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Maize (Zea mays L.) fertilizer nitrogen (N) recovery efficiency (FNRE) shows regional differences in China, and is more strongly affected by soil properties than by climate. However, how soil factors regulate maize FNRE is poorly understood. Herein, 15N tracer pot experiments combined with absolute microbial quantification sequencing were conducted using eight soils covering the main maize cropping systems from northern to southern China. The aim was to elucidate which soil factors affect maize FNRE and identify their optimal range for maximizing FNRE while minimizing N loss. Our results show that soil pH, soil organic matter (SOM), and clay and sand contents were the key factors affecting maize biomass and FNRE across the eight tested soils. Maize biomass and FNRE had parabolic relationships with soil pH, SOM, clay, and sand contents, whereas N loss displayed the opposite trend. The highest maize biomass and FNRE and lowest fertilizer N loss were in the soils with pH of 6.50–6.62, SOM level of 35.25–46.90 g kg−1, clay content of 41.12 %–44.42 %, and sand content of 17.71 %–23.41 %. Under these soil conditions, maize growth and soil N retention capabilities exhibited a high degree of coordination. Bacterial communities differed significantly among the soils, sharing the same soil drivers as maize biomass and FNRE. The abundance of N cycling genes (nasA, narI, narJ, nrfA, and nrfB) involved in dissimilatory nitrate reduction to ammonium (DNRA) was positively correlated with FNRE and negatively correlated with fertilizer N loss, suggesting that DNRA may contribute to soil N retention and enhance FNRE by affecting substrates for nitrification and denitrification. Our study demonstrates that soil pH, SOM, and texture are three key factors driving FNRE variation in maize cropping systems across China, and high microbial-driven DNRA may account for maximum maize FNRE. These findings highlight the importance of tailored FNRE enhancement strategies based on soil characteristics.

The effects of nitrogen (N) deposition on forests largely depend on the ecosystem N status and the fates of deposited N. Boreal forests are typically N-limited ecosystems and are considered to be more efficient in retaining deposited N relative to temperate and tropical forests. As a primary disturbance in boreal forests, wildfires may alleviate N limitation in the burned ecosystem and increase mineralization, resulting in the altered outcomes of the N deposition. In order to explore the effects of a severe wildfire on the retention of deposited N, we investigated the fates of newly deposited N in burned and unburned boreal larch forests by applying 15NH4NO3 tracers to the forest floors. Results showed that total ecosystem retention for the deposited N was 60% in the forest recovering from a severe wildfire burned five years ago, significantly lower than in the unburned mature forest (89%). The difference was mainly attributed to the substantially lower retention in vegetation (8.3%) in the burned site than in the unburned forest (32.4%), as tracer recoveries in soil were similar (51.2 and 56.6%, respectively). Although most 15N tracer was immobilized in organic soil in both burned and unburned forests (33 and 47%, respectively), a noticeably higher amount of 15N was found in mineral soil in the burned forest (19%) than in the unburned forest (10%), suggesting mineral soil as a significant sink for N deposition in the burned forest. A higher total 15N retention in the unburned forest implies that more new N input may stimulate C sequestration and promote the productivity of the Eurasian boreal forest under the background of atmospheric N deposition. However, a considerable amount of deposited N may be lost from the disturbed boreal larch forest ecosystem after a severe wildfire. [ABSTRACT FROM AUTHOR]

Splitting nitrogen (N) application is beneficial for achieving higher grain yields and N use efficiency (NUE), but the responses of N utilization efficiency of different maize cultivars to top-dressing N fertilizer rates are still unclear. This study investigated the effects of fertilization managements on N uptake and utilization derived from topdressing fertilizers of maize hybrids (Ludan981 and Denghai605) with contrasting NUEs. The N fate derived from topdressing fertilizer was determined using the 15N tracing method. Grain yields, dry matter and N accumulation of both maize hybrids were significantly increased under low N levels but decreased under high N levels. Under N-deficient and excess conditions, Denghai605 had higher NUE than Ludan981. The N rates of topdressing significantly affected N uptake and utilization, but no difference was detected between two maize hybrids, and excessive N use led to higher rates of N loss and residual in soil. The N metabolism enzyme activities did not differ between the two maize hybrids. Our findings suggest optimized N management strategies by adjusting topdressing N application rate and timing are necessary to increase NUE and to minimize environmental costs in maize cropping system. [ABSTRACT FROM AUTHOR]

