High-concentration phosphorus in pesticide tailwater threatens ecosystem balance due to its toxicity and persistence. While abundant nanosheet structures in LDH(layered double hydroxides)-modified biomass enhance wastewater anion adsorption, optimizing LDH structures to maximize phosphate adsorption and elucidating the underlying microscopic mechanisms require further research. This study employed batch adsorption experiments combined with Response Surface Methodology (RSM) to optimize the synthesis conditions of Mg/Al-LDH modified biochar (MABC). The mechanisms underlying its efficient phosphorus adsorption were systematically investigated through XRD, XPS, FTIR, and SEM characterizations. Results show that MABC6 optimized by RSM (Mg/Al molar ratio 4:1, biochar dosage 10 g·100 mL-1, roasting temperature 450 °C) exhibited high crystallinity, large specific surface area, abundant surface functional groups, and maximum layer spacing, demonstrating optimal adsorption performance (54.932 mg g-1). Chemical adsorption, multilayer adsorption, electrostatic attraction, ion exchange, inner-sphere and outer-sphere surface complexation, and ligand exchange are the main mechanisms of the MABC adsorption process. The optimized MABC6, owing to its increased surface functional groups and expanded layer spacing, promotes multilayer adsorption and ligand exchange while strengthening ion exchange and ligand exchange. This enhances the effective binding between phosphate and adsorption sites. Additionally, soil column experiments indicated that phosphorus-enriched MABC6 (MABC6-P) achieved a cumulative phosphate release rate of 17.59% within 30 days, representing a 50.21% relative increase compared to the raw biochar(BC), highlighting its promising potential for slow-release fertilizer applications. In summary, this study optimized the LDHs-biochar crystalline structure via RSM to expand layer spacing, thereby enhancing adsorption capacity and extending its application in aquatic environmental remediation.

Alternate wetting and drying irrigation (AWD) is widely adopted to save water in crop production, yet it may enhance nitrogen (N) leaching and deep migration in alluvial soil with high water percolation, posing risks to groundwater quality and N use efficiency. A 3-yr field experiment was conducted to elucidate the dual role of biochar in reducing N leaching and reshaping 0-200 cm soil N migration in AWD-managed alluvial soil paddies with three treatments in total, including continuous flooding irrigation (CF) without biochar, AWD without biochar, and AWD with 20 t ha(-1) maize straw biochar. The shift from CF to AWD significantly reduced water percolation by 29 % but increased NO3--N leaching and inorganic N deep migration (100-200 cm) in most cases. AWD combined with biochar lowered water percolation by 36 % over CF alone and reduced inorganic N leaching by 24 % over AWD alone. In addition, AWD combined with biochar increased topsoil (0-40 cm) inorganic N and total N accumulation by 151-280 % while reducing their deep migration (150-2350 %) compared to AWD alone. The reduction in inorganic N deep migration stemmed from the decreased soil solution NO3--N at 120-200 cm, and the enhanced surface soil NH4+-N and inorganic N at 40-100 cm. This study highlights the potential of biochar as a valuable soil amendment that effectively decouples the trade-off between water-saving irrigation and environmental degradation, offering a sustainable strategy for N management in high-percolation cropping systems.

