Abiotic clay mineral fixation and release of ammonium (NH₄⁺) is a key process regulating nitrogen (N) retention and supply in Northeast China's black soil region. However, the long-term effects of chemical fertilizer, manure, and nitrification inhibitors on NH₄⁺ fixation capacity, as well as their relationship with organic matter and yield,remain unclear. This study evaluated 42-year fertilization practices (CK, NPK, NPKM1 with low-level manure, NPKM2 with high-level manure) and the nitrification inhibitor DMPP on fixed NH₄⁺ and maximum fixation capacity in thin-layer black soil (0-100 cm). Results showed that fixed NH₄⁺ ranged from 134.9–225.4 mg kg⁻¹ after 42 years. All fertilization treatments increased fixed NH₄⁺ in the 0-20 cm layer, but only NPKM2 increased it in 20-100 cm depth. Fixed NH₄⁺ accounted for 9.9-32.9% of total N across the 100 cm profile. Maximum fixation capacity (511.0-810.4 mg kg⁻¹) was much higher than actual fixed NH₄⁺, indicating high fixation potential. Manure application (NPKM1 and NPKM2) significantly increased soil organic matter (SOM) in 0-20 cm and promoted maize yield. However, although NPKM2 had higher SOM than NPKM1, yields did not differ between the two treatments. DMPP increased fixed NH₄⁺ by 6.6-15.5% in the early stage (3-7 days) and consistently enhanced fertilizer-derived fixed NH₄⁺, though this effect was weaker under NPKM treatments. In conclusion, integrated fertilizer-manure application (especially with nitrification inhibitors) can increase the fixed NH₄⁺ pool, thereby enhancing N retention and supply, SOM, and crop yield in Northeast China's thin-layer black soil.

The substitution of mineral fertilizer with organic fertilizer can help improve soil fertility and reduce environmental emissions, but the extent to which organic fertilizer should replace chemical nitrogen (N) fertilizer with respect to phosphorus (P) risk management remains unclear. In this study, we aimed to investigate the effects of organic fertilizer substitution on soil P and crop yield through a five-year field experiment. Four treatments were arranged, including chemical fertilizer N but no P (C1), chemical fertilizer (C2), 25 % organic fertilizer substitution based on N addition (M1), 50 % organic fertilizer substitution (M2) and 100 % organic fertilizer substitution (M3). The results indicated that the overall yield of the three organic fertilizer substitution treatments was lower than that of the C2 treatment, but only M3 and C2 showed significant differences. Compared with the C1 treatment, the C2, M1, and M2 treatments did not increase TP, Olsen-P or labile-P, while their contents were high in the upper soil of M3. Path analysis between different P fractions and Olsen-P revealed that resin-P, NaHCO3-Pi, and NaOH-Pi had the greatest direct effect on Olsen-P, but NaHCO3-Po and NaOH-Po might transform into OlsenP through NaHCO3-Pi and NaOH-Pi. Our results suggested that partial substitution of chemical fertilizers not only ensured yield but also did not increase the risk of P leaching, making it more feasible than full substitution with organic fertilizers. The substitution of organic fertilizer would lead to more conversion of organic P into inorganic P to maintain the soil Olsen-P level. These results contribute to a better understanding of the influence of the substitution of organic fertilizer on the P pool and thus clarify the appropriate proportion of substitution.

Here, we conducted a seven-year field experiment in black soils of Northeast China to evaluate the effects of carbon (C) management, that is, control, straw return (SD), straw-biochar (BC), and a combined amendment (SDBC), with three fertilization levels (N0: unfertilized control, N60: 60% of conventional rates, N100: conventional rates) on soil microbiomes, metagenomics, and metabolomics. Results showed that BC significantly elevated soil total C (+15%), total N (+10%), and NH 4 + $$ {\mathrm{NH}}_4^{+} $$ (+63%) relative to controls. Microbial community analyses revealed that SD increased prokaryotic richness but reduced protist diversity, whereas BC and SDBC suppressed fungal diversity. Integrated metagenomic and metabolomic profiling uncovered microbial functional adaptations to rich-C conditions under BC and SDBC, characterized by downregulated C metabolism-related genes and concurrent accumulation of lipid-associated metabolites. Crucially, BC decreased the abundance of bacterial virulence factors, contrasting with SD elevating pathogenic potentials. Among three fertilization levels, the reduced rates of N60 optimized microbial network complexity and minimized pathogen invasion risks more effectively than conventional rates of N100 without compromising soil fertility. Collectively, by deciphering prokaryote-fungus-protist interactions and metagenomic-metabolite linkages, our research highlights that straw-derived biochar application and optimized fertilization offers a sustainable strategy to foster beneficial microbial associations, suppresses pathogenic potential, and enhances carbon storage.

