The stable nitrogen isotopic composition (S15N) is widely used to trace and quantify sources of atmospheric ammonia (NH3). However, the complexity of emission sources and the lack of S15N-NH3 values from different sources introduce high uncertainties in estimating the contribution of the individual source to atmospheric NH3. In this study, we conducted a comprehensive two-year field observation of NH3 concentrations and S15N-NH3 values from various emission sources, including vegetables, orchards, rice-wheat rotations, rural residential areas, and aquaculture, within an agricultural river network area in Southeast China. Our observations revealed that the mean NH3-N concentrations were highest for orchards (6.7 f 3.1 mu g m- 3) and the lowest for aquaculture (5.2 f 2.1 mu g m- 3). The annual mean S15N-NH3 values varied across sources, with values of -33.9 f 3.5 %o for vegetables, -35.2 f 3.7 %o for orchards, -35.7 f 3.1 %o for rice-wheat rotations, -33.3 f 3.5 %o for rural residential areas, and -34.4 f 2.6 %o for aquaculture. Fertilization activities significantly increased agricultural NH3 concentrations while decreasing their S15N-NH3 values. Scenario simulations using the Bayesian isotope mixing model showed that the inclusion of all five agricultural emission sources resulted in a 27.9 % increase in the contribution of agricultural NH3 to atmospheric NH3 compared to simulations assuming a single source, whereas the types and numbers of industrial sources remained unchanged. These findings demonstrated the importance of identifying both the types and numbers of local sources and monitoring their S15N-NH3 values for improving the traceability of atmospheric NH3.

Soil multifunctionality is the key to maintain soil health and develop sustainable agriculture. Soil microbiomes are crucial for regulating numerous functions, but how soil multifunctionality are driven by the shifts of microbial communities and nutrient supplies in agricultural ecosystems remains unclear. Moreover, the relationships between soil multifunctionality and cropland productivity have not been fully understood. To address these knowledge gaps, we conducted field experiments including different nitrogen (N) application rates in four sites of Northeast China with a gradient of climatic conditions and soil organic carbon (SOC). Soil functions related to SOC, N, phosphorus, and bacterial and fungal diversity, community composition, network complexity, and stability were combined to quantify soil multifunctionality. We found that soil multifunctionality accounted for approximately 20 % of variations in maize production. SOC was the most important predictor of multi-functionality. SOC content and fractions, including readily oxidizable carbon, carbohydrate, and lignin, were primary factors shaping the soil microbial communities. In addition, the larger impact of SOC on bacterial communities resulted in greater roles of bacterial diversity and network complexity in supporting soil multi-functionality compared to fungi. The higher SOC also shifted microbial community composition, increasing the abundances of dominant bacterial phyla Acidobacteriota and Chloroflexi, with Acidobacteriota showing a strong positive correlation with soil multifunctionality. PLS-PM results revealed that soil multifunctionality directly and positively affected N use efficiency (NUE), turn to enhance crop productivity. These findings highlight the contribution of soil multifunctionality to cropland productivity, as well as the importance of SOC and the bacterial community in sustaining ecosystem functions in croplands.

