Experimental field estimation of organic nitrogen formation in tree canopies

The content of organic N has been shown in many studies to increase during the passage of rain water through forest canopies. The source of this organic N is unknown, but generally assumed to come from canopy processing of wet or dry-deposited inorganic N. There have been very few experimental studies in the field to address the canopy formation or loss of organic N. We report two studies: a Scots pine canopy exposed to ammonia gas, and a Sitka spruce canopy exposed to ammonium and nitrate as wet deposition. In both cases, organic N deposition in throughfall was increased, but only represented a small fraction (<10%) of the additional inorganic N supplied, suggesting a limited capacity for net organic N production, similar in both conifer canopies under Scottish summertime conditions, of less than 1.6 mmol N m⁻² mth⁻¹ (equivalent to 3 kg N ha⁻¹ y⁻¹).     

Emissions of gaseous nitrogen species from manure management: a new approach

A procedure for the assessment of emissions of nitrogen (N) species (ammonia, nitrous oxide, nitric oxide, di-nitrogen) from the manure management system is developed, which treats N pools and flows including emissions strictly according to conservation of mass criteria. As all relevant flows in the husbandry of mammals are depicted, the methodology is considered a Tier 3 approach in IPCC terminology or a detailed methodology in UN ECE terminology. The importance of accounting for all N species is illustrated by comparing emission estimates obtained using this approach with those obtained from the application the present detailed/Tier 2 methodology.     

Interpreting nitrogen pollution thresholds for sensitive habitats: the importance of concentration versus dose

Nitrate and ammonium concentration in wet deposition detrimentally impacted a sensitive pollution indicator species irrespective of the nitrogen dose.     

Alterations in soil microbial activity and N-transformation processes due to sulfadiazine loads in pig-manure

Most veterinary drugs enter the environment via manure application. However, it is unclear how these substances interact with soil biota. Therefore, it was the aim of the present study to investigate the effects of manure containing different concentrations of the antibiotic sulfadiazine (SDZ) on the soil microbial communities. It was shown that manure alone has a stimulating effect on microbial activity. Only potential nitrification was negatively influenced by manure application. The addition of SDZ to the manure reduced microbial activity. Depending on the SDZ concentration, levels of activity were in the range of the control soil without manure application. Also, selected processes in nitrogen turnover were negatively influenced by the addition of SDZ to the manure, with nitrification being the only exception. The effects were visible for up to 4 days after application of the manure with or without SDZ and were correlated with the bioavailability of the antibiotic.     

A classification and regression tree model of controls on dissolved inorganic nitrogen leaching from European forests

Often, there is a non-linear relationship between atmospheric dissolved inorganic nitrogen (DIN) input and DIN leaching that is poorly captured by existing models. We present the first application of the non-parametric classification and regression tree approach to evaluate the key environmental drivers controlling DIN leaching from European forests. DIN leaching was classified as low (<3), medium (3-15) or high (>15 kg N ha⁻¹ year⁻¹) at 215 sites across Europe. The analysis identified throughfall NO₃⁻ deposition, acid deposition, hydrology, soil type, the carbon content of the soil, and the legacy of historic N deposition as the dominant drivers of DIN leaching for these forests. Ninety four percent of sites were successfully classified into the appropriate leaching category. This approach shows promise for understanding complex ecosystem responses to a wide range of anthropogenic stressors as well as an improved method for identifying risk and targeting pollution mitigation strategies in forest ecosystems.     

Atmospheric transport of urban-derived NH(x): Evidence from nitrogen concentration and delta(15)N in epilithic mosses at Guiyang, SW China

Nitrogen concentration and δ¹⁵N in 175 epilithic moss samples were investigated along four directions from urban to rural sites in Guiyang, SW China. The spatial variations of moss N concentration and δ¹⁵N revealed that atmospheric N deposition is dominated by NH_x-N from two major sources (urban sewage NH₃ and agricultural NH₃), the deposition of urban-derived NH_x followed a point source pattern characterized by an exponential decline with distance from the urban center, while the agricultural-derived NH_x was shown to be a non-point source. The relationship between moss N concentration and distance (y = 1.5e^−0.13x + 1.26) indicated that the maximum transporting distance of urban-derived NH_x averaged 41 km from the urban center, and it could be determined from the relationship between moss δ¹⁵N and distance [y = 2.54 ln(x) − 12.227] that urban-derived NH_x was proportionally lower than agricultural-derived NH_x in N deposition at sites beyond 17.2 km from the urban center. Consequently, the variation of urban-derived NH_x with distance from the urban center could be modeled as y = 56.272e^−0.116x − 0.481 in the Guiyang area.     