● Excessive application of N fertilizers in orchards and vegetable fields (OVFs) in China is particularly common. ● Long-term excessive application of N fertilizers has made OVFs hotspots for N surplus and loss in China. ● Nitrate accumulation in the soil profile is the main fate of N fertilizers in OVF systems. ● Reducing the N surplus is the most effective way to reduce N loss and increase NUE. China is the largest producer and consumer of fruits and vegetables in the world. Although the annual planting areas of orchards and vegetable fields (OVF) account for 20% of total croplands, they consume more than 30% of the mineral nitrogen fertilizers in China and have become hotspots of reactive N emissions. Excess N fertilization has not only reduced the N use efficiency (NUE) and quality of grown fruits and vegetables but has also led to soil acidification, biodiversity loss and climate change. Studies using 15N labeling analysis showed that the recovery rate of N fertilizer in OVFs was only 16.6%, and a high proportion of fertilizer N resided in soils (48.3%) or was lost to the environment (35.1%). Nitrate accumulation in the soil of OVFs is the main fate of N fertilizer in northern China, which threatens groundwater quality, while leaching and denitrification are the important N fates of N fertilizer in southern China. Therefore, taking different measures to reduce N loss and increase NUE based on the main pathways of N loss in the various regions is urgent, including rational N fertilization, substituting mineral N fertilizers with organic fertilizers, fertigation, and adding mineral N fertilizers with urease inhibitors and nitrification inhibitors.

A large amount of nitrogen fertilizer is applied in maize planting in Northeast China, but the recovery rate is low, causing a series of water and soil environmental problems in farmland areas. Thus, based on isotope tracing technology and combining a field plot test with an in situ microzone test, we carried out an experiment under reduced nitrogen fertilizer conditions. Five different nitrogen application levels were set: conventional nitrogen application (N1: 250 kg ha−1), 10%-reduced nitrogen fertilizer (N-10: 225 kg ha−1), 20%-reduced nitrogen fertilizer (N-20: 200 kg ha−1), 30%-reduced nitrogen fertilizer (N-30: 175 kg ha−1), and nitrogen-free (N0: 0 kg ha−1) treatments. Yield, nitrogen accumulation in maize and nitrogen fertilizer fates were studied. The results showed that reducing nitrogen application rates improved the recovery rates of basal fertilizer and topdressing. Specifically, the recovery rate of basal fertilizer was 19.81–26.20%, and the recovery rate of topdressing was 40.24–47.71%. The loss rate of basal fertilizer was 19.96–39.18%, and nitrogen reduction decreased the loss rate of basal fertilizer. The loss rate of topdressing ranged from 36.46 to 41.76%. The residual rates of basal fertilizer and topdressing in the 0–100 cm soil layer were 41.01–53.84% and 12.22–22.30%, respectively. As the nitrogen application rate decreased, corn yield and nitrogen accumulation in maize decreased. Reductions of 20% and 30% in nitrogen fertilizer had a negative influence on plant nitrogen accumulation. This experiment revealed the effect of reducing nitrogen fertilizer application rates on the fate of nitrogen fertilizer, maize yield and nitrogen accumulation in Northeast China. In Northeast China, reducing the nitrogen fertilizer application rate could increase the nitrogen fertilizer recovery rate and reduce nitrogen fertilizer loss amounts and the risk of environmental pollution, but reduce maize yield. [ABSTRACT FROM AUTHOR]

The Yangtze River Basin (YRB) crosses three economic zones and major agricultural regions of eastern, central, and western China. Increasing non-point source pollution, caused by excessive nitrogen (N) inputs to farms, is one of the main causes of water contamination in the YRB. To improve N fertilizer use efficiency, we conducted a field experiment using 15N-labeled urea at three sites located in upstream, midstream, and downstream regions of the YRB to evaluate the impacts of improved fertilizer management on crop yield, fertilizer N recovery, and losses in three crop rotations: rice–wheat (RW), rice–vegetable (RV) [tuber mustard at Jiangjin (Chongqing), cabbage at Shayang (Hubei), and savoy cabbage at Rugao (Jiangsu)] and maize–wheat (MW). Applying only 50% of the traditional application of N and P fertilizer maintained the wheat yield at Jiangjin and Shayang and savoy cabbage yield at Rugao. However, it caused a 27% reduction of the wheat yield at Rugao. The 15N recovery showed that 27% of the fertilizer N was retained in the soil and that 25% less fertilizer N was lost to the environment compared to the traditional fertilizer application. Improved fertilizer management would reduce the environmental cost of farming in the YRB, but with some consequences to winter crop yields.