Nitrous oxide (N2O) is recognized as a potent greenhouse gas, and 60% of atmospheric N2O emissions come from cropland soils. Potassium (K) is an important fertilizer for rice paddy fields. K fertilizer decreased the abundance of functional genes mediating nitrification and denitrification processes, thereby mitigating N2O emissions. However, few studies have explored the effect of K fertilization rates on N2O emissions and grain yields, as well as the associated soil properties and aboveground N accumulation in paddy fields under different irrigation regimes. This study aimed to propose an optimum combination of K fertilization rate and irrigation regime to increase grain yield while reducing N2O emissions. Here, a 2-year field experiment using a split-plot design with three replicates was conducted to assess the effect of three K fertilization rates (K0: 0 kg ha-1, K75: 75 kg ha-1, K150: 150 kg ha-1) on N2O emissions, grain yield, aboveground N accumulation, and soil properties, including soil redox potential (Eh), NH4+, NO3-, soil gene abundance of AOA, AOB, nirK, nirS, nirK/nirS, and nosZ, under continuous flooding irrigation (ICF) and alternate wetting and drying irrigation (IAWD). The soil physicochemical properties, the gene abundance and the aboveground N accumulation were evaluated and used to explain how irrigation and K fertilization affect grain yield and N2O emissions. We found that IAWD significantly increased N2O emissions by 38% compared to ICF, and K fertilizer significantly reduced N2O emissions by 15% relative to K0. The effects of IAWD and K fertilizer on N2O emissions can be attributed to the combined impact of soil physicochemical properties and the abundance of functional genes governing N2O emissions. Both irrigation regimes produced equivalent grain yield and aboveground N accumulation. Shifting from ICF to IAWD, the increase in N2O emissions can be mitigated by K fertilization. Moreover, K75 and K150 had similar effects in reducing N2O emissions and yield-scaled N2O emissions, while K75 had a lower K fertilizer cost and higher K partial factor productivity. Therefore, applying K fertilizer at 75 kg ha-1 under IAWD is identified as a potentially suitable rate to secure grain yield while effectively mitigating N2O emissions.

Nano-colloidal particles are the basic units of soil aggregates and play an important supporting role in aggregate stability and water and fertilizer utilization.This study aims to systematically evaluate the regulatory effects of nano-clinoptilolite-based nitrogen fertilizer on paddy soil aggregate structure,rice physiological characteristics,nitrogen utilization,and yield formation.A field split-plot experiment was conducted,with two irrigation modes,conventional flooding(ICF)and alternate wetting and drying irrigation(IAWD)as the main factors,and three sub-factors,including no nano-clinoptilolite-based nitrogen fertilizer(Z0N10),20％nano-clinoptilolite based nitrogen fertilizer & 80％urea(Z2N8),40％nano-clinoptilolite based nitrogen fertilizer & 60％urea(Z4N6).The nano-clinoptilolite-based nitrogen fertilizer used in this study was prepared as follows:Clinoptilolite was dispersed in distilled water and subjected to ultrasonic pulverization.Following pulverization,the supernatant was collected and dried for at least 48 hours to obtain nano-sized clinoptilolite.The prepared nano clinoptilolite was then mixed with an ammonium chloride solution and allowed to adsorb for 2 hours,after which the supernatant was separated.Finally,the nano-clinoptilolite-based nitrogen fertilizer was dried for more than 48 hours until completely dry.To investigate the effects of alternating wetting and drying irrigation and nano-clinoptilolite-based nitrogen fertilizer on the composition of paddy soil aggregates,complete soil samples were collected from the 0-20 cm soil layer of each experimental plot using a five-point sampling method after rice harvest in 2022.After the soil samples were naturally air-dried,they were manually crushed into small pieces according to their natural structure and initially screened through a 10 mm sieve.Subsequently,each sample was graded through sieves of different apertures(5,3,2,1,0.5,and 0.25 mm).The results showed that the wet-dry changes of IAWD caused 1～＜3 mm aggregates to break into micro-aggregates and reduced soil aggregate stability.Nano clinoptilolite-based nitrogen fertilizer effectively increased the proportion of＞0.25 mm macroaggregates,enhanced soil structural stability,and inorganic nitrogen concentration.The application of nano-clinoptilolite-based nitrogen fertilizer significantly increased the effective tillering rate,chlorophyll,and yield of rice.Nano-clinoptilolite-based nitrogen fertilizer also increased the nitrogen accumulation threshold of plants by increasing the inflection point accumulated temperature.Structural equation modelling revealed that the synergistic effect of 80％nano-clinoptilolite based nitrogen fertilizer mixed with 20％urea(Z2N8)was achieved through the path of soil aggregate structure optimization,nitrogen effective supply,and absorption-nitrogen accumulation-driven yield improvement.These findings provide a scientific basis for water resource management and drought mitigation in Northeast China.