Influence of solar UV radiation on the nitrogen metabolism in needles of Scots pine (Pinus sylvestris L.)

Needles of 20-year-old Scots pine (Pinus sylvestris L.) saplings were studied in an ultraviolet (UV) exclusion field experiment (from 2000 to 2002) in northern Finland (67 °N). The chambers held filters that excluded both UV-B and UV-A, excluded UV-B only, transmitted all UV (control), or lacked filters (ambient). UV-B/UV-A exclusion decreased nitrate reductase (NR) activity of 1-year-old needles of Scots pines compared to the controls. The proportion of free amino acids varied in the range 1.08-1.94% of total proteins, and was significantly higher in needles of saplings grown under UV-B/UV-A exclusion compared to the controls or UV-B exclusion. NR activity correlated with air temperature, indicating a “chamber effect”. The study showed that both UV irradiance and increasing temperature are significant modulators of nitrogen (N) metabolism in Scots pine needles.     

Bottom-up uncertainty estimates of global ammonia emissions from global agricultural production systems

Here we present an uncertainty analysis of NH₃ emissions from agricultural production systems based on a global NH₃ emission inventory with a 5×5 min resolution. Of all results the mean is given with a range (10% and 90% percentile). The uncertainty range for the global NH₃ emission from agricultural systems is 27–38 (with a mean of 32) Tg NH₃-N yr⁻¹, N fertilizer use contributing 10–12 (11) Tg yr⁻¹ and livestock production 16–27 (21) Tg yr⁻¹. Most of the emissions from livestock production come from animal houses and storage systems (31–55%); smaller contributions come from the spreading of animal manure (23–38%) and grazing animals (17–37%). This uncertainty analysis allows for identifying and improving those input parameters with a major influence on the results. The most important determinants of the uncertainty related to the global agricultural NH₃ emission comprise four parameters (N excretion rates, NH₃ emission rates for manure in animal houses and storage, the fraction of the time that ruminants graze and the fraction of non-agricultural use of manure) specific to mixed and landless systems, and total animal stocks. Nitrogen excretion rates and NH₃ emission rates from animal houses and storage systems are shown consistently to be the most important parameters in most parts of the world. Input parameters for pastoral systems are less relevant. However, there are clear differences between world regions and individual countries, reflecting the differences in livestock production systems.     

施肥后土壤HONO排放特征及排放因子研究

近年发现土壤可以排放亚硝酸（HONO）,对大气氧化性具有潜在的重要影响.施肥能增加土壤含氮气体的排放,通常用排放因子表征气体排放量对化肥的响应关系.但HONO的相关研究尚为空白,制约了对这一新的地气交换机制的环境效应的评估.为此,在珠三角对一块菜地施用3种化肥（复合肥、碳酸氢铵和尿素）,利用动态箱测量施肥前后的HONO排放通量.结果表明,土壤施用3种氮肥后的最大HONO排放通量分别为23.1、19.5和57.4 ng·m-2·s-1,分别是施肥前最大值的3.5、3.2和9.4倍;3种氮肥的HONO排放因子分别为8.60×10-5、1.44×10-4和2.48×10-4;施肥后HONO排放通量呈现白天高夜间低的特征,且与土壤温度、土壤孔隙含水量（WFPS,在低含水量区间）呈正相关关系.证实了施肥对HONO排放具有显著促进作用,通过外场实测获得的3种化肥HONO排放因子,将为编制HONO排放清单等后续研究提供依据.     

通过农产品质量认证的合作社影响农业化肥用量的理论机制与实证分析

化肥减量施用是实现中国农产品质量安全与农业绿色高质量发展的重要举措之一,而小规模分散化的经营格局不利于化肥减量技术的推广使用。农民合作社是弥补小规模经营不足与实施农产品质量认证的重要制度安排,其能否以及如何促进农业化肥减量是当前亟待回答的重大现实问题。本文阐明了通过农产品质量认证的合作社对农业化肥用量的影响及作用机制,并基于2007—2018年中国30个省级（市、自治区）面板数据展开实证分析。研究结果表明：通过农产品质量认证的合作社存在显著的化肥减施效应,其主要通过质量溢价、组织规范、组织支持传导路径实现农业化肥减量。从区域差异看,在化肥用量处于高分位点的省份,通过农产品质量认证的合作社表现出更为显著的化肥减施效应;从农作物差异看,通过农产品质量认证的合作社对农业化肥减量施用的贡献主要来自水稻、小麦、玉米三大粮食作物,以及棉花、甘蔗、苹果、柑子四类经济作物的化肥减施效应。