatment. Long-term N fertilization affected the soil pH, NO₃-N, and other physicochemical properties, and soil NO₃-N was the highest indicator, contributing 81% of the bacterial community function under different N fertilizer treatments.

To investigate the effects and mechanism of prolonged inorganic nitrogen (N) fertilization on the N-use efficiency of spring wheat (Triticum aestivum L.), a long-term study initiated in 2003 was conducted. The study analyzed how N fertilization affects dry matter translocation, N translocation, soil NO₃-N, and N-use efficiency. Five different N-fertilizer rate treatments were tested: N0, N52.5, N105, N157.5, and N210, corresponding to annual N fertilizer doses of 0, 52.5, 105.0, 157.5, and 210.0 kg N ha⁻¹, respectively. Results showed that increasing N-fertilizer rates significantly enhanced the two-year average dry matter accumulation amount (DMA) at maturity by 22.97–56.25% and pre-flowering crop growth rate (CGR) by 17.11–92.85%, with no significant increase beyond 105 kg N ha⁻¹. However, no significant correlation was observed between the dry matter translocation efficiency (DTE) and wheat grain yield. Both insufficient and excessive N applications resulted in an imbalanced N distribution favoring vegetative growth over reproductive growth, thus negatively impacting N-use efficiency. At maturity, the N-fertilized treatments significantly increased the two-year average N accumulation amount (NAA) by 52.04–129.98%, with no further increase beyond 105 kg N ha⁻¹. N fertilization also improved the two-year average N translocation efficiency (NTE) by 56.89–63.80% and the N contribution proportion (NCP) of wheat vegetative organs by 27.79–57.83%, peaking in the lower-N treatment (N52.5). However, high-N treatment (N210) led to an increase in NO₃-N accumulation in the 0–100 cm soil layer, with an increase of 26.27% in 2018 and 122.44% in 2019. This higher soil NO₃-N accumulation in the 0–100 cm layer decreased NHI, NUE, NAE, NPFP, and NMB. Additionally, N fertilization significantly reduced the two-year average N harvest index (NHI) by 9.89–12.85% and N utilization efficiency (NUE) by 11.14–20.79%, both decreasing with higher N application rates. The NAA followed the trend of anthesis > maturity > jointing. At the 105 kg N ha⁻¹ rate, the highest N agronomic efficiency (NAE) (9.31 kg kg⁻¹), N recovery efficiency (NRE) (38.32%), and N marginal benefit (NMB) (10.67 kg kg⁻¹) were observed. Higher dry matter translocation amount (DTA) and N translocation amount (NTA) reduced NHI and NUE, whereas higher NTE improved NHI, NUE, and N partial factor productivity (NPFP). Overall, N fertilization enhanced N-use efficiency in spring wheat by improving N translocation rather than dry matter translocation.

One of the main factors influencing wheat productivity is nitrogen (N) management. This study examined the impact of varying N-fertilizer rates on spring wheat yield and N use efficiency by adjusting the “source-sink” relationship between assimilates and N accumulation and transport. The objective was to identify the optimal N rate for the region. The field experiment included five N-fertilizer rates: 0 kg ha⁻¹ (N1), 52.5 kg ha⁻¹ (N2), 105.0 kg ha⁻¹ (N3), 157.5 kg ha⁻¹ (N4), and 210.0 kg ha⁻¹ (N5). Results indicated that the yield response was not proportional to N-fertilizer rates, with maximum biomass (6029 kg ha⁻¹) and grain yield (2625 kg ha⁻¹) achieved under N3. N fertilization primarily increased yield by regulating pre-anthesis translocation of assimilate and N. Assimilate translocation peaked at 105 kg N ha⁻¹, increasing by 8.5–133.7% compared to other treatments. With increasing N input, N absorption efficiency and N partial factor productivity declined. The highest N agronomic use efficiency was observed under N3, which was 19.5–176.34% higher than other treatments. Overall, moderate N input (≈105 kg ha⁻¹) optimizes yield and N-use efficiency, offering guidance for sustainable N management in dryland spring wheat production.

Soil organic carbon (SOC) sequestration is vital for sustaining soil health, maintaining agricultural productivity, and combating land degradation in drylands. In these fragile regions, water scarcity, calcareous chemistry, and soil erosion create distinct challenges that traditional climate–substrate–disturbance frameworks fail to fully capture. Although numerous reviews have examined conservation management, they typically evaluate physical, biochemical, and microbial mechanisms in isolation, leaving their cross-regulations largely unresolved. To bridge this gap, we propose a coupled framework that merges physical aggregate protection with biochemical nutrient limitation. By linking ecoenzymatic stoichiometry to the soil aggregate hierarchy, our approach tracks metabolic signals alongside micro-structural changes. Drawing on evidence from the Loess Plateau and comparable semi-arid environments, we suggest that conservation practices stabilize SOC mainly by preserving pre-existing protected carbon rather than by forming new protective structures. Furthermore, the evidence suggests that this physical protection capacity is finite and texture-dependent, and, in the studies reviewed, physical and biochemical indicators together explain a large share of the variation in carbon mineralization. This framework offers an explanation for why four core agronomic practices (no-till duration, straw return rates, subsoiling frequency, and crop rotation combination) often show diminishing or context-dependent returns rather than linear increases, with diminishing responses consistent with capacity saturation. Finally, given the current scarcity of empirical data on tillage-driven nutrient limitations across aggregate fractions, we outline how integrating microbial–mineral carbon pump theory with long-term experimental networks could extend this framework for optimizing dryland agriculture.

Introduction: Carbon sequestration and emission reduction in farmland ecosystems are central to sustainable agricultural development. This study evaluated whether organic-inorganic fertilization could coordinate soil carbon accumulation, respiratory carbon losses, crop productivity, and bacterial community structure in a semiarid dryland maize system. Methods: Using a long-term fixed-site field experiment established in 2012, we compared five fertilization regimes during 2024 and 2025: no fertilization (NA), chemical fertilizer alone (CF), combined organic and chemical fertilization (SC), organic fertilizer alone (SM), and maize straw alone (MS). We measured maize productivity, soil total carbon and nitrogen, soil organic carbon and labile carbon fractions, soil CO ₂ emissions, and bacterial community composition. Results: Fertilization increased grain yield and soil carbon and nitrogen pools, although its effects on the growing-season carbon budget differed among treatments. SC produced the highest grain yield, improved carbon emission efficiency, and maintained positive growing-season net ecosystem productivity within the accounting framework used in this study. Compared with NA, SC and CF increased grain yield by 235.4% and 195.3%, respectively. Although SM and MS increased soil carbon and nitrogen pools, neither improved the growing-season balance between crop production and respiratory carbon losses. MS produced the highest total carbon emissions and the most negative net ecosystem productivity. Fertilization primarily altered bacterial community composition through treatment-specific shifts in dominant taxa. SC and CF favored Gemmatimonadota-related groups, whereas MS enriched copiotrophic and substrate-responsive groups, including Proteobacteria and Bacteroidota. Discussion: These findings indicate that integrated organic-inorganic fertilization may be more effective than high organic-carbon inputs alone for coordinating maize productivity, soil carbon accumulation, and growing-season carbon performance in semiarid dryland maize systems.