Purpose: NH4+ and NO3− are the two main inorganic N forms available for plant growth, and NO3− is the preferred N source of maize (Zea mays L.) grown in acid soils. However, the mechanisms for this preference and its contribution to fertilizer N recovery efficiency (FNRE) remained unclear. Materials and methods: In this 30-day pot experiment, acid soil (pH 4.54; base saturation, 27%) with or without maize plants was supplied with 15N-labeled NH4Cl (20.12 atom % excess), NaNO3 (30.15 atom % excess), or urea (20.10 atom % excess) at the rate of 200 mg N kg−1 without or with liming (1.2 g CaCO3 kg−1). Results and discussion: Without liming, maize biomass and FNRE were higher under NO3− or urea than under NH4+. Lime increased the maize biomass and FNRE by 421–835% under NH4+ and by 30–112% under NO3− or urea. Without lime, the maize shoot Al concentration was much lower under urea or NO3− than under NH4+, because NH4+ decreased soil pH by 0.35 units and increased soil exchangeable Al concentration by 4–11%. Lime increased soil pH by 0.1–0.3 units and decreased soil exchangeable Al concentration by 25–57%. Among various treatments, the biomass of maize plants was negatively correlated with soil exchangeable Al concentration. Conclusions: The preference of maize plants for NO3− improves the FNRE of maize in acid soil partially due to alleviated Al toxicity as a result of soil pH increase. [ABSTRACT FROM AUTHOR]

A large amount of nitrogen fertilizer is applied in maize planting in Northeast China, but the recovery rate is low, causing a series of water and soil environmental problems in farmland areas. Thus, based on isotope tracing technology and combining a field plot test with an in situ microzone test, we carried out an experiment under reduced nitrogen fertilizer conditions. Five different nitrogen application levels were set: conventional nitrogen application (N1: 250 kg ha−1), 10%-reduced nitrogen fertilizer (N-10: 225 kg ha−1), 20%-reduced nitrogen fertilizer (N-20: 200 kg ha−1), 30%-reduced nitrogen fertilizer (N-30: 175 kg ha−1), and nitrogen-free (N0: 0 kg ha−1) treatments. Yield, nitrogen accumulation in maize and nitrogen fertilizer fates were studied. The results showed that reducing nitrogen application rates improved the recovery rates of basal fertilizer and topdressing. Specifically, the recovery rate of basal fertilizer was 19.81–26.20%, and the recovery rate of topdressing was 40.24–47.71%. The loss rate of basal fertilizer was 19.96–39.18%, and nitrogen reduction decreased the loss rate of basal fertilizer. The loss rate of topdressing ranged from 36.46 to 41.76%. The residual rates of basal fertilizer and topdressing in the 0–100 cm soil layer were 41.01–53.84% and 12.22–22.30%, respectively. As the nitrogen application rate decreased, corn yield and nitrogen accumulation in maize decreased. Reductions of 20% and 30% in nitrogen fertilizer had a negative influence on plant nitrogen accumulation. This experiment revealed the effect of reducing nitrogen fertilizer application rates on the fate of nitrogen fertilizer, maize yield and nitrogen accumulation in Northeast China. In Northeast China, reducing the nitrogen fertilizer application rate could increase the nitrogen fertilizer recovery rate and reduce nitrogen fertilizer loss amounts and the risk of environmental pollution, but reduce maize yield.

The aim of this study was to track the fate of nitrogen derived from fertilizer (Ndff) after fertilization. A field in situ experiment covering an entire growing season by using 15N-doubly-labelled urea as fertilizer was conducted at a paddy field inSanjiang Plain in northeastern China. Results showed that approximately 70% of total nitrogen (TN) output load was from Ndff, and the lateral seepage contributed ~47% and ~40% of TN and Ndff output loads, and the rest of the TN and Ndff output loads were derived from runoff and artificial drainage. The Ndff contents in paddy root, stalk, foliage and kernel increased with increasing fertilization dosages -- from the tillering stage to mature stage. Ndff accumulated in the root, stalk and foliage during tillering and the milk stage migrated to the kernel in the mature stage. Most of the residual Ndff in soil was distributed in the top layer (0-10 cm). Crop utilization and gaseous loss were the main fates of Ndff in the paddy field. The proportion of crop utilization with an average value of ---37% increased from 30.29% to 43.52% with increasing fertilization dosages, while the proportion of gaseous loss decreased from 49.61% to 32.74% with increasing fertilization dosages. 180 kg N hm-2 was the optimum fertilization dosage for crop utilization rate and non-point source pollution control in the rice-growing area of Sanjiang Plain. [ABSTRACT FROM AUTHOR]