Nitrogen input is commonly used as an indicator of environmental pressure in intensive pond aquaculture. However, its ultimate environmental effects depend on how nitrogen is partitioned among harvested products, effluent discharge, gaseous losses, and pond sediments. Whether a linear relationship exists between high input levels and high pollution remains to be determined. This study compared a high-input crab–shrimp polyculture pond (C–SP) with a low-input shrimp pond (SP) in eastern China. Nitrogen inputs and fates; ammonia (NH3), nitrous oxide (N2O), and methane (CH4) emissions; harvest revenue; explicit direct production costs; and direct environmental damage cost (EDC) were quantified. The results showed that the total nitrogen input was 409.33 kg N hm-2 in C–SP, 34.83% higher than the 303.60 kg N hm-2 recorded in SP, primarily because of greater feed-N input. Nitrogen recovered in harvested products was also higher in C–SP than in SP (37.09 vs. 23.45 kg N hm-2). Sediment accumulation represented the largest quantified nitrogen sink in both systems, accounting for 219.36 kg N hm-2 in C–SP and 169.87 kg N hm-2 in SP, whereas unaccounted nitrogen amounted to 116.68 and 68.61 kg N hm-2, respectively. The combined nitrogen output through effluent discharge, NH3 volatilization, and N2O emissions was lower in C–SP than in SP (36.20 vs. 41.68 kg N hm-2). Their global warming potentials were 1,734.48 and 2,145.70 kg CO2-eq hm-2, respectively. Harvest revenue reached 224.25 × 103 CNY hm-2 in C–SP, exceeding the 158.91 × 103 CNY hm-2 obtained from SP. Meanwhile, the estimated EDC was lower in C–SP than in SP (0.31 × 103 vs. 0.37 × 103 CNY hm-2). These results demonstrate that greater nitrogen input did not result in higher measured immediate environmental releases through gaseous emissions and effluent discharge; instead, more nitrogen was recovered in harvested products or retained in pond sediments. Thus, when a larger proportion of nitrogen input is recovered in aquaculture products or temporarily retained within ponds, high-input systems may achieve both higher economic returns and a lower directly quantified environmental burden. The findings provide empirical evidence for achieving synergistic gains between high nitrogen input and high economic benefits in aquaculture systems.

Nitrification inhibitors (NIs) are widely used to mitigate nitrous oxide (N2O) emissions from agricultural soils. However, its efficiency is highly uncertain owing to varying environmental conditions and still-debated inhibition mechanisms, especially the responses of the nitrifiers and denitrifiers responsible for N2O production. Here, we conducted microcosm incubations to investigate the comparative effectiveness of three NIs (DCD, DMPP, and nitrapyrin) on N2O emissions from cultivated Mollisols under contrasting moisture levels (60 % and 90 % water-filled pore space, WFPS). The soil nitrification rate, N2O-related gene abundance, and community composition of ammonia-oxidizing bacteria (AOB) were determined. The results showed that all NIs effectively inhibited nitrification, with DCD and DMPP having higher efficacy than nitrapyrin, regardless of soil moisture conditions. Interestingly, a greater decrease in N2O emissions was observed under 90 % WFPS than 60 % WFPS (39.0-47.6 % vs. 26.8-31.9 %). NIs selectively decreased the amoA gene abundance in AOB rather than in ammonia-oxidizing archaea. The most abundant AOB (> 90 %) belonged to Nitrosospira. RDA analysis revealed that the AOB Nitrosospira cluster 3a had the greatest relationship with N2O emissions, and its abundance was significantly decreased with NI amendments. Moreover, non-target denitrifying genes (nirS and nirK) were suppressed, particularly at high moisture levels, which further contributed to reduced N2O emissions. Overall, our findings highlight the significant role of environmental conditions, keystone species of AOB, and non-targeted effects on denitrifiers on the efficacy of NIs. Additionally, these results imply that NIs are a potent option for fertilizer management to mitigate N2O emissions and that DCD and DMPP have promising prospects for the cultivated Mollisols agro-system under climate change with intensifying extreme rainfall events.

The global food crisis provides an impetus for agricultural green transformation via optimized fertilization methods. While organic substitution, green manure incorporation, and targeted fertilization sites have individually shown promise in enhancing rice yield, there is still a gap between optimized fertilization methods and achieving sustainable rice production. To explore the factors influencing rice yield across different fertilization strategies, we conducted a field experiment in Southern China encompassing five treatments, such as CK (no N input), RN (broadcasting urea with recommended N rates), RON (broadcasting organic-inorganic fertilizer with recommended N rates), RONS (side-deep placement of organic-inorganic fertilizer with recommended N rates), and RONSA (coupled RONS with Azolla [Azolla pinnata R. Brown]). Using a Minimum Data Set approach, we identified the primary variables influencing soil properties and rice production, with a focus on soil physicochemical characteristics and bacterial communities. Further, the soil properties index (SPI), calculated by multiplying the linear score with the weight of each variable, served as an indicator of soil properties variations. Our findings revealed that RONSA significantly increased the SPI by 21.1% compared with RN, predominantly because of higher soil labile organic carbon (LOC) and available N (SAN) fractions (p < .05). N uptake in rice plants (23.9%-28.4%) increased dramatically under RONSA leading to higher rice yield (11.0%-16.9%) and NUE (30.2%-36.1%) than RN (p < .05). The enhancement in soil properties, characterized by increased LOC, SAN fractions, and bacterial community diversity, was essential in boosting rice yields, with dissolved inorganic N emerging as the dominant contributor. In summary, our results highlight the effectiveness of integrated fertilization approaches in enhancing soil properties, subsequently leading to improved rice yields and NUE. This fertilizer strategy holds promise for guiding field fertilization practices and advancing sustainable rice production.