Soil organic matter (SOM) is crucial for the productivity of greenhouse soils, yet its chemical composition over time has not been well explored, particularly under high-intensity tillage practices. This study analyzed the dynamic changes in the chemical composition of SOM based on 78 soil samples collected across different cropping years in Eastern China. The study site features a typical temperate continental monsoon climate, and the surveyed greenhouse and farmland soils are all cinnamon soils. Soils were categorized into four groups based on land use and cropping years. Fourier transform infrared (FTIR) spectroscopy was used to assess the chemical composition of SOM. High-intensity greenhouse cultivation induces significant and non-linear alterations in SOM chemical composition. The specific manifestations are the selective consumption of labile functional groups and the gradual intensification of SOM aromatization. Compared to field soils, polysaccharide-C decreased by 5.47

It is challenging by popular water-nitrogen coupled drip fertigation (CF) to control dissolved nitrogen (DN) leaching in greenhouse soils planted with cucumber-represented vegetables that often need sufficient and frequent irrigation to ensure yields. This study proposed water-nitrogen partially decoupled drip fertigation (DF) as a substitute for CF to cut DN leaching from cucumber-planted greenhouse soil without cutting water and N input. DF performance in comparison with CF in soil DN leaching control was evaluated both theoretically based on presumed criteria and experimentally in a greenhouse loam soil without and with cucumbers. DF had a good potential in reducing DN leaching under moderate water leaching (15 %-25 %) when the ratio of irrigation and the ratio of N fertilization in water-more-dissolved nitrogen-less (WM) and water-less-dissolved nitrogen-more (WL) subzone soil specially formed under DF were respectively set at 2.0-3.0 and 0.6-0.8. Experimental results showed that the reduction effect of DF was limited on water leaching (<10 %) but significant on DN leaching, especially with cucumbers. The cumulative leaching loss of DN dominated by nitrate N (>75 %) from seven leaching events during the water demand-high fruiting period under moderate water leaching (averagely around 15 %) was 41.7 % lower (p < 0.05) under DF than under CF, predominantly (78.3 %) via lowering its availability in leachate. Moreover, DF increased the cucumber yield somewhat with retention of significantly more nitrate N mainly in WL subzone soil. The presence of cucumber improved DF performance mainly by absorbing more water from WM subzone soil than from WL subzone soil to weaken lateral diffusion of water and nitrate-dominated DN between WM and WL subzone soil, lowering DN level in leachate mainly derived from WM subzone soil while enhancing its level mainly in WL subzone soil. Hence, DF may replace CF to cut N leaching without cutting irrigation in greenhouse soils cultivated with cucumber-represented vegetables needing sufficient and frequent irrigation.

Soil nitrogen (N) transformation is a critical step in grassland N cycling. Nitrogen fertilization, a widely used restoration strategy in global grasslands, alters soil N transformation. Nevertheless, the responses of soil N transformation to multiple N input levels and the driving factors remain unclear. With 15N tracing technique, we assessed the variations of gross and net N mineralization and nitrification rates across wide-ranging N fertilization levels (0, 2, 5, 10, and 20 g N m−2 yr−1) after seven years of treatment in a temperate grassland. Plant, soil and microbial traits were analyzed to explore the regulatory mechanisms of N fertilization on soil N transformations. Both soil gross N mineralization (GNM) and nitrification rates (GN) showed positive responses to increasing N fertilization levels, with consequences on net N mineralization and nitrification rates. The consistent increases of GNM were primarily driven by the soil dissolved organic N availability. The enhancement of GN was attributed to the increases in GNM-derived NH+ content and the ammonium-mediated decreases in ammonia-oxidizing archaea to bacteria ratio (AOA:AOB). The role of GNM was more predominant under higher N fertilization rate. Mineralization-derived substrates quantity and ammonia-oxidizing community structure co-driven the responses of grassland soil nitrification to N fertilization, with soil substrates being predominant under higher N fertilization. Our findings emphasize that the drivers of soil N transformation varied among different N fertilization conditions, and therefore improve our mechanistic understanding of soil N turnover in a world with huge spatial variations of N enrichment.

