By identifying the main sources of nitrate (NO3−) can obtain useful information to support the management of NO3− pollution, particularly in subtropical catchments with shallow drinking water wells. This study used water chemistry and dual stable isotopes δ15N and δ18O methods to assess seasonal and spatial variations of NO3− in precipitation, surface water, and groundwater in an agricultural and forest subtropical catchment in Jiangxi Province, China. The maximum concentrations of nitrate-nitrogen (NO3−-N) and ammonium-nitrogen (NH4+-N) were 10.4 and 10.8 mg L−1in samples collected from 221 rainfall events from 2011 to 2013. About 4.4% and 12.3% NH4+-N concentrations of surface water and groundwater exceeded the thresholds of 1.0 and 0.2 mg L−1. The NO3−-N concentrations in surface water were closely correlated with NH4+-N concentrations in surface water and groundwater (r = −0.71 and r = −0.71, P < 0.05). The concentrations of NH4+-N and NO3−-N were significantly higher in a fishery pond and nearby drinking wells than in other monitoring points. Annual exports of NO3−-N and NH4+-N were 4.06 × 104 and 8.14 × 103 kg yr−1, respectively and NO3−-N is the main form of N loss. The δ15N values ranged from 0‰ to 20‰ in surface water and groundwater, and the δ18O values ranged from 0‰ to 15‰ and 1‰–13‰, respectively. Dual stable isotope natural abundance distribution and water chemistry [NO3−]/[Cl−] molar ratio information suggested that manure and sewage and soil N were the main sources of NO3− in surface water and manure and sewage in groundwater in summer and winter. In spring, water occurred denitrification and ammonium fertilizer, manure and sewage were the main sources of NO3− in surface water and groundwater which sampling points were closer residential area and fish ponds than paddy field and local farmers used more Manure. Manure applications should be reasonable around drinking water wells to protect the drinking water quality.

Feammox is a newly discovered and important anaerobic nitrogen (N) loss pathway, and its variation and role in removing N following the application of N fertilizer and its migration from paddies to other land use types and from surface soils to deep soils have not been thoroughly elucidated to date. In this study, field sampling and slurry incubation experiments were performed to evaluate the Feammox rate between different land use types (paddy, irrigation ditch, riparian zone and lake, 0–10 cm) and different paddy soil depths (0–70 cm) in a wheat-rice rotation area in China. Based on a ¹⁵N-labelled isotope-tracing technique and analysis of microbial communities, it was estimated that the potential Feammox rate ranged from 0.031 to 0.42 mg N kg⁻¹ d⁻¹ in this area. In the soil profile of the paddy, the depth of 20–30 cm was the active region of Feammox, with a value of 0.37 ± 0.057 mg N kg⁻¹ d⁻¹. Compared with the surface soil (0–10 cm) of the paddy (0.18 ± 0.031 mg N kg⁻¹ d⁻¹), the potential Feammox rate of the irrigation ditch soil was not significantly different, but that of the lake riparian soil and lake sediment were decreased by 27.27% and 32.11%, respectively (p < 0.01). Fe(III) content was the best predictor of the Feammox rate and explained the variation of the Feammox rate by 36.00% in the surface soil. At the genus level, the paddy soil at a depth of 20–30 cm had the greatest abundance of the genera in which the Fe reduction bacteria were distributed; and where Bacillus, Geobacter and Anaeromyxobacter had higher proportions. It was estimated that the potential N loss by Feammox was in the range of 7.36 (the lake) ∼43.35 (the paddy) kg N ha⁻¹ year⁻¹ in the surface soil of this area. Considering denitrification and the Feammox rate as a whole, we found that denitrification remained to be the main contributor to N loss in the surface soil (94.72–96.89% of N loss), although Feammox dominated N loss in the deep soil (below 0–10 cm).