AbstractInvestigating the sources of ammonia (NH3) in the atmosphere and the contribution of each source is essential for environmental pollution control. The presented dataset aims to provide 15N natural abundance (δ15N) data collected from different controlled treatments to fill the knowledge gap between insufficient data of soil δ15N-NH3 and accurately identifying atmospheric NH3 source apportionments. Our results showed that the overall δ15N-NH3 values emitted from soil ranged from −46.09 to 10.22‰, with an average of −26.81 ± 11.17‰. The mean δ15N-NH3 values under different nitrogen (N) application rates, N fertilizer types, air temperatures, soil moisture, soil pH, soil types, and land use types were −29.41 ± 10.91, −32.43 ± 6.86, −29.10 ± 10.04, −30.31 ± 6.18, −24.84 ± 13.76, −23.53 ± 7.66, and −14.57 ± 12.54‰, respectively. Significant correlations were observed between δ15N-NH3 values and soil pH, soil NO3−-N concentration, and NH3 volatilization. This unique database provides basic data and evidence for the qualification of atmospheric NH3 source apportionments under different study area conditions.

红萍对水体铵态氮浓度较为敏感,稻田放养红萍模式下,红萍的生物固氮作用及其抑制氨挥发的作用对不同施氮量的响应未知.红萍为水生蕨藻共生体,具有很强的生物固氮能力.红萍可作为优质绿肥放养于稻田,以替代部分化学氮肥,起到节能减排的效应.为明确稻田养萍模式下不同施氮量对红萍生物固氮作用和田间氨挥发的影响,采用盆栽试验设置了0、75、150、225、300 kg/hm2共5个施氮(以纯N量计)水平,监测了稻田放养红萍和水稻单种各处理的氨挥发量、生物固氮速率和水稻产量.结果表明:①同一施氮水平下,稻田放养红萍可显著降低氨挥发日通量峰值及氨挥发总量.在施氮量为225 kg/hm2时,稻田放养红萍对氨挥发总量的抑制作用最大,与水稻单种相比,抑制幅度可达83.2％.②红萍的生物固氮速率及固氮总量与施氮量呈线性负相关关系,随施氮量的增加,固氮速率和固氮量逐渐降低,施氮量300 kg/hm2并放养红萍处理得到的固氮速率及总量同不施氮肥不养萍处理之间无显著差异.③与不养萍处理相比,放养红萍组各处理的水稻产量都明显增加,其中施氮量为225 kg/hm2时水稻增产幅度最大,增幅达21.2％.综上,在施氮条件下,稻田养萍可显著抑制稻田氨挥发并提高水稻产量,随着施氮量的增加,红萍作为生物绿肥的固氮作用受抑制程度加重.在不牺牲水稻产量的前提下,稻田养萍可替代约75 kg/hm2的化学氮肥,且能抑制83.2％的稻田氨挥发.