The fixation/immobilization and release/remineralization of fertilizer-derived mineral nitrogen (N) to fixed ammonium (NH4+) and organic N pools are crucial in fertilizer utilization and crop N uptake. Although straw mulching reduces the gaseous and leaching losses of fertilizer N from farmlands, the dynamics of fertilizerderived fixed NH4+ and organic N and their roles in fertilizer N retention and supply in soil-crop systems remain unclear. This study utilized 15N-isotope labeling in Northeast China to assess how conventional ridge tillage (RT) and no-till systems with different straw mulch levels (NT0, NT33, NT67, and NT100) affect the accumulation and release of fertilizer-derived fixed NH4+ and organic N. Compared to RT and NT0, no-tillage with straw mulching increased the conversion of fertilizer N to fixed NH4+ and organic N by an average of 15.3 % and 36.5 %, respectively, at a soil depth of 0-40 cm during the maize seedling stage. The higher net release of fertilizer-derived fixed NH4+ (average of 94.1 %) in a 0-40 cm soil layer suggested a high short-term N supply potential from this source during the growing season. Conversely, the limited net release of fertilizersourced organic N via remineralization during the vegetative phase (average of 51.3 %), coupled with the net re-immobilization of fertilizer N from the tasseling to ripening stages (average of 22.9 %), indicated a long-term N supply capacity of fertilizer-derived organic N for subsequent crops. No-tillage combined with straw mulching significantly enhanced fertilizer N use efficiency and maize yield by averages of 10.2 % and 14.8 %, respectively, compared to those of RT and NT0, demonstrating the effectiveness of these practices in optimizing fertilizer application and ensuring high crop productivity. Moreover, these conservation tillage practices enhanced fertilizer utilization and achieved sustainable agricultural outcomes by regulating the conversion and release of fertilizer N to soil-fixed NH4+ and organic N pools and by improving other soil properties.

Different types of organic materials demonstrate varying efficacy in ameliorating saline–alkali soils, while the combined application of organic materials can potentially enhance the remediation effects on saline–alkali land. To verify this assumption, our study conducted a pot experiment with spinach in saline–alkali soil, observing the improvement effect of saline–alkali soil and the growth of crops when acid fermentation products of vegetables, humic acid-like substances, and corn straw were applied either individually or in combination. The results revealed that both the sole and combined application of organic materials could enhance the yield of spinach. Particularly, humic acid-like substances increased spinach yield to six times that of the chemical fertilizer treatment. Although the application of organic materials led to a decline in the diversity and richness indices of the microbial community in saline–alkali soil (except fungal richness), the combined use of organic materials contributed to a healthier trend in the soil microbial community structure. Beyond its effects on soil nutrients such as total carbon and total nitrogen, the improvement in soil organic matter activity caused by the joint application of organic materials was identified as the primary factor responsible for enhancing the health of the soil microbial community and the remediation effects on saline–alkali soil.

Facility-based agriculture has rapidly advanced due to its capacity for high-intensity and year-round crop cultivation. This study evaluated the effects of different nitrogen fertilizer application rates on the growth of greenhouse tomatoes, while utilizing 15N tracing technology to explore nitrogen utilization efficiency during the growth process of facility-grown tomatoes. The results indicate that nitrogen application rates within the range of N60–N80 (93–128 kg N ha−1) can optimally balance yield, nitrogen-use efficiency, and crop growth. Application rates exceeding this range do not enhance yield and lead to reduced nitrogen-use efficiency. Tomato plants exhibited a low N requirement during the seedling stage, relying primarily on native soil N stocks during the flowering stage. Fertilizer-derived N use increased during the fruiting stage. These findings demonstrate that excessive N inputs lead to diminishing returns and potential nutrient imbalances, while fully utilizing soil N stocks during the seedling and flowering stages is essential. This study emphasizes the importance of adjusting nitrogen input according to the developmental stages of the crop to optimize yield and resource utilization.