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The influence of temperature (180–260 °C) on the fate of nitrogen during hydrothermal carbonization (HTC) of food waste (FW) was assessed. The distribution and evolution of nitrogen in aqueous products and bio-oil, as well as hydrochar, were conducted. Results suggested that elevated temperature enhanced the deamination and the highest ammonium concentration (929.75 mg/L) was acquired at 260 °C. At temperatures above 220 °C, the total N in the hydrochar became stable, whereas the mass percentage of N increased. Amines and heterocyclic-N compounds from protein cracking and Maillard reactions were identified as the main nitrogen-containing compounds in the bio-oil. As to the hydrochar, increasing temperature resulted in condensed nitrogen-containing aromatic heterocycles (e.g. pyridine-N and quaternary-N). In particular, remarkable Maillard reactions at 180 °C and the highest temperature at 260 °C enhanced nitrogen incorporation (i.e. quaternary-N) into hydrochar. [ABSTRACT FROM AUTHOR]

Increasing atmospheric reactive nitrogen (N) deposition due to human activities could change N cycling in terrestrial ecosystems. However, the differences between the fates of deposited [ABSTRACT FROM AUTHOR]

The impact of atmospheric nitrogen deposition on forest ecosystems depends in large part on its fate. Past tracer studies show that litter and soils dominate the short-term fate of added 15N, yet few have examined its longer term dynamics or differences among forest types. This study examined the fate of a 15N- [ABSTRACT FROM AUTHOR]

Ecological remediation is one of the most practical methods for removing nutrients from river ecosystems. In this study, transformation and fate of nitrate and ammonium among four different ecological restoration treatments were investigated by stable N isotope pairing technique combined with quantitative polymerase chain reaction and high-throughput sequencing technology. The results of N mass-balance model showed that there were three ways to the fate of nitrogen: precipitated in the sediment, absorbed by Elodea nuttallii ( E. nuttallii), and consumed by microbial processes (denitrification and anaerobic ammonium oxidation (anammox)). The results shown that the storage of NH in sediments was about 1.5 times as much as that of NO . And much more NH was assimilated by E. nuttallii, about 2 times as much as NO . Contrarily, the rate of microbial consuming NO was higher than converting NH . As for the group with NO added, 29.61, 45.26, 30.66, and 51.95 % were accounted for N-labeled gas emission. The proportions of NH loss as N-labeled gas were 16.06, 28.86, 16.93, and 33.09 % in four different treatments, respectively. Denitrification and anammox were the bacterial primary processes in N and NO production. The abundances of denitrifying and anammox functional genes were relatively higher in the treatment with E. nuttallii-immobilized nitrogen cycling bacteria (E-INCB) assemblage technology applied. Besides, microbial diversity increased in the treatment with E. nuttallii and INCB added. The NO removal rates were 35.27, 49.42, 50.02, and 65.46 % in four different treatments. And the removal rates of NH were 24, 34.38, 48.84, and 57.74 % in treatments A, B, C, and D, respectively. The results indicated that E-INCB assemblage technology could significantly promote the nitrogen cycling and improve nitrogen removal efficiency. [ABSTRACT FROM AUTHOR]

Sequential anaerobic–aerobic digestion has been demonstrated to be effective for enhanced sludge stabilization, in terms of increased solid reduction and improvement of sludge dewaterability. In this study, we propose a modified version of the sequential anaerobic–aerobic digestion process by operating the aerobic step under mesophilic conditions (T = 37 °C), in order to improve the aerobic degradation kinetics of soluble and particulate chemical oxygen demand (COD). Process performance has been assessed in terms of “classical parameters” such as volatile solids (VS) removal, biogas production, COD removal, nitrogen species, and polysaccharide and protein fate. The aerobic step was operated under intermittent aeration to achieve nitrogen removal. Aerobic mesophilic conditions consistently increased VS removal, providing 32% additional removal vs. 20% at 20 °C. Similar results were obtained for nitrogen removal, increasing from 64% up to 99% at the higher temperature. Improved sludge dewaterability was also observed with a capillary suction time decrease of ~ 50% during the mesophilic aerobic step. This finding may be attributable to the decreased protein content in the aerobic digested sludge. The post-aerobic digestion exerted a positive effect on the reduction of microbial indicators while no consistent improvement of hygienization related to the increased temperature was observed. The techno-economic analysis of the proposed digestion layout showed a net cost saving for sludge disposal estimated in the range of 28–35% in comparison to the single–phase anaerobic digestion. [ABSTRACT FROM AUTHOR]