Tillering nitrogen (N) topdressing is commonly employed to enhance primary-tiller number and achieve a high grain yield for wetland rice. Unfortunately, farmers typically apply N fertiliser shortly at tillering initiation following basal fertilisation, and substantial soil ammonia (NH3) volatilisation occurs due to the low N demand of small plants. Herein, we hypothesised that delaying topdressing N until the midtillering phase could increase canopy recapture of soil NH3 emission and better synchronise N supply with crop N demand, leading to reduced NH3 losses and increased fertiliser N use efficiency. A field experiment was conducted to investigate the effect of conventional tillering N topdressing (CT) at the early tillering stage (2 weeks after basal N application) and delayed tillering N topdressing (DT) until the midtillering phase (∼4 weeks after basal N application) on NH3 emission from soil and the soil-plant system, as well as N uptake, N use efficiency and yield. The 2-year field results showed that DT did not hinder effective tiller production or above-ground dry biomass compared with CT, but improved plant N uptake and total N accumulation after midtillering, leading to 18–27 % higher agronomic efficiency. Correspondingly, 8.9–15 % increases in grain yield were observed for DT compared with CT, mainly attributable to increased panicle number per area and filled grain number per panicle. Following tillering N application, NH3 loss from the soil-plant system under CT accounted for 22 % of top-dressed N, showing only a slight decline compared with that of soil emission. For DT, NH3 loss from the soil-plant system was reduced to 6 %, even though 15 % soil NH3 emission was observed, indicating a more than two-fold increase for in-canopy NH3 recapture. Correspondingly, cumulative net NH3 losses for the entire rice season were decreased by 31% under DT relative to CT. These results provide evidence that delaying tillering N topdressing until the midtillering phase when rice canopy formation is enhanced, can better synchronise fertiliser N supply with crop demand and increase in-canopy NH3 recapture. A large discrepancy remains between NH3 emission from soil and the soil-plant system at midtillering and panicle initiation stages, highlighting the overestimation by the soil dynamic chamber method when quantifying NH3 losses due to overlooking the contribution of canopy recapture of soil-emitted NH3.

Elevated CO2 (eCO2) strongly affects rice yield and quality in arsenic (As) paddy soils. However, understanding of the As accumulation in rice under coupled stress of eCO2 and soil As is still limited while data are scarce. It greatly limits the prediction for future rice safety. This study investigated the As uptake by rice grown in different As paddy soils under two CO2 conditions (ambient and ambient +200 mu mol mol-1) in the free-air CO2 enrich-ment (FACE) system. Results showed that eCO2 lowered soil Eh at the tillering stage and caused higher con-centrations of dissolved As and Fe2+ in soil pore water. Compared with the control, the increased As transfer abilities in rice straws under eCO2 contributed to the higher As accumulation in rice grains, and their total As concentrations were increased by 10.3-31.2%. Besides, the increased amounts of iron plaque (IP) under eCO2 failed to effectively inhibit the As uptake by rice due to the difference in critical stage between As immobilized by IP (mainly in maturing stage) and uptake by rice roots (about 50% contribution before filling stage). Risk as-sessments suggest that eCO2 enhanced the human health risks of As intake from rice grains produced in low-As paddy soils (<30 mg kg-1). In order to alleviate the As threats to rice under eCO2, we consider that proper soil drainage before filling stage to improve soil Eh can serve as an effective way to reduce As uptake by rice. Pursuing appropriate rice varieties to reduce the As transfer ability may be the other positive strategy.

The rising atmospheric CO2 is a major driver for climate change, directly affects rice production. Cadmium (Cd) in paddy soils also serves as a persistent concern. Currently, few studies consider the rice response to coupled stresses of elevated CO2 (eCO2) and soil Cd. Experimental evidence understanding the effects and mechanisms of eCO2 on Cd uptake by rice is lacking yet. In a free-air CO2 enrichment (FACE) system, a 3-year pot experiment was conducted to explore the Cd uptake by rice under two CO2 conditions (ambient and ambient + 200 mu mol.mol- 1) using combinations of in-situ Cd-contaminated soils and associated rice varieties. Results showed that more low-crystalline Fe oxides (Feh) in iron plaque (IP) were deposited on root surface with the increased dissolved Fe2+ due to lower soil redox status under eCO2. The Cd accumulation in rice was hindered due to more Cd associated with Feh (Feh-Cd) rather than uptake by roots. Taken together, the relative effects of eCO2 on Cd uptake by rice were consistent across years under different Cd-contaminated soils. Our findings will help to better understand the Cd uptake by rice under future climate conditions, and thus push the development of climate -crop-soil models and accurate prediction for food security.