The fixed ammonium (NH4+-N) pool can serve as a stable transitional reservoir for nitrogen (N) retention and supply in agroecosystems. However, the dynamics of clay mineral-mediated NH4+-N fixation (ANH4) and subsequent release (RNH4ads) processes during the agricultural transition from conventional intensive cultivation to conservation tillage (CT) practices, particularly no-tillage with straw retention (NTS), remain insufficiently characterized. This study integrated 15N-tracing field micro-plot experiments with laboratory incubations to quantify the dynamics of clay mineral-mediated NH4+-N fixation-release turnover in response to 9 years of NTS management in Northeast China. Results revealed that 27.8 % of the applied fertilizer-N was transiently retained as newly fixed 15NH4+-N in the 0-40 cm soil layer during the maize seedling stage. Compared with traditional ridge tillage (RT), NTS significantly enhanced the proportion of newly fixed 15NH4+-N relative to the total applied fertilizer-N, indicating improved N retention capacity during the maize seedling stage. Notably, more than 93.9 % of newly fixed 15NH4+-N was released within the current growing season, with 85.7 % exhibiting rapid release before the tasseling stage, and NTS amplified this pulse release by 6.4 % compared with the RT treatment. In addition, gross transformation rates of both ANH4 and RNH4ads increased by 72.8 % and 101.8 % under the NTS treatment respectively. However, net NH4+-N fixation rates remained statistically comparable among treatments, suggesting intensified clay mineral-mediated NH4+-N fixation-release turnover under CT agroecosystems. Our findings highlight that enhanced clay mineral-mediated NH4+-N fixation-release turnover serves as an effective buffering mechanism by simultaneously improving N retention (9.7 % increase in fertilizer-N use efficiency) and synchronizing soil N supply with crop demand (12.2 % yield enhancement), thereby providing dual benefits of productivity and sustainability in CT agroecosystems of Northeast China.

Reducing fertilizer-N rate, applying a nitrification inhibitor (NI), and incorporating straw are widely recommended to improve N use efficiency of crops and decrease N losses. A field 15N tracer study was conducted to compare their effectiveness on fertilizer-N fates during the maize growing season in Northeast China. The following six treatments were used: (1) no N fertilization (control); (2) 200 kg urea-N ha−1 (100%N); (3) 200 kg urea-N ha−1 and straw (100%N + S); (4) 160 kg urea-N ha−1 (80%N); (5) 160 kg urea-N ha−1 and NI (Nitrapyrin in this study) (80%N + NI); and (6) 160 kg urea-N ha−1, NI, and straw (80%N + NI + S). The results showed that the five N fertilization treatments yielded 16–25% more grain and 39–60% more crop N uptake than the control, but the differences among the five treatments were not statistically significant. Compared with the 100%N, 20% fertilizer-N reduction (80%N) decreased the 15N concentration in topsoil and plant pools but increased the proportion of plant 15N recovery at harvesting (NUE15N, 60% vs. 50%). Compared with the 80%N, NI co-application (80%N + NI) delayed soil nitrification and increased soil 15N retention at harvesting (52% vs. 36%), thereby decreasing NUE15N significantly. Straw incorporation decreased fertilizer-N retention in soil compared with NI co-application because it promoted NUE15N significantly. In conclusion, the results demonstrate that NI and straw additions are efficient strategies for stabilizing fertilizer-N in soils and potentially minimizing N loss; however, their effects on NUE15N vary and the related mechanism must be further clarified in long-term trials.