To investigate the fate of urea nitrogen (N) applied to vegetable fields, three N rates, N0 (0 kg N/ha), N1(225 or 240 kg N/ha) and N2 (450 or 480 kg N/ha) were applied to a rotation system. Nitrogen fertilizer recovery (NFR), N residue in soil, and N losses were measured in situ. Higher N application rates resulted in lower NFR, and increased N residues in soil and losses. The NFR, Chinese cabbage, and eggplant were different in the N1 and N2 groups ( P < 0.01). The ratios of N fertilizer residue at 0-60 cm deep ranged from 30.2 to 41.1 % (N1), and 33.1 to 57.7 % (N2). The N loss ratios were only 6.6 % (N1) and 11.9 % (N2), because of the lower precipitation rates and temperatures characteristic of its growing season; meanwhile, N losses were 31.1 and 37.4 % in cayenne pepper, and 24.1 and 29.2 % in eggplants in the N1 and N2 treatments, respectively. The main pathways of N loss were leaching, followed by gaseous losses; these were major pathways of N loss in seasons with lower precipitation rates. NH volatilization was correlated with soil temperature ( P < 0.01), and NO emissions were correlated with soil moisture in the N1 treatment and with soil NH-N concentration in the N2 treatment ( P < 0.01). Denitrification rates were correlated with soil moisture in the N0 and N1 treatments, and with NO-N content in the N2 treatment ( P < 0.01). Finally, loss due to runoff was correlated with precipitation ( P < 0.01). [ABSTRACT FROM AUTHOR]

Nitrogen reduction combined with organic fertilizer is of considerable significance for the sustainable development of agriculture. A pot experiment using nitrogen reduction combined with organic fertilizer was conducted to explore the effects of different treatments on matter accumulation, physiological resistance, and fertilizer nitrogen fate in banana seedlings. Compared with conventional fertilization, a 20% reduction of nitrogen did not affect the dry weight, chlorophyll content, physiological resistance, and fertilizer utilization rate of banana seedlings, but significantly reduced the nitrogen leaching loss and increased the nitrogen soil residue. Compared with conventional fertilization, organic nitrogen substituting 20% or 30% of the nitrogen reduced by 20% significantly promoted dry matter accumulation and physiological resistance. Organic nitrogen substituting 30% of the 20% reduction of nitrogen increased the dry matter of the whole plant by 24.94%, the nitrogen uptake in the root by 30.87%, the chlorophyll content by 6.05%, the soluble sugar content by 16.88%, Peroxidase (POD) activity by 26.35%, Catalase (CAT) activity by 27.48%, and Super Oxide Dismutase (SOD) activity by 22.97%. Compared with conventional fertilization, all organic substitution treatments significantly reduced fertilizer nitrogen leaching loss, apparent loss, and increased nitrogen soil residue. Compared with the 20% reduction of nitrogen, organic nitrogen substituting 30% of the 20% reduction of nitrogen significantly increased nitrogen utilization by 16.34% and soil residue rate by 13.26%, and reduced nitrogen leaching loss by 35.46%. The results of the present study revealed that a 20% reduction of nitrogen fertilizer with a 30% organic substitution application promoted matter accumulation, enhanced the physiological resistance of banana seedlings, increased the utilization and residue of nitrogen fertilizer, and reduced nitrogen pollution. • Nitrogen reduction with organic fertilizer increased nitrogen availability. • Nitrogen reduction with organic fertilizer promoted matter accumulation of banana. • Nitrogen reduction with organic fertilizer improved the physiological resistance. • Nitrogen reduction with organic fertilizer reduced nitrogen loss and pollution. [ABSTRACT FROM AUTHOR]