We studied the short- and medium-term effects of experimental nitrogen fertilization (3 and 15 months after the treatment) on the arthropods of Calluna vulgaris heathlands in NW Spain. Three heathland sites were selected with two permanent plots per site: control and fertilized. Ammonium nitrate fertilizer (56 kg N ha-1 yr-1) was applied monthly and insects were caught using pitfall traps. We found mainly species-level responses to nitrogen addition. Seven species (e.g. Lochmaea suturalis) showed a consistent trend (benefited or harmed) in both periods and were proposed as possible reliable indicators of the effects of nitrogen deposition in these ecosystems. We also found variable arthropod trophic-group responses: (a) herbivores (leaf beetles, true bugs) increased in abundance on a short-term scale; (b) predators (carabid beetles, true bugs) showed opposite and less clear responses in both periods. Further long-term studies are needed to determine the mechanisms underlying the observed arthropod responses. We observed consistent species-level and variable trophic-group responses to nitrogen addition in one of the southern-most locations for Calluna vulgaris heathlands within Europe.

Ammonia fluxes from application of anaerobically-digested slurry (ADS) and chemical fertilizer (CF) to flooded forage rice (Oryza sativa L.) in Japan were measured using a dynamic flow-through chamber method in lysimeters. The CF was applied at a rate of 300 N ha-¹ (three times) as ammoniacal-N fertilizer, and the ADS was applied to the lysimeters at total rates equivalent to 75, 100 and 150 kg N ha-¹, by broadcasting uniformly into the floodwater at three or six times (equal splits) between 17th June and 17th November, 2005. The emission fluxes for the first 2 days after application were very high from ADS, the highest values being 679 compared with a maximum of 156 mg N m-² d-¹ from CF. Most (61-93%) of the ammonia loss occurred during the first 5 days after each application of fertilizer. The total N loss as ammonia from ADS (29.6-51.7%) was much higher than from CF (12.2%). The highest fluxes were observed in August (2005) when air temperature was highest. More ammonia was lost from the ADS applied at the early stages (i.e. root taking, tiller stages) than at later stages (i.e. elongation, fruiting stages) of rice growth.

A novel system for organic waste stabilization and reuse, combined with production of nitrate-rich liquid fertilizer was developed by manure digestion followed by volatilization of ammonia-rich gas (originating in manure extract) and its nitrification and recovery. This approach has several advantages, including biowaste stabilization and high recovery (over 60%) of manure N mainly as nitrate which is a better N form for many plants as compared to ammonium as the sole fertilizer N. Moreover, the potential utilization of different wastes as N sources in organic horticulture is possible as well as removal of suspended particles and microorganisms (including pathogens) that might otherwise clog the irrigation system and pose health risks, respectively. In a pilot-scale study, the system yielded several hundred liters of nitrate-rich (ca. 11 g N L−1) liquid fertilizer using guano as substrate. In a fertilization experiment, lettuce fertigated with the nitrate-rich extract exhibited better growth and quality compared to the common organic practice of fertigation with guano extract. The resulting stabilized biowaste was estimated as “low-risk” according to current guidelines and may be used for liming or land application.

Inorganic fertilizers are used as agricultural countermeasures intended to inhibit the soil to plant transfer of radionuclides after a radioactive fallout. Two NH₄ ⁺ fertilizers, diammonium phosphate (DAP) and NPK, were applied to soil contaminated with a mixture of radionuclides to analyze whether they modify the transfer of ¹³⁷Cs, ⁹⁰Sr, and ⁶⁰Co and stable elements (K, Na, Ca, and Mg) to wheat plantlets grown under controlled laboratory conditions. DAP introduced NH₄ ⁺ in the soil, which can increase ¹³⁷Cs transfer, while NPK also introduced K⁺, which can decrease it. The application of DAP increased the accumulation of ¹³⁷Cs in wheat plantlets with increasing application rate, so did the ¹³⁷Cs/K in plantlets. Regarding the NPK application, the ¹³⁷Cs increased in all treatments, but at maximum rate, the available K introduced by the fertilizer was probably able to partially satisfy the nutritional requirements of the wheat plantlet and the ¹³⁷Cs decreased relative to the recommended rate. The ¹³⁷Cs/K ratio in plantlet decreased with increasing NPK rates. The transfer of ⁹⁰Sr increased with increasing DAP rate and only at the maximum NPK rate. The ⁶⁰Co transfer only increased at the maximum application rates for DAP and NPK. These modifications should be considered when using these fertilizers as agricultural countermeasures.