To reach the target yield of crops, nutrient management is essential. Selecting the appropriate prediction model and adjusting the nutrient supply based on the actual situation can effectively improve the nutrient utilization efficiency, crop yield, and product quality. Therefore, a prediction model of the NPK fertilizer application rate for greenhouse tomatoes under the target yield was studied in this study. Under low, medium, and high soil fertility conditions, a neural network prediction model based on the sparrow search algorithm (SSA-NN), a neural network prediction model based on the improved sparrow search algorithm (ISSA-NN), and a neural network prediction model based on the hybrid algorithm (HA-NN) were used to predict the NPK fertilizer application rate for greenhouse tomatoes. The experimental results indicated that the evaluation indexes (i.e., the mean square error (MSE), explained variance score (EVS), and coefficient of determination (R2)) of the HA-NN prediction model proposed in this study were superior than the SSA-NN and ISSA-NN prediction models under three different soil fertility conditions. Under high soil fertility, compared with the SSA-NN prediction model, the MSE of the ISSA-NN and HA-NN prediction models decreased to 0.007 and 0.005, respectively; the EVS increased to 0.871 and 0.908, respectively; and the R2 increased to 0.862 and 0.899, respectively. This study showed that the HA–NN prediction model was superior in predicting the NPK fertilizer application rate for greenhouse tomatoes under three different soil fertility conditions. Due to the significance of NPK fertilizer application rate prediction for greenhouse tomatoes, this technique is expected to bring benefits to agricultural production management and decision support.

The application of nitrification inhibitors (NIs) and crop straw with nitrogen (N) fertilizers is a common practice aimed at enhancing soil N conservation and improving crop N use. However, their effects on gaseous N emissions from soils, particularly for N2, are less understood. We conducted a 60-day soil incubation experiment under controlled conditions (80

Reducing greenhouse gas (GHG) emissions from agricultural ecosystems is vital to mitigate global warming. Conservation tillage is widely used in farmland management to improve soil quality; however, its effects on soil GHG emissions remain poorly understood, particularly in high-yield areas. Therefore, our study aimed to evaluate the effects of no-tillage (NT) combined with four straw-mulching levels (0 %, 33 %, 67 %, and 100 %) on GHG emission risk and the main influencing factors. We conducted in-situ observations of GHG emissions from soils under different management practices during the maize-growing season in Northeastern China. The results showed that NT0 (705.94 g m-2) reduced CO2 emissions by 18 % compared to ridge tillage (RT, 837.04 g m-2). Different straw mulching levels stimulated N2O emissions after rainfall, particularly under NT combined with 100 % straw mulching (2.89 kg ha-1), which was 45 % higher than that in any other treatments. The CH4 emissions flux among different treatments was nearly zero. Overall, straw mulching levels had no significant effect on the GHG emissions. During the growing season, soil NH4+-N (< 20 mg kg-1) remained low and decreased with the extension of growth stage, whereas soil NO3--N initially increased and then decreased. More importantly, the results of structural equation modeling indicate that: a) organic material input and soil moisture are key factors affecting CO2 emissions, b) nitrogen fertilizer and soil moisture promote N2O emissions, and c) climatic factors exert an inexorable influence on the GHG emissions process. Our conclusions emphasize the necessity of incorporating precipitation-response measures into farmland management to reduce the risk of GHG emissions.

Reducing fertilizer-N rate, applying nitrification inhibitor (NI), and incorporating straw are widely recommended to improve N use efficiency of crops and decrease N losses. However, how these practices affect crop N uptake by regulating the fertilizer-N fate during the growing season is not well understood. We conducted a field 15N tracer study to explore the effectiveness of reduced N application, NI, and straw incorporation on fertilizer-N fates for maize cultivation in Northeast China. The following six treatments were used: 1) no N fertilization (control); 2) 200 kg urea-N ha−1 (100%N); 3) 200 kg urea-N ha−1 and 2400 kg dry-straw ha−1 (100%N+S); 4) 160 kg urea-N ha−1 (80%N, i.e., 20% reduction of N fertilization); 5) 160 kg urea-N ha−1 and nitrification inhibitor (Nitrapyrin) (80%N+NI); 6) 160 kg urea-N ha−1, nitrification inhibitor and 2400 kg dry-straw ha−1 (80%N+NI+S). Our results showed that the five N fertilization treatments yielded 16%–25% more grain and 39%–60% more crop N uptake than the control receiving no N fertilizer, but the differences among the five treatments were not statistically significant. In contrast to plant growth, changes in fertilizer-N fates in soil and plant pools were more pronounced. Compared with the 100%N treatment, 20% fertilizer-N reduction (80%N) decreased 15N concentration in topsoil and plant pools but increased the proportion of plant 15N recovery at harvesting (N use efficiency, NUE15N, 60% vs. 50%) (P < 0.05). Nitrapyrin co-application (80%N+NI) delayed soil nitrification and increased soil 15N retention at harvesting (52% vs. 36%), thereby decreasing NUE15N significantly (P < 0.05). Straw incorporation (100%N+S) decreased fertilizer-N retention compared with NI co-application because it promoted NUE15N significantly (P < 0.05). The combined application of NI and straw (80%N+NI+S) was more conducive to fertilizer-N retention in soil. Our findings demonstrate that NI and straw additions are efficient strategies for stabilizing fertilizer-N in soils and potentially minimizing N loss; however, their effects on NUE15N vary and the related mechanism must be further clarified in long-term trials.