Sequential anaerobic-aerobic digestion has been demonstrated as a promising alternative for enhanced sludge stabilization. In this paper, a feasibility study of the sequential digestion applied to real waste activated sludge (WAS) and mixed sludge is presented. Process performance is evaluated in terms of total solid (TS) and volatile solid (VS) removal, biogas production, and dewaterability trend in the anaerobic and double-stage digested sludge. In the proposed digestion lay out, the aerobic stage was operated with intermittent aeration to reduce the nitrogen load recycled to the wastewater treatment plant (WWTP). Experimental results showed a very good performance of the sequential digestion process for both waste and mixed sludge, even if, given its better digestibility, higher efficiencies are observed for mixed sludge. VS removal efficiencies in the anaerobic stage were 48 and 50 % for waste and mixed sludge, respectively, while a significant additional improvement of the VS removal of 25 % for WAS and 45 % for mixed sludge has been obtained in the aerobic stage. The post-aerobic stage, operated with intermittent aeration, was also efficient in nitrogen removal, providing a significant decrease of the nitrogen content in the supernatant: nitrification efficiencies of 90 and 97 % and denitrification efficiencies of 62 and 70 % have been obtained for secondary and mixed sludges, respectively. A positive effect due to the aerobic stage was also observed on the sludge dewaterability in both cases. Biogas production, expressed as Nm/(kgVS), was 0.54 for waste and 0.82 for mixed sludge and is in the range of values reported in the literature in spite of the low anaerobic sludge retention time of 15 days. [ABSTRACT FROM AUTHOR]

Field undisturbed tension-free monolith lysimeters and 15N-labeled urea were used to investigate the fate of fertilizer nitrogen in paddy soil in the Taihu Lake region under a summer rice-winter wheat rotation system. We determined nitrogen recovered by rice and wheat, N remained in soil, and the losses of reactive N (i.e., NH3, N2O, NO3 −, organic N and NH4 +) to the environment. Quantitative allocation of nitrogen fate varied for the rice and wheat growing seasons. At the conventional application rate of 550 kg N ha−1 y−1 (250 kg N ha−1 for wheat and 300 kg N ha−1 for rice), nitrogen recovery of wheat and rice were 49% and 41%, respectively. The retention of fertilizer N in soil at harvest accounted for 29% in the wheat season and for 22% in the rice season. N losses through NH3 volatilization from flooded rice paddy was 12%, far greater than that in the wheat season (less than 1%), while N leaching and runoff comprised only 0.3% in the rice season and 5% in the wheat season. Direct N2O emission was 0.12% for the rice season and 0.14% for the wheat season. The results also showed that some dissolved organic N (DON) were leached in both crop seasons. For the wheat season, DON contributed 40–72% to the N- leaching, in the rice season leached DON was 64–77% of the total N leaching. With increasing fertilizer application rate, NH3 volatilization in the rice season increased proportionally more than the fertilizer increase, N leaching in the wheat season was proportional to the increase of fertilizer rate, while N2O emission increased less in proportion than fertilizer increase both in the rice season and wheat season. [ABSTRACT FROM AUTHOR]

Nitrogen management measures (NMMs) such as the application of urease inhibitors (UIs), synthetic nitrification inhibitors (SNIs), and biochar (BC) are commonly used in mitigating nitrogen (N) loss and increasing fertilizer recovery efficiency (FRE) in agriculture. Calcareous soil under rice cropping is characterized by high nitrification potential, N loss risk, and low FRE. Application of SNIs may stimulate NH 3 volatilization in high pH soils and the effects of SNIs on FRE are not always positive. BNIs have many advantages over SNIs. Whether combined application of BNI, UI, and BC that can result in a synergistic effect of improving FRE and decreasing N loss in a calcareous soil under rice cropping worth investigating. In this study, we conducted pot experiments to investigate the effects of single and co-application of BNI (methyl 3-(4-hydroxyphenyl) propionate or MHPP, 500 mg kg−1 soil), UI (N-(n -butyl), thiophosphoric triamide or NBPT, 2% of urea-N), or BC (wheat straw, 0.5% (w/w)) with chemical fertilizer on NH 3 volatilization, N 2 O emission, N leaching, crop N uptake, and FRE in a calcareous soil under rice cropping. Our results demonstrated that those NMMs could mitigate NH 3 volatilization by 12.5%–26.5%, N 2 O emission by 62.7%–73.5%, and N leaching loss by 17.5%–49.0%. However, BNI might have a risk of increasing NH 3 (5.98%) volatilization loss. Among those NMMs, double inhibitors (BNI plus UI) yielded a synergistic effect that could mitigate N loss to the maximum extent and effectively improve FRE by 25.4%. The mechanisms of the above effects could be partly ascribed to the niche differentiation between the abundance of AOA and AOB and the changed community structure of AOB, which could further influence nitrification and N fate. Our results demonstrated that co-application of BNI and UI with urea is an effective strategy in reducing N loss and improving FRE in a calcareous soil under rice cropping. • UI, BNI and BC could mitigate NH3 volatilization, N2O emission and N leaching. • BNI increased NH3 volatilization by 5.98% in calcareous soil under rice cropping. • Double inhibitors improve fertilizer recovery efficiency by 25.4%. • UI, BNI and BC lead to niche differentiation between AOA and AOB. • BNI, UI and BC changed the community structure mainly of AOB. [ABSTRACT FROM AUTHOR]