Ammonia (NH3) is one of the most important sources that have been linked to the formation of PM2.5. Therefore, it is important to study the source contributions to atmospheric NH3 for air pollution control. Here we used 15N natural abundance (expressed by δ15N) values to quantify the source contributions to atmospheric NH3 in the Beijing-Tianjin-Hebei (BTH) region, which suffers from the country's worst air pollution. Results showed that from 2017 to 2019, the annual mean δ15N-NH3 value at the livestock site (-27.5 ± 6.0 ‰) was lower than at cropland (-20.7 ± 6.0 ‰) and rural residential sites (-22.1 ± 7.4 ‰), while their concentrations were the opposite. Seasonal mean δ15N-NH3 values were the highest in winter and lowest in summer, whereas monthly mean δ15N-NH3 values were the highest in January and lowest in June. The isotope mixing model results showed that agricultural sources account for 64.5 ± 13.5 % of year-round total NH3 emissions, while industrial and other sources contributed 27.4 and 8.1 %, respectively. However, the contribution of industrial sources was higher than that of agricultural sources in January. Our results indicated that the contribution of agricultural sources has decreased after the implementation of air pollution control policies in this region suggesting that NH3 abatement from agricultural sources is effective. However, further refinement of agricultural emission abatement measures will be required, accompanied by a greater focus on controlling winter non-agricultural sources.

为了筛选出水稻生产中应用效果更佳的硝化抑制剂,在太湖地区开展水稻季田间小区试验,尿素中分别添加化学合成硝化抑制剂2-氯-6-三氯甲基吡啶(CP)和3,4-二甲基吡唑磷酸盐(DMPP)以及生物硝化抑制剂对羟基苯丙酸甲酯(MHPP),探讨3种不同硝化抑制剂对水稻季N2O排放、NH3 挥发、水稻产量和氮肥利用率的影响.结果表明,与单施尿素处理相比,尿素添加3种硝化抑制剂能显著减少N2O排放总量,抑制效果表现为DMPP(31.71%)＞MHPP(30.40%)＞CP(27.83%),不同硝化抑制剂间减排效果无显著差异;添加硝化抑制剂均显著增加了NH3 挥发总量,促进作用表现为CP(58.7%)＞DMPP(40.3%)＞MHPP(25.3%),不同硝化抑制剂间差异显著;添加硝化抑制剂的增产幅度为 MHPP(4.9%)＞CP(3.3%)＞DMPP(1.1%),不同硝化抑制剂间无显著差异;氮肥表观利用率显著增加,表现为MHPP(15.7%)＞CP(13.8%)＞DMPP(10.9%),但不同硝化抑制剂间无显著差异;综合考虑活性气态氮损失量和水稻产量,3 种硝化抑制剂相比单施尿素均显著增加了单位产量活性气态氮排放强度,增加幅度表现为 CP(50.3%)＞DMPP(35.0%)＞MHPP(17.8%),CP显著高于DMPP和MHPP.综合比较,生物硝化抑制剂MHPP在水稻生产中增效减排的作用优于化学合成硝化抑制剂CP和DMPP,但在生产应用中要与其他NH3 挥发减排措施相结合,更好地发挥其增效减排潜力,推动农业绿色可持续发展.

本研究以太湖地区稻田为研究对象开展连续两年的田间试验,通过设置不施氮肥(CK)、常规施氮(CN)、减氮表施(RN)、减氮侧深施(RNS)和减氮穴施(RNP)5 种施氮处理,探究不同深施方式对稻田氨挥发与氮肥利用率的影响.结果表明,与表施处理(CN和RN)相比,RNS和RNP通过降低田面水NH4+-N浓度和pH分别减少30.95%～41.54%和66.71%～72.23%的氨挥发排放(P<0.05).相较于RN处理,RNP促进水稻根系生长并增加根区土壤有效氮含量,进而增加水稻产量(6.23%),提高氮肥利用率(50.15%),降低土壤氮盈余(63.92%)(P<0.05).与CN处理相比,RNS显著降低土壤氮盈余(29.20%)(P<0.05),但水稻吸氮量和氮肥利用率均未显著增加.相较于 RNS,RNP 进一步降低氨挥发损失(50.84%)和土壤氮盈余(51.07%),提高氮肥利用率(40.40%)(P<0.05).综上所述,RNP的农学和环境效益最高,但因穴施机械及肥料造粒技术等因素的限制,尚难应用于实际生产;而侧深施肥在我国水稻大规模集约化生产中效益较高且切实可行.

