Marta Alfaro

Human activities emit nitrogen oxides (NO _x ≡ NO + NO ₂ ; with source emissions approximated as nitric oxide (NO)), potent air pollutants and short‐lived climate forcers, through direct and indirect pathways. Unlike direct releases, however, indirect NO _x emissions remain poorly understood and inadequately quantified. Here, by synthesizing available observations across global terrestrial ecosystems, we show that soil moisture and pH strongly affect the ratio of annual background NO to nitrous oxide (N ₂ O) emissions (), with a critical threshold at 46% water‐filled soil pore space. Combining soil moisture‐stratified modeled by machine learning with known indirect N ₂ O emission factors, global indirect NO _x emission factors () are derived, yielding an aggregated median of 1.59% (95% confidence interval (CI): 0.45%–2.41%) and significantly higher ( p < 0.01) disaggregated values of 1.77% (95% CI: 1.49%–2.61%) for wet climates () than those of 0.89% (95% CI: 0.45%–1.28%) for dry climates (). We further estimate that the global indirect NO _x emissions resulting from atmospheric deposition of nitrogen released by all anthropogenic sources amounted to approximately 886 (95% CI: 314–1639) Gg N year ⁻¹ (1 Gg = 10 ⁹ g) in 2015, with fertilization, animal husbandry, and other human activities contributing about 25%, 26%, and 49%, respectively. Crucially, without soil moisture stratification, the global indirect NO _x emissions would be underestimated by approximately 16% ( p < 0.001), while the associated uncertainty would be about 1.5 times as large. Our novel ‐based framework provides a robust approach for quantifying indirect NO _x emissions in regional, national and global inventories, thereby supporting targeted strategies to mitigate air pollution and climate change.

Purpose: Livestock production based on grazing is the most important productive activity in southern Chile. Most grasslands are located on volcanic soils with unexplained low nitrogen (N) leaching losses. Methods: A cutting field experiment was carried out between February 2008 and March 2010 on an Andisol of the Osorno soil series, testing liming (0 or 2 t CaCO₃ ha^− 1 yr^− 1) and N rate applied as inorganic fertiliser applied in two equal dressings (0, 200, 400 kg N ha^− 1 yr^− 1). Measurements of pasture yield, N uptake and N leaching losses were complemented with mineralization studies under field and laboratory conditions, and soil N abiotic retention. Results: Total N leaching losses were greater in the 400 kg N treatments (90 kg N ha^− 1, on average), with no differences between the liming treatments (10 kg N ha^− 1, on average; P > 0.05). Nitrogen addition resulted in 50% and 92% more dry matter yield in treatments receiving 200 and 400 kg N than the control (N-0) treatment. Potential N mineralization varied between 206 and 282 mg N kg^− 1 dry soil. The mineralization of more recalcitrant components of soil organic matter increased with both N and lime addition. Soil had a greater capacity to retain added N as ammonium (74% on average). Conclusions: The natural acidic soil conditions did not prevent nitrification, neither N leaching losses, probably associated to occurrence of N abiotic immobilization processes. Lime addition could influence N mineralization in the long term, while N addition would influence it in both short and long term.

Urease and nitrification inhibitors can reduce ammonia and greenhouse gas emissions from fertilizers and manure but their effectiveness depends on the conditions under which they are used. Consequently, it is essential for the credibility of emission reductions reported in regulatory emission inventories that their effectiveness is assessed under real-world conditions and not just in the laboratory. Here, we specify the criteria we consider necessary before the effects of inhibitors are included in regulatory emission inventories.

High nitrogen (N) fertiliser rates are usually applied to increase agricultural yields, leading to high nitrous oxide (N₂O) emissions. This is a greenhouse gas that contributes to climate change and depletes the ozone layer. This study aimed to optimise N use efficiency and quantify N₂O emission factors (EF1) by measuring the effect of N rates on the yield of a potato-cover crop rotation, apparent N use efficiency (NUE) and N₂O emissions. The two-year experiment was carried out on volcanic soils (1.6% carbon, 1.4% N) in southern Chile (40°52′ S, 73°03′ W). Three N application rates were evaluated (80, 150 and 300 kg N ha⁻¹), 35% of which was applied at the planting stage (granular) and 65% at the tubering stage. A control treatment with no N addition was also included. Reducing N fertilisation to 80 kg N ha⁻¹ increased NUE by three times, reduced N₂O-N emissions by 33% and reduced emission intensity by 27% without a detrimental impact on crop yield and marketable tuber calibre. No significant difference (p < 0.05) was observed in the N₂O emission factor (EF1) because of a low rainfall year. The results suggest that in rainfed agriculture systems, N fertiliser application can be significantly reduced without sacrificing potato yield, favouring the economic and environmental sustainability of potato production.

Livestock manure management systems can be significant sources of nitrous oxide (N₂O