Feather mosses and associated cyanobacteria serve as an important source of nitrogen (N) in boreal forests; however, few studies have effectively traced the N 2 fixation in-situ for more than one year. The purpose of this study was to assess the long-term fate of N 2 fixed in feather moss carpets in boreal forests of northern Sweden. We conducted a seven-year 15N 2(g) labelling and tracing experiment in a boreal forest with a moss bottom layer dominated by Pleurozium schreberi Brid (Mitt). Mesocosms of forest floor with and without mosses present were exposed to a 10% 15N 2(g) atmosphere for five days after which samples of moss, shrub, pine seedling and O horizon were taken at varied intervals and analysed for δ15N. Plots were split and burned in year seven to assess the effect of fire on liberating moss N for uptake by Scots pine (Pinus sylvestris L.) seedlings. Feather mosses treated with 15N 2(g) were highly enriched in 15N one month after labelling which subsequently declined after seven years to 13% of the original 15N enrichment in green tissue. No measurable 15N enrichment was observed in shrubs or the O horizon in the presence of labelled mosses until greater than five years after the labelling experiment. Fire can liberate moss N, but we did not observe a direct effect of fire on N uptake by pine seedlings. This long-term study indicates that N 2 fixed by cyanobacteria in feather moss carpets is conserved in moss tissue for extended periods and slowly transferred to the forest soil O horizon as moss tissue decomposes suggesting that moss N 2 fixation is most important as an ecosystem N source at long time scales. [ABSTRACT FROM AUTHOR]

Abstract: In intensive livestock production areas, land application remains the traditional management of manure and slurries for nutrient recycling. For sustainable agriculture there is fear, however, that this practice may have detrimental effects, particularly on the depletion of Soil Organic Matter associated with pig slurry applications. We investigated the long-term fate of nitrogen in a reconstituted soil having received high doses of pig slurry during 5 years (1991–1995). After 5 years of intensive application rates (nearly 1000m3 yr−1), the N and C content of the soil profile (0–20cm) had increased by about 60% and 50%, respectively. These results confirm previous findings although it seems that the particularly high rates of application may explain, in part, the relatively important N incorporation in soil. Pig slurry applications ceased in 1995 and nitrogen content in soil and drainage water have been monitored. Apparent mineralization rates were calculated from the decrease in N content of the soil. This analysis indicated that more than 50% of the added N stored in the soil at the end of the applications would eventually be mineralized, leaving nearly 50% of the stored N to be immobilized in the soil. These results are the first published of their kinds, as most reports never examine the fate of applied pig slurry N after halting applications. In addition the few reports on long-term experiments suggest that Soil Organic Matter following pig slurry applications may be unstable. Our analysis tends to show the contrary. However, this conclusion must be tempered because data on nitrate leachate patterns suggest that soil management such as ploughing and sowing may actually trigger mineralization that could eventually deplete nitrogen stored following applications. [Copyright &y& Elsevier]

Abstract: For 40 years, aerobic thermophilic (AT) processes have been presented as a possible way of treating liquid manure, especially swine wastes. If they are well designed, bioreactors can be self-heating and a temperature up to 75 °C (but preferably in the 55–65 °C range) can be reached. Claimed benefits are the efficient destruction of pathogens, the simplicity of the process, its robustness, a higher reaction rate (and consequently smaller bioreactors), the conservation of nitrogen and the possibility of heat recovery. However, there are very few examples of implementation of AT technologies for this particular application. The aim of this review is to present the knowledge that has been acquired over the last 40 years through experimentations of AT processes with livestock wastes. [Copyright &y& Elsevier]