Rice-crab coculture (RC) is widely promoted for its high net income but constrained by the need of long-term deep flooding. Herein, we propose a water-saving shallow-water ditch RC model (RCAWD), which applies alternate wetting and drying irrigation (AWD) in rice planting zone, while using crab ditches to support crabs survive water-deficient periods. However, how its implementation affects carbon sequestration, emission reduction, and eco-economics remains unclear. A 3-yr field experiment was conducted to evaluate four cultivation systems: rice monoculture under continuous flooding irrigation (RMCF), rice monoculture under AWD (RMAWD), rice-crab coculture under CF (RCCF), and RCAWD. Compared to RMCF, RCCF significantly increased water use efficiency, and decreased net ecosystem COQ exchange (NEE) over the three years, but it required 14.70% more irrigation water and a strictly continuous flooding environment. In contrast, RCAWD, overcoming the continuous flooding restriction, lowered water usage by 17.19% and elevated water use efficiency by 14.28% over RCCF, and 7.21% NEE decrease, as well as 71.70% CH4 emissions reductions, resulting in carbon emission reduction potential. The increase in carbon sink under RCAWD relative to RCCF is primarily attributed to higher net primary productivity and soil respiration. CH4 emissions reductions under RCAWD further strengthened carbon sink and reduction effect than RCCF, as it increased soil redox potential, soil easily oxidized/dissolved organic carbon compared to RCCF, thereby promoting methanotrophs activity, shifting carbon metabolism to an aerobic process, and inhibiting methanogens. Therefore, RCAWD improved water conservation, carbon sink and CH4 emissions reductions, showing comprehensive advantages.

The interplay between water-saving irrigation and potassium (K) management in regulating paddy methane (CH4) emissions remains poorly understood. It remains unclear whether carbon pool enhancement induced by K fertilization could counteract the oxidation effects under non-flooded irrigation. Here, we conducted a field-based trial over two years to explore how irrigation regimes (continuous flooding, IF; intermittent irrigation, II) and K application rates (K0, K75, K150 kg ha−1) modify soil redox status, carbon pools, crop growth, CH4 emissions and economic benefits. Intermittent irrigation markedly elevated soil redox potential (Eh), suppressed dissolved organic carbon (DOC), and substantially reduced two-year average CH4 emissions by 75.1–76.9%, regardless of K supply. Under IF, high-rate K fertilization (K150) stimulated cumulative CH4 emissions; nevertheless, such K-driven CH4 stimulation was completely offset under intermittent irrigation. Soil Eh, DOC and microbial biomass carbon (MBC) dominated CH4 variation, among which Eh exerted the primary control. Intermittent irrigation combined with K fertilization improved rice grain yield. A comprehensive TOPSIS-Entropy multi-criteria evaluation identified the IIK75 treatment as the optimal option balancing environmental benefits and economic returns. Collectively, intermittent irrigation can mitigate the methanogenic risk from high potassium input, providing a promising redox-regulated strategy for low-CH4 emission and high rice production.

Context: Mulched drip irrigation is an effective strategy for mitigating drought stress and improving peanut production in a dryland cropping system. However, it may alter peanut root architecture, thereby limiting nodule formation and reducing the efficiency of biological nitrogen fixation (BNF). Biochar presents a potential solution to improve BNF efficiency, but its effectiveness varies with feedstock source. Objectives: This study aimed to investigate the effects of two types of biochar on BNF and peanut yield under mulched drip irrigation, to identify the more effective biochar feedstock for enhancing soil quality and crop performance. Methods: A two-year field experiment using a split-plot design was conducted in dryland cropping system to assess the impacts of irrigation method (ICK, drip irrigation; IM, mulched drip irrigation) and biochar treatment (B0, no biochar application; Br, rice straw biochar; Bp, peanut shell biochar) on soil NH4+-N and NO3--N levels, root development, nitrogenase activity, ureide content, dry matter and N accumulation, and peanut yield. Results: Averaged over two years, compared to ICK, IM increased dry matter accumulation by 37 % at flowering, soil NH4+-N content by 113 % at pod filling, nitrogenase activity by 25 % at seedling, ureide content by 30 % at pod filling, and yield by 60 %. However, it decreased root length at flowering and pod filling. Compared to Bp, Br increased soil NH4+-N content by 34-183 %, nodule dry weight by 34-87 %, ureide content by 25-40 %, and peanut yield by 5-15 %, which was attributed mainly to its higher pH, surface area, pore volume, cation exchange capacity, and lower pore diameter. Moreover, soil NH4+-N content, root volume, nodule dry weight, and nitrogenase activity positively correlated with dry matter accumulation, N accumulation, and peanut yield. The Br treatment improved early root growth under IM, enhanced BNF, and increased dry matter and N accumulation, ultimately improving peanut yield. Among all the combined treatments, the IMBr treatment achieved the highest peanut productivity in this area. Conclusions and implications: Compared with the conventional practice (ICKB0), the combination of mulched drip irrigation and rice straw biochar (IMBr) enhanced BNF and peanut productivity. Therefore, we recommend IMBr as an effective strategy to boost peanut production in dryland cropping systems.

