The increasing amount of agricultural applications of controlled-release urea (CRU) and fulvic acids (FA) demands a better understanding of FA’s effects on microbially mediated nitrogen (N) nutrient cycling. Herein, a 0–60 day laboratory experiment and a consecutive pot experiment (2016–2018) were carried out to reveal the effects of using CRU on soil microbial N-cycling processes and soil fertility, with and without the application of FA. Compared to the CRU treatment, the CRU+FA treatment boosted wheat yield by 22.1%. To reveal the mechanism of CRU+FA affecting the soil fertility, soil nutrient supply and microbial community were assessed and contrasted in this research. From 0–60 days, compared with the CRU treatment, leaching NO₃⁻-N content of CRU+FA was dramatically decreased by 12.7–84.2% in the 20 cm depth of soil column. Different fertilizers and the day of fertilization both have an impact on the soil microbiota. The most dominant bacterial phyla Actinobacteria and Proteobacteria were increased with CRU+FA treatment during 0–60 days. Network analysis revealed that microbial co-occurrence grew more intensive during the CRU+FA treatment, and the environmental change enhanced the microbial community. The CRU+FA treatment, in particular, significantly decreased the relative abundance of Sphingomonas, Lysobacter and Nitrospira associated with nitrification reactions, Nocardioides and Gaiella related to denitrification reactions. Meanwhile, the CRU+FA treatment grew the relative abundance of Ensifer, Blastococcus, and Pseudolabrys that function in N fixation, and then could reduce NH₄⁺-N and NO₃⁻-N leaching and improve the soil nutrient supply. In conclusion, the synergistic effects of slow nutrition release of CRU and growth promoting of FA could improve the soil microbial community of N cycle, reduce the loss of nutrients, and increase the wheat yield.

Introduction: Nitrogen (N) loss via surface runoff is a critical issue in sloping farmland, contributing to non-point source pollution and limiting crop productivity. In peanut (Arachis hypogaea L.) production, improving nitrogen use efficiency (NUE) while minimizing environmental risks is essential for achieving sustainable agricultural development. Controlled-release compound fertilizers (CRF) may provide a promising approach to synchronizing N release with crop demand and reducing nutrient losses in runoff. This study aimed to evaluate the effects of one-time basal application of CRF on N runoff losses, NUE, and peanut yield in sloped peanut fields. Methods: A two-year field experiment was conducted in Linyi, Shandong Province, using the peanut variety ‘Huayu 25’. Treatments fertilizers included CRF and conventional compound fertilizer (CF), both with an N-P ₂ O ₅ -K ₂ O ratio of 15-15-15, applied at two application rates (800 and 560 kg hm ^-2 , representing 100% and 70% of the recommended rate) for both CRF and CF, along with a no-fertilizer control. Fertilizer release characteristics, peanut biomass and N uptake, and surface runoff nitrate (NO ₃ ⁻ –N) and ammonium nitrogen (NH ₄ ⁺ –N) concentrations and peanut yield were assessed. Results: Compared with 100%CF treatment in 2022 and 2023, 100%CRF treatment significantly reduced NO ₃ ⁻ –N and NH ₄ ⁺ –N concentrations in runoff by 21.6%–38.1% and 7.7%–63.6%, respectively, while increasing dry matter accumulation by 10.9%–12.2%, N uptake by 5.9%–6.0%, and NUE by 39.9%–40.5%. Kernel yields of 100%CRF were 6.3%–13.8% higher than those under 100%CF. Notably, the 70% CRF treatment still outperformed the 100%CF treatment in terms of yield, with increases by 3.5%–7.1% across the two years. The results highlight the potential of CRF to improve NUE and sustain or even enhance yield under reduced N inputs, offering a viable strategy for environmentally responsible and productivity-enhancing fertilization in sloping agroecosystems. Discussion: The findings indicate that CRF can simultaneously improve crop productivity and mitigate environmental pollution risks in sloping agroecosystems. Reduced-rate CRF application has strong potential as a sustainable fertilization strategy for peanut production, contributing to efficient nutrient management and environmentally responsible agriculture.

Cadmium (Cd) and arsenic (As) co-contamination in paddy soils poses a major challenge for rice safety. Humic substances have the potential to regulate the mobility of these metal(loid)s, yet the distinct effects of different humic substances on Cd/As concentrations, distribution in rice and dietary health risks remain unclear. Hence, a pot experiment was conducted using a historically mining-impacted Cd/As co-contaminated paddy soil to compare the effects of two commercial amendments, fulvic acid (FA) and humic acid (HA), under carbon-equivalent application rates on Cd/As extractability and concentration-based distribution across the soil–root surface-grain continuum and the associated potential dietary risk. Each treatment consisted of three replicate pots, with each pot serving as the experimental unit (39 pots in total). The results showed that adding FA and HA decreased CaCl₂-Cd by 24.64–67.63%, while increasing the KH₂PO₄-As by 15.83–44.55%. This reduction in Cd extractability was accompanied by an increase in Fe/Mn oxide-bound Cd. Moreover, the increase in extractable As was associated with increases in soluble and Al-bound As, and a decrease in Fe-bound As. These changes were associated with increased organic carbon, lower Eh, and changes in Fe oxide fractions. The FA and HA additions also decreased grain Cd concentrations to 0.05–0.30 mg kg⁻¹, corresponding to reductions of 30.95–87.68%. However, grain As concentrations showed amendment- and dose-dependent responses, ranging from 0.48 to 0.62 mg kg⁻¹ and decreasing by 10.50–12.47% at higher FA rates but increasing by 12.09–14.21% under some HA treatments. These contrasting grain As responses were associated with changes in plaque-associated As and concentration-based transfer factors, suggesting altered As distribution among rice tissues. Correlation and Random Forest analyses indicated that DOC, metals in iron plaque, and pH were the variables most strongly associated with grain Cd/As variation in this study. Because inorganic As was not determined, total grain As was used as a conservative surrogate for inorganic As in the screening-level health risk assessment. Under this assumption, HQ-As was the dominant contributor to HI, and all HI values remained greater than 1, despite reductions in HQ-Cd. Overall, both amendments reduced grain Cd concentration, but their combined Cd/As responses varied across application rates. Higher FA rates reduced both grain Cd and grain As, whereas intermediate HA rates increased grain As despite reductions in grain Cd. These findings demonstrate amendment- and dose-dependent Cd/As trade-offs across the soil–rice continuum and highlight that increased soil As extractability does not necessarily translate into increased grain As concentration.