Elevated inputs of reactive nitrogen (Nr) have large and often detrimental effects on the environment and the magnitude and type of effects depend on the fate of Nr, such as water (NO 3 −) and air (N 2 O) pollution. Research has shown that soils are the primary sink of Nr in temperate forest ecosystems. Redox conditions, in conjunction with soil composition, stand to have an important but poorly constrained impact on the fate of this reactive N. In this study, we used tracer-level additions to contrast the fate of 15N–NO 3 - in organic (Oa) and in iron oxide-rich mineral (B) horizons under oxic and suboxic conditions. We performed stirred-jar laboratory incubations (up to 26 days) using soils from an acidic mixed-hardwood forest. We followed the fate of the tracer N into soil and solution pools (dissolved organic matter, NO 3 −, and NH 4 +), and also monitored solution concentrations of redox-sensitive species (NO 2 −, Fe2+, Fe3+, Mn). At the end of the incubations, ~3–7 times more tracer was recovered in soil material from the highly organic Oa horizon (57 ± 3% for oxic conditions and 73 ± 3% for suboxic) than in soil material from the organic-poor mineral B horizon (20 ± 5% for oxic, and 9 ± 2% for suboxic). For the B horizon, some 15N–NO 3 - remained in solution (29 ± 13%) under oxic conditions, while none remained under suboxic conditions (0.2 ± 0.02%); the main fate of 15N–NO 3 - went unrecovered, presumably due to gaseous losses, with more lost under suboxic (86 ± 3%) than oxic (47 ± 7%) conditions. Apparent gaseous losses were substantial in the Oa horizons as well, amounting to 35 ± 3% (oxic) and 12 ± 4% (suboxic) of tracer additions. Transformation rates of 15N–NO 3 - were greater under suboxic conditions for both horizon soil materials. Under both redox conditions retention was reaction rate limited in Oa horizon material and capacity limited in B horizon material. Our results indicate that in these acidic soils organic matter (OM) drives retention of nitrate in soil under both oxic and suboxic conditions, likely also accompanied by microbial denitrification; while lack of OM in iron oxide-rich mineral soils leaves nitrate available for other fates, with especially large gaseous loss in suboxic conditions. Mechanistically, it is likely that reduction of NO 3 − to NO 2 − is largely biotically driven, while subsequent reactions of NO 2 − are competitive between retention (nitrosation and microbial immobilization) and gasification (denitrification, chemodenitrification, self-decomposition) reactions. Both soil characteristics and redox conditions are critical determinants of NO 3 − fate in temperate forest ecosystems. [Display omitted] • Retention in soil dominated tracer fate in the organic-rich (Oa) horizon. • Losses, presumably to N gases, dominated tracer fate in the Fe-rich (B) horizon. • Suboxic conditions increased tracer N transformation rates in both soil horizons. • Tracer retention limited by reaction rate in Oa horizon and capacity limited in B. • Soil characteristics affect thermodynamic favorability of abiotic N reactions. [ABSTRACT FROM AUTHOR]

To sustain and maximize agricultural production in order to supply the nutritional needs of a continually growing world population, agricultural systems will need nitrogen (N) inputs. In its inert form as elemental dinitrogen (N2) gas in the atmosphere (78%), nitrogen does not impact environmental quality. But the extensive use of N in agricultural systems and the associated transformations of N into various ions or gaseous forms contribute to leaks from the N cycle. These N losses may contribute to the degradation of water, air, and soil in many regions of the world. When N is in its nitrate (NO3-) form, it is one of the most mobile ions in agricultural systems, and NO3- leaching is a primary source of the contamination in drinking water. Soil erosion that transports soil particles and N also contributes to surface water contamination. The gaseous transport of ammonia (NH3) from manures and the denitrification of NO3- and nitrite (NO2-) ions and their transformation into gaseous forms of N such as nitrous oxide (N2O) and nitric oxide (NO) can contribute to air quality and greenhouse warming impacts. Since N inputs are necessary for maintaining the viability of intensive agricultural systems, we must understand how management impacts the transformations, transport, and fate of N. The discussion of the transport and fate of N through agricultural systems must take into account the N cycle. Mitigation strategies that reduce the primary and secondary flows of N through the environment and that benefit farming and livestock operations must be developed. [ABSTRACT FROM AUTHOR]