To clarify the effects of maize straw retention combined with reduced fertilization and urease/nitrification inhibitors on the accumulation and leaching potential of mineral N in the deep soil profile of no-tillage agroecosystem. A 15N-tracing micro-plot experiment was conducted with four treatments (NPK, traditional NPK fertilization; NPKS, NPK with maize straw retention; RNPKS, NPKS with 20

Stover mulching in no-tillage farming has been widely proposed as an optimized agricultural management practice to increase soil carbon storage and improve fertilizer nitrogen (N) use efficiency in current agroecosystems. However, the regulation of soil internal gross N transformation dynamics on NO3--N leaching potential in response to long-term conservation tillage practices is still lacking. Here, based on a combination of 15N-tracing incubation and in situ monitoring experiments, we investigated the effect of 9-year no-tillage and maize stover mulching on the vertical migration of fertilizer-derived NO3--N into a deeper soil profile and the associated gross NO3--N transformation dynamics in the Mollisol of Northeast China. The net positive NO3--N production rates (varied from 3.14 to 6.22 mg N kg-1 d-1) were observed across all management practices in the studied Mollisol, indicating a relatively high NO3--N leaching potential in the cropland of Northeast China, which was further confirmed by an average of 7.4 % fertilizer-derived NO3--N being vertically transferred to the 80-100 cm soil layer after a complete maize growing period. Compared with traditional ridge tillage, long-term stover mulching in no-tillage farming significantly reduced total NO3--N production by decreasing autotrophic nitrification while simultaneously enhancing total NO3--N consumption by stimulating nitrate reduction and microbial NO3--N immobilization, revealing a markedly reduction of net NO3--N production in the no-tillage agroecosystem. Therefore, converting traditional ridge tillage toward no-tillage with maize stover mulching can effectively decrease fertilizer-derived NO3--N leaching amounts and thus formulate targeted mitigation strategies for sustainable agriculture in Mollisols of Northeast China.

Mulching has been demonstrated to improve the soil environment and promote plant growth. However, the effects of mulching and mulch-derived microplastics (MPs) on nitrogen fixation by root nodules remain unclear. In this study, we investigated the effects of polyethylene (PE) and polylactic acid-polybutylene adipate-co-terephthalate (PLA-PBAT) film mulching on nitrogen fixation by root nodules after 4 years of continuous mulching using 15N tracer technology. Additionally, we examined the relationship between nitrogen fixation and MPs. We found a reduction in the proportion of nitrogen fixation by nodules (54.3 %-58.7 %) due to mulching. This decrease may be attributed to reduced dinitrogenase activity and flavonoid content at the seedling stage caused by mulching, and mulching with PLA-PBAT films significantly decreased the abundance of Bradyrhizobium at maturity. Furthermore, combined analysis of nitrogen-fixing bacteria (nifH) and metabolomes indicated that N-lauroylethanolamine may act as a regulatory signal influencing the root nodule nitrogen fixation process and that mulching resulted in significant changes in its content. The mantel test and PLS-PM suggest that microplastic from mulching may harm root nodule nitrogen fixation. This study reveals the influence of mulching on plant nitrogen uptake and the potential threat of mulch-derived microplastics, with a special focus on root nodule nitrogen fixation.