【Objectives】We studied the effects of urea fertilization methods on rice yield, nitrogen utilization efficiency, and the fate of nitrogen fertilizer in soil to propose economically and environmentally friendly N management measures. 【Methods】A paddy field experiment was conducted in the Taihu Lake region in 2019and 2020, and a 15 N-urea micro-plot experiment was installed in the same field plot in 2020. Urease inhibitor N-（nbutyl）thiophosphoric triamide（NBPT） and nitrification inhibitor methyl 3-（4-hydroxyphenyl） propionate（MHPP）were added at 1% of urea-N. We included six fertilizer treatments: no N application（CK）; broadcasted urea N at300 kg/hm~2（conventional fertilization, CN）; broadcasted urea N at 225 kg/hm~2（RNB）; 50% in deep and 50% in broadcasting of urea N at 225 kg/hm~2（RND）; broadcasted urea N at 225 kg/hm~2+NBPT+MHPP（RNB+DI）; 50%in deep and 50% in broadcasting of urea N at 225 kg/hm~2+NBPT+MHPP（RND+DI）. Broadcasted urea N was applied in three splits（4 : 3 : 3） as basal, at tillering and panicle initiation stages. Deep-placed nitrogen was applied in two splits（7 : 3） as basal, and at panicle initiation stage. Rice yield, N uptake, N utilization, absorptive capacity, soil residual and total 15 N loss were quantified.【Results】Compared with CN, RNB, RND, RNB+DI and RND+DI treatments recorded similar grain yield and straw biomass, except the lower straw biomass in RNB in 2020; However, all the four treatments achieved higher N use efficiency, agronomic efficiency and partial factor productivity of nitrogen fertilizer, and 15 N tracing result also proved the significant reduction in 15 N uptake and total N loss under the four treatments. Compared with RNB, RND enhanced apparent N recovery efficiency（NRE） and 15 N use efficiency by 20.4%–27.3% and 28.2%, and reduced 15 N loss by 34.6%（P＜0.05）. RNB+DI had no impact on NRE, but（P＜0.05） increased 15 N use efficiency by 11.6% and reduced 15 N loss rate by 13.1%.RND+DI increased rice yield by 2.6%–4.3%, NRE by 23.4%, 15 N use efficiency by 36.9%, and reduced 15 N loss by 45.0%. Compared with RND, RNB+DI had no impact on rice yield and NRE but reduced the 15 N loss rate. 【Conclusions】In the rice production of Taihu lake area, the measurement of reducing urea-N rate from 300 kg/hm~2 to 225 kg/hm~2, but increasing the basal fertilizer ratio from 40% to 70%, and changing total broadcasting to 50% by deep placement, will not decrease rice yield, but significantly increase nitrogen fertilizer use efficiency, decrease total N loss. Adding NBPT and MHPP in urea will further decrease the total N loss. We recommend that a higher proportion of urea should be allocated to the deep basal placement and a lower proportion to broadcasting, rather than adding N inhibitors, to increase rice yield and N use efficiency.