Rice-crab co-culture (RC) is increasingly adopted globally to address land resource constraints and nutrient pollution from monocultures, yet few studies have quantitatively characterized nitrogen (N) dynamics in surface water and topsoil, reactive N emissions, rice and crab yield performance, and economic benefits of this ecosystem. A 2-yr field experiment was conducted with three cultural ecosystem, including crab monoculture (CM), rice monoculture (RM) and RC. Results indicated that RC reduced NH3 volatilization by 19.4-22.6%, N2O emissions by 11.5-22.7%, and reactive gaseous N losses by 19.3-22.6% over the two years, compared to RM alone, boosted crab N accumulation and crab yield, but higher gaseous N losses compared with CM alone. In comparison with the combined outputs of CM and RM, RC utilized only approximately half of land and water resources, but produced comparable rice yield, 0.8-1.7% higher crab yield, and 35.7-271.4% net economic benefits with 19.3-22.6% lower reactive gaseous N losses. The 19.3-22.6% reduction in gaseous N losses under RC over RM was mainly associated with enhanced soil inorganic N retention and reduced NH4+-N concentration in surface water. In conclusion, RC effectively mitigates reactive gaseous N losses while delivering substantial economic benefits compared to RM and CM, positioning it as a sustainable and economically viable alternative for intensive agricultural ecosystems facing resource scarcity and environmental pollution challenges.

Traditional water-nitrogen models cause high nitrogen loss, carbon emissions, and low efficiency. To balance peanut yield, efficiency, and carbon reduction, a two-year split-plot field experiment was conducted with "Nonghua 9". Main plots were full irrigation (W0) and regulated deficit irrigation (W1); subplots were four nitrogen (N) rates (0-150 kg center dot hm- 2). Ammonia volatilization (AV), C/N accumulation and transformation, carbon balance, N use efficiency, and yield were evaluated across the treatments. The results showed that cumulative AV peaked on day 3 postfertilization and correlated positively with N rate. W1 reduced AV loss at equivalent N levels. W1 combined with 100 kg center dot hm- 2 nitrogen application (W1N2) significantly increased carbon and nitrogen concentrations in leaves and stems and promoted the translocation of carbon and nitrogen to pods. The leaf and stem C/N ratios remained optimal (16.18-32.18 and 13.11-31.77). The nitrogen nutrition index (NNI) of the W1N2 treatment remained close to 1 throughout the growth, indicating balanced N supply. Soil CO2 emission flux peaked at flowering stage. W1 reduced the average and cumulative CO2 emissions across stages, whereas higher N rates increased emissions. All treatments acted as carbon sinks, with W1N2 achieving the highest net ecosystem productivity (CNEP; 140.3%-154.3% higher than W0N0). and maximum yields (5850.08-5930.88 kg center dot hm- 2), along with superior agronomic nitrogen use efficiency, pod nitrogen uptake efficiency, and apparent recovery efficiency were significantly. In conclusion, W1N2 provides a feasible water-nitrogen strategy for green and low-carbon peanut production in drylands.