Intensified by the pursuit of food security, nitrogen (N) source pollution caused by excessive chemical N fertilizer application has emerged as a major environmental threat, especially through nitrate N (NO 3 - -N) leaching. While no-tillage with straw mulching is recognized for mitigating NO 3 - -N leaching from chemical fertilizer N, its efficacy in deep soil layers remains unclear. Thus, employing the 15 N isotope labeling technique in Northeast China ' s black soil, we investigated the impact of no-tillage and/or straw mulching on the transformation, vertical transport, and leaching loss of fertilizer N under five treatments: conventional ridge tillage (RT), and no-tillage with varying straw coverages (NT-0, NT-33, NT-67, and NT-100). Our results revealed that over 98.3% of fertilizer-derived mineral N in the soil was NO 3 - -N, with substantial downward movement beyond 120 cm, posing a leaching risk. Three years after N fertilizer application, no-tillage and/or straw mulching with varying coverages significantly reduced fertilizer-derived NO 3 - -N by averaging 36.3% in 0 - 300 cm soil profile, compared to RT with 18.36 kg ha -1 fertilizer-derived NO 3 - -N in soil. Notably, no-tillage and/or straw mulching of 33%, 67%, and 100% coverages effectively decelerated the vertical transport of fertilizer-derived NO 3 - -N to 140 - 220 cm soil deeper layers by averaging 48.4%, where NO 3 - -N accumulates in large quantities. The percentages of fertilizerderived NO 3 - -N leached to applied fertilizer N varied from 3.7% to 7.2% after three years of vertical migration. No-tillage with different straw coverages remarkably decreased this leaching percentage by 42.7% and 21.9% compared with RT and NT-0, respectively. Furthermore, we found that no-tillage with straw mulching enhanced fertilizer N utilization efficiency (NUE) and crop yields with NT-33, NT-67, and NT-100 demonstrating higher accumulative NUE of 58.4%, 56.2%, and 58.8% and average yields of 13.90, 13.48, and 13.21 Mg ha -1 , respectively. Therefore, we preliminarily suggest that implementing no-tillage and straw mulching with 33% and 100% coverages in Northeast China holds promise for simultaneously enhancing crop yields and NUE, and mitigating N fertilizer leaching in the form of NO 3 - -N. These findings offer valuable insights for optimizing field management and mitigating N pollution in agriculture, contributing to the achievement of sustainable agricultural development.

Ammonia (NH3) volatilization, a critical pathway of nitrogen (N) loss in agroecosystems, is closely regulated by ammonium (NH4+-N) availability and associated NH4+-N transformation dynamics in soil. To determine the effect of no-tillage and crop stover retention on soil internal gross N transformation and further NH3 volatilization in the long-term conservation tillage (CT) agroecosystem, a combination of N-15-tracing field monitoring and paired N-15-labeled incubation experiments was simultaneously conducted on a 9-year maize cropping system in the Mollisol of Northeast China. Three treatments were set up: traditional ridge tillage (RT), no-tillage with maize stover removal (NT0), and no-tillage with full harvest (ca. 7500 kg ha(-1) yr(-1)) maize stover mulching (NTS). It was found that NH3 volatilization in the experimental Mollisol primarily occurred within 7 days after fertilization. Given that the paired gross NH4+-N transformation dynamics were considered in terms of the mutual production-consumption processes, the low fertilizer-derived NH3 volatilization was mainly attributed to a high gross N transformation rate combined with a low net N transformation rate for all treated plots, indicating that there was a rapid internal NH4+-N turnover in the studied Mollisols. Additionally, no-tillage with maize stover mulching considerably reduced NH3 emissions by 17% compared with RT treatment, and the inhibitory effect was primarily owing to the synchronized stimulation of biotic mineralization-immobilization and abiotic adsorption-release turnover in the CT agroecosystem. These findings suggest that long-term no-tillage with maize stover mulching could be a sustainable management strategy for improving soil NH4+-N retention and mitigating NH3 losses in the Mollisol of Northeast China.