【Objectives】NH 3 volatilization and N 2 O emission from paddy fields were determined under different fertilization methods and urease/nitrification inhibitor addition,to optimize fertilization measures.【Methods】A two-year paddy field experiment was conducted in the Taihu Lake region.The urease inhibitor N-（n-butyl） thiophosphoric triamide（NBPT） and nitrification inhibitor methyl 3-（4-hydroxyphenyl） propionate（MHPP） were applied at 1% urea-N.The six treatments include no N application（CK）,broadcasted urea N at 300 kg/hm~2（conventional fertilization,CN）,broadcasted urea N at 225 kg/hm~2（RNB）,50% in deep urea N application at 225 kg/hm~2（RND）,broadcasted urea N application at 225 kg/hm~2+NBPT+MHPP（RNB+DI）,and 50% in deep urea N placement at 225 kg/hm~2+NBPT+MHPP（RND+DI）.The dynamic chamber technique was used to monitor NH 3 volatilization flux from the paddy field within two weeks after fertilization.The static chamber-gas chromatography method was used to monitor N 2 O emission flux from paddy field across the rice season.【Results】1) The NH 3 volatilization lasted for 7 days after fertilization.The total NH 3 volatilization after broadcasting basal and tillering fertilizer accounted for 86.63%–91.76% of the total NH 3 volatilization.The N 2 O emission flux peaks appeared after fertilization and halfway through aeration.2) Compared with the CN,RNB decreased total NH 3 volatilization and N 2 O emission by 29.69%–39.41% and 13.43%–23.37%,respectively.3) Compared with the broadcasted urea application（RNB）,deep placement of urea（RND） decreased total NH 3 volatilization and N 2 O emission by 53.50%–72.05% and 16.66%–23.43%,respectively（P＜0.05）.4) Compared with RNB,RNB+DI decreased total NH 3 volatilization and N 2 O emission by 9.57%–22.27% and 8.77%–15.67%.5) Compared with CN,RND+DI（P＜0.05） decreased total NH 3 volatilization and N 2 O emission by 76.89%–82.29% and 37.98%–48.71%.【Conclusions】NH 3 volatilization and N 2 O emission can be decreased by reducing the N application rate,N-fertilizer deep placement and adding inhibitors in urea,which had a better effect on NH 3 volatilization reduction.The combination of these optimized N fertilization measures can achieve optimum NH 3 and N 2 O emissions reduction effects.The comprehensive integration measure is feasible in practice and provides technical support for promoting rice production.

Meeting the sustainable development of agriculture is a challenge as the yield is stagnant and the quality is declining under the extensive fertilization method with excessive nitrogen (N) input. Therefore, an improved nitrogen (N) application method was essential for the simultaneous improvement of rice yield and quality. This study explored the effects of different fertilization methods (CK: no N input, RN: urea with three-split broadcasting with recommended N rates, RON: organic–inorganic fertilizer with two-split broadcasting, RONSA: Azolla incorporated with the side-deep placement of organic–inorganic fertilizer) on rice yield and quality, rice root characteristics, and N use efficiency (NUE) in a 2-year field experiment in the Taihu Lake region, China, and 15 N-labeled technique was used to investigate the fate of 15 N and protein synthesis in rice grains under different fertilization methods. Our results suggested that RONSA significantly increased rice yield, partial factor productivity of N input, and apparent N recovery efficiency versus RN, owing to the developed rice root system and enhanced N uptake in rice plants. Compared to RN, RONSA achieved higher eating and nutritional quality by reducing amylose content (by 18.02%) and increasing albumin (by 3.62%) and glutelin (by 9.70%) content. Furthermore, the markedly increased 15 N recovery efficiency and protein 15 N content indicated that RONSA markedly increased fertilizer N recovery and enhanced the uptake of fertilizer N to synthesize protein in rice grain. As an improved fertilization method, RONSA is promising to improve the eating and nutritional quality of rice while increasing rice yield and NUE. Investigating its effects on different rice cultivars and enhancing Azolla ’s resistance to adversity will help to promote the sustainable development of rice production in China.