Biochar application can improve soil conditions, enhance nutrient uptake, and increase crop productivity, particularly under water stress. However, the comparative effects of biochar derived from different feedstocks on peanut growth and yield remain unclear. A two-year pot experiment was conducted to examine the impacts of maize straw biochar (BM) and wood chip biochar (BW) on peanut growth, nutrient uptake, water use efficiency (WUE), and soil nitrogen (N) and potassium (K) availability under three irrigation regimes: well-watered (IWW), moderate water stress (IMS), and severe water stress (ISS). Water stress (IMS and ISS) increased soil NH4+ -N, NO3 --N, and available K relative to IWW, likely due to reduced plant nutrient uptake. Nevertheless, total N and K uptake by plants declined under stress, leading to 15.7-47.5% yield reductions. Biochar application mitigated these effects, improving plant height by 5.3-18.2%, leaf area by 4.1-13.4%, N uptake by 2.8-20.0%, K uptake by 11.6-21.6%, yield by 10.1-54.6%, and WUE by 1.4-46.0%, compared with the control. Notably, BW outperformed BM in promoting nutrient uptake and yield, particularly under stress, due to its higher intrinsic N and K, and superior cation exchange capacity. The IMSBW combination produced the highest N and K uptake and yield, achieving yields comparable to well-watered controls (IWWB0) but with reduced water use, resulting in significantly higher WUE. These results suggest that wood chip biochar application under moderate water stress offers a sustainable strategy to enhance peanut productivity in arid regions.

Context: Rice-aquatic animal coculture leverages ecological synergies to improve nutrient cycling. However, the potassium (K) utilization and balance, critical determinants of system sustainability, remain poorly understood. Objective: A two-year field experiment was conducted in Liaoning Province, the primary hub for the rice-crab coculture system in China. We present the first comprehensive investigation to quantify soil available K, K utilization, environmental K losses, system-level balances, yield, and the economic benefits of rice-crab coculture. Results: Results showed that rice-crab coculture significantly enhanced K retention. Soil exchangeable K was 5.23-7.06 % higher, and soil solution K+ concentrations in subsurface layers (20-40 cm) were 13.79-16.61 % higher than in rice monoculture. The system exhibited significantly higher aboveground K uptake in rice while supporting crab production, although K leaching was 14.43-24.49 % higher, a trade-off offset resulting from substantial K balance improvements. Crucially, rice-crab coculture exhibited superior K sustainability, with 13.51-15.77 % and 16.83-18.78 % higher apparent and total K balances, respectively, than in rice monoculture. Partial least squares path modeling identified aboveground K uptake and soil exchangeable K as pivotal drivers of total K balance in the rice-crab coculture system. Additionally, rice-crab coculture achieved significantly higher economic benefits than rice monoculture through obtaining additional crab yield without affecting rice yield. Conclusions: These findings demonstrated the potential of rice-crab coculture to enhance K utilization and reduce K deficiency while providing considerable economic benefits. The results provide insights for developing policies and encouraging more farmers to adopt rice-crab coculture. Significance: The study established a quantitative framework for optimizing K management in coculture systems, a crucial advancement for increasing the sustainability of the rice-aquaculture frontier.

Urease and nitrification inhibitors effectively mitigate nitrogen (N) losses in paddy ecosystems, yet their efficacy and interactive effects under alternate wetting and drying (AWD) with fluctuating soil moisture remain poorly understood. Here, we conducted a three-year field-based lysimeter experiment (2021-2023) with five treatments: continuous flooding irrigation (CF) with no inhibitor (ICFA0), AWD with no inhibitor (IAWDA0), AWD with a nitrification inhibitor dicyandiamide (DCD) (IAWDAN), AWD with a urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) (IAWDAU), and AWD with both inhibitors (IAWDAN+U). AWD had no significant effect on NH3 volatilization compared to CF, but it increased total N leaching by 15.1%-26.5% over three years. The sole application of NBPT under AWD significantly reduced NH3 volatilization and N leaching by 19.1-43.2% and 1.3-14.1%, respectively. However, DCD significantly increased NH3 volatilization by 5.8-25.1% and N leaching by 15.2-27.9% under AWD. Notably, the combined application of two inhibitors (NBPT and DCD) under AWD decreased NH3 volatilization by 6.0-38.5% and N leaching by 3.5-28.3%. Soil NH4+ availability and urease activity jointly regulated NH3 volatilization and N leaching under AWD conditions. Neither inhibitors nor AWD significantly affected grain yields. Our findings demonstrate that no single inhibitor regime is universally optimal under AWD: dual application balanced N leaching control, while NBPT alone achieved stronger NH3 volatilization mitigation. These results emphasize the need to tailor inhibitor strategies to specific N loss mitigation targets in AWD rice systems.

Current rice production faces a critical trilemma of ensuring food security while conserving water and mitigating climate impacts. Conventional irrigation and nitrogen application sustain yields but simultaneously exacerbate water scarcity and environmental burden. Addressing this challenge requires urgently reconciling trade-offs among food security, water conservation, and climate regulation through optimized water and nitrogen management. Here, a two-year field experiment was conducted to evaluate the effects of alternate wetting and drying irrigation (AWD) and nitrogen-loaded biochar (NLB, 20 t ha−1) on rice yield, water consumption, ammonia volatilization, and nitrogen distribution along the “soil–rice–plant” continuum. We found that AWD significantly reduced water consumption by 14.17–15.56

The development of low-carbon, water-efficient rice cultivation systems is crucial for sustainable agriculture. Nevertheless, although alternate wet-dry irrigation (IAWD) can save water and promote the mineralization of soil organic nitrogen (N), it may reduce soil organic carbon (SOC) sequestration and increase ammonia (NH3) volatilization. To address this trade-off, a magnesium-modified biochar-based fertilizer (MBF) was applied to optimize biochar's inherently high C:N ratio while enable controlled nitrogen release. A two-year field split-plot experiment was conducted to evaluate the effects of two irrigation regimes (main plots) and five fertilization practices (subplots) on SOC, soil inorganic N, water-N use efficiency, yield, and NH3 emissions. Results showed that IAWD combined with N fertilizer reduction and MBF enhanced stem/leaf-tograin N translocation through the modulation of crop growth rates, increasing yield and grain N use efficiency (NUEg). Correlation analysis demonstrated that higher soil NH4+ -N suppressed SOC priming, while reduced NH4+-N during basal fertilization and increased SOC limited NH3 emissions and improved water use efficiency (WUE). Structural equation modeling indicated NH3 emissions directly reduced NUE and indirectly affected WUE. Compared with conventional fertilization, the treatment of 25 % N reduction combined with 10 t ha-1 MBF (N3/4B2) increased SOC by 14.40 %, optimized NH4+-N distribution (reduction during basal fertilization but enhancement during topdressing periods), reduced NH3 emissions by 10.78 %, and increased yield by 4.82 % and WUE by 10.86 % (two-year averages). Thus, TOPSIS modeling confirmed IAWDN3/4B2 as a sustainable strategy integrating water-saving, yield stability, carbon sequestration, and NH3 mitigation.

Rice-aquatic animal coculture enhances nutrient cycling via ecological synergies, yet its negative potassium (K) balance caused by leaching and long-term crop residue removal remains a bottleneck for maintaining paddy K sustainability. Here, maize straw-derived biochar was applied back to rice-crab coculture (RC) paddy to explore the feasibility of reversing the negative K balance. We measured soil K fractions, K leaching and utilization, and evaluated the K balances treated with rice monoculture (RM), RC, and RC with 20 t ha⁻1 maize straw-derived biochar (total K: 1.38%) application at once (RCB). RC significantly increased soil solution K (0–40 cm), exchangeable K, and K balances compared with RM, but elevated K leaching and failed to address the negative K balance. RCB increased soil solution K (0–20 cm), exchangeable and non-exchangeable K, boosted aboveground K uptake and crab K accumulation, and lowered K leaching by 15.92%, compared to RC, shifting total K balance from −77.27 kg ha−1 to 237.15 kg ha−1. Partial least-squares path modeling further revealed biochar-originated K input and soil exchangeable K as the two dominant drivers governing total K balance. Although upfront biochar purchase costs lowered net income for RCB relative to RC, RCB still delivered higher net income than RM. Collectively, biochar integration within RC curtails K loss, strengthens soil K retention and transforms negative K budgets into positive ones, though these findings are limited to a single experimental site, biochar feedstock and fixed application rate, so targeted regional field trials are required to validate its universal practicability.

Introduction Alternate wetting and drying irrigation (IAWD) is a promising practice for water conservation and climate mitigation, yet it inadvertently stimulates substantial nitrous oxide (N2O) emissions. While previous research has largely focused on surface N2O fluxes, the processes governing N2O accumulation and emission across the soil profile-surface continuum remain poorly understood.Methods Here, we present a comprehensive dataset from a lysimeter study on paddy fields under IAWD and continuously flooded irrigation (ICF), integrating measurements of soil N2O concentrations (0-50 cm depth, at 10-cm intervals) and concurrent surface fluxes.Results The results showed that N2O predominantly accumulated in 0-20 cm soilprofiles during the tiller fertilizer period (TF) and panicle fertilizer period (PF) regardless of the irrigation regimes. Compared to ICF, IAWD significantly increased the N2O concentrations in 0-30 cm soil profiles by 19.6-49.3% and 60.0-79.0% during the TF and PF, respectively. Partial least-squares path model further identified the 10-20 cm layer as the dominant hotspot, exerting the strongest direct control on surface N2O emissions.Discussion Altogether, 0-20 cm soil profiles are the hotspots for N2O accumulation in IAWD paddy fields, and the N2O accumulated in 10-20 cm soil profile dominates the N2O emissions. These findings contribute to the adoption of straightforward and targeted N2O mitigation strategies in IAWD paddy fields.

Biochar has been recognized to deliver several benefits in field crops. However, its impact on phosphorus (P) leaching, distribution, and deep migration in paddy fields under alternate wetting and drying (AWD) irrigation remains unclear, especially in a typical alluvial plain. A 2-year field experiment was conducted with three treatments: continuous flooding irrigation without biochar, AWD without biochar, and AWD with 20 t ha-1 maize straw biochar. A multi-layer device together with a bottom-sealed polyvinyl chloride bucket was used to monitor dissolved P dynamics and P leaching. And a four-stroke gasoline-powered soil sampler was employed to collect data on the distribution and migration of soil available P and total P along the 0-200 cm soil profile. The shift from continuous flooding irrigation to AWD reduced water percolation by 25 %-38 % but increased soil available P deep migration (100-200 cm). Under AWD, biochar addition further decreased water percolation by 9 % and reduced dissolved P leaching by 20 % compared with AWD alone. Moreover, biochar increased soil available P by 141-277 % and total P migration by 133-219 % at 0-40 cm and while inhibiting the deep migration of soil available P by 119 %-1114 % and that of total P by 210 %-2644 %. The reduced soil available P deep migration with biochar was mainly caused by the decreased soil total P in the 100-200 cm soil profile. Our results provide a novel approach for sustainable P management in agricultural ecosystems, offering critical insights into the role of biochar in regulating nutrient dynamics in paddy soils.

Context or problem: This study explores the development of an efficient, eco-friendly nano-biochar-based struvite (NBS) fertilizer by enhancing slow-release properties and nanocolloid content of biochar-based fertilizers through ultrasound-assisted magnesium modification. Objective or research question: The NBS fertilizer is designed to partially replace urea at low doses, reducing the environmental impact of fast-release fertilizers while promoting nitrogen (N) balance in the soil-crop system. Methods: A two-year field experiment was conducted to evaluate the effects of different NBS substitution rates (0 %: CF, 10 %: B1N9, 30 %: B3N7) on soil aggregate stability, ammonia (NH3) volatilization, warming potential, soil apparent N balance, crop N uptake, yield, and net ecosystem economic benefits (NEEB). The critical N concentration dilution curve model and N nutrition index (NNI) were used for assessment. Results: The results showed that the treatments of replacing partial urea with NBS (BN treatments) significantly reduced cumulative NH3 emissions by 19.64-35.20 %, lowering the warming potential by 14.85-31.93 kg CO2-eq ha(-1). Floodwater NH4+-N concentration played a stronger role in influencing NH3 volatilization than floodwater pH. Increasing NBS application improved soil aggregate stability by enhancing the proportion of > 250 mu m water-stable aggregates, thereby improving N retention. The BN treatments reduced soil apparent N loss by 21.32-41.84 %, and resulted in NNI values between 0.88 and 1.00, indicating balanced crop N utilization. Replacing 10 % urea with NBS (B1N9) led to displayed stronger N assimilation than the 30 % substitution (B3N7) under identical dry matter conditions. The B1N9 treatment also increased yields by 15.02 %, and improved NEEB by 4.38 % (two-year average). Conclusions: Based on these findings, we recommend applying NBS to replace 10 % of urea to enhance agricultural sustainability and profitability.

Nanotechnology enhances biochar functionality but introduces environmental toxicity risks, prompting the development of iron (Fe)-modified biochar to improve magnetic recovery and reduce ecological impacts. However, balancing enhanced magnetic recyclability with adsorption capacity remains a challenge. This study innovatively resolves the critical dilemma between magnetic recyclability and adsorption performance through magnesium (Mg) doping in ball-milled magnetic nano-biochar composites. The resulting material exhibited multifunctional improvements. Mg incorporation increased ammonium nitrogen and phosphate adsorption capacities by 2.85-fold and 1.18-fold respectively, while amplifying magnetic strength by 4.91-fold compared to conventional Fe-modified counterparts. Structural and mechanistic analyses revealed that Mg doping enriched pi-pi configurations, hydroxyl/metal oxide groups, and electron transfer efficiency. It also promoted the formation of ferrimagnetic phases (MgFe2O4 and (MgO)0.77(FeO)0.23) critical for magnetic enhancement. Semi-quantitative contribution analysis highlighted Fe's dominance in magnetic recovery (45.3 %) and Mg's superior adsorption role (53.4 %), with complementary synergies in both functions. By overcoming the conflict between recyclability and adsorption, this magnesium-doped composite establishes a sustainable method for wastewater remediation, enabling simultaneous nutrient recovery and material reuse cycles. The findings provide a design framework for multi-functional environmental materials through strategic elemental doping, advancing sustainable water remediation.

Contrasting effects of straw and biochar with equivalent straw input on ammonia volatilization and N leaching under alternate wetting and drying irrigation (IAWD) in paddy ecosystems are limited. A 2-yr paddy buried pot experiment was conducted with annual rice straw and single biochar applications with equivalent straw input under continuously flooded irrigation (ICF) and IAWD. Four treatments comprising no amendment under ICF (ICFA0), no amendment under IAWD (IAWDA0), rice straw (29.41 t ha(-1) yr(-1)) under IAWD (IAWDAS) and biochar (20 t ha(-1) applied once) under IAWD (IAWDAB) were arranged in a randomized complete block design. IAWD did not significantly alter ammonia volatilization, but increased N leaching. Compared with ICFA0 and IAWDA0, IAWDAS significantly increased ammonia volatilization by 7.92-52.71% and decreased yield by 22.98-31.87% in both years, but increased N leaching by 31.18% in 2021 only. IAWDAB increased ammonia volatilization, N leaching and reactive N losses in 2021 but significantly decreased reactive N losses in 2022 compared with no amendment. IAWDAB reduced grain yield due to the increased reactive N losses in 2021. Both IAWDAS and IAWDAB improved soil total N. IAWDAB had higher yield and N uptake, and lower reactive N losses than IAWDAS. Overall, biochar is a more effective strategy for reducing reactive N losses in IAWD paddy systems over time. Direct straw return could take longer for its decomposition or be annually applied at a lower rate to address its higher reactive N losses and lower grain yield after a 2-yr consecutive annual application.