Northeast and East China account for similar to 36% of the Chinese rice cultivation area, yet considerable spatial disparities in nitrogen use efficiency (NUE) exist between these regions. The underlying causes remain poorly understood. Herein, we conducted a case study in two sample sites from two regions, Wuchang and Changshu, using multi-scale evidence chains spanning macro- and micro- processes to identify the determinants of spatial NUE variability. Field studies showed higher NUE (partial factor productivity, PFP, and agronomic efficiency, AE) but lower ammonia volatilisation in Wuchang paddy soil. By separating edaphic factors from climatic conditions, soil replacement pot studies between Wuchang and Changshu revealed that both apparent (AE and recovery efficiency, RE) and N-15-traced NUE were higher, whereas N-15 fertilizer losses were lower in Wuchang-soil than Changshu-soil irrespective of site, suggesting soil type contributed to differences in soil N retention capacity and NUE of the soils. Process-scale results showed that greater rates of gross N mineralizsation (13-fold higher), gross nitrification (93% higher), and denitrification (52% higher) in Changshu-soil compared to Wuchang-soil corresponded to functional gene relative abundance, signifying larger reactive N losses and reduced soil N retention capacity. Microbial community analysis suggested that the differential N transformations were caused by differences in ammonia-oxidizing archaea (AOA) family nitrososphaeraceae and Nitrospira-like nitrite-oxidizing bacteria (NOB). This highlights the importance of specific efficiency-enhanced strategies tailored to the edaphic characteristics of cropping regions, such as increasing soil N retention capacity using enhanced-efficiency fertilizer in East China, while implementing conservation management strategies in Northeast China. Highlights: Field-scale studies revealed higher NUE and lower NH3 volatilisation in Wuchang site. Soil replacement pot studies showed higher NUE in Wuchang-soil regardless of sites. Process-scale results unravelled high N losses and low soil N retention in Changshu-soil. Varying NUE partially correlated with Nitrososphaeraceae AOA and Nitrospira-like NOB.

Silver nanoparticles (AgNPs) can enter soils via the application of sludge and pose risks to soil invertebrates. However, current knowledge regarding the toxicity of AgNPs at environmentally relevant concentration is insufficient, especially at the molecular level. Therefore, we examined the effects of low-level AgNPs (7.2 mg kg(-1), dry weight) on the bioaccumulation, pathology and metabolism of earthworms (Pheretima guillemi). After exposure for 28 d, earthworms were dissected into digestive system and the rest of the body to explore the response of different body parts to AgNPs. Ag concentration in the digestive system of exposed group (2.5 mg kg(-1), dry weight) was significantly higher than that of the control group (0.5 mg kg(-1), dry weight). AgNPs exposure had no significant effects on the survival and growth, but induced intestinal damage and metabolic interference to earthworms relative to the control. Metabolomics analysis showed that AgNPs exposure disturbed the glycerophospholipid metabolism, glutathione metabolism and energy metabolism in the digestive system and the energy metabolism in the rest of the body. AgNPs exposure also induced lipid peroxidation in the digestive system. The different metabolic responses between two body parts highlighted the importance of the uptake routes of Ag. These results provide a biochemical insight for the risk assessment of low-level AgNPs in terrestrial environment.

密闭室抽气法是稻田氨挥发的常用监测方法,但该方法在实施过程中仍存在一些问题,导致不同研究结果之间缺乏可比性,影响稻田氨排放的系统分析与评估.研究了换气频率、抽气时间段、是否串联洗气瓶、抽气室与洗气瓶规格等监测参数以及抽气与自然风对比对氨挥发量的影响.结果表明,氨挥发随换气频率的增加而增加,其增加速度分三个阶段,挥发量与换气次数的对数呈线性相关;尿素快速水解期与水解基本结束后的氨挥发日变化规律不同;直通型、球形多孔型洗气头分别较圆盘多孔型洗气头氨挥发量低25.6％和8.5％;抽气室内径越大,气相高度越低,氨挥发量越低;串联洗气瓶测定的氨挥发仅为单独洗气瓶的88.6％;抽气室内田面水蒸发量随抽气速率增加而增加,抽气与自然放置情况下氨挥发量相近时,后者田面水蒸发量大.建议密闭室抽气法监测稻田氨挥发采用直径15 cm的抽气室,配单独流量计,气相高度5～8 cm,抽气量15～20 L·min?1左右,无需串联洗气瓶,选择圆盘多孔型或直杆多孔型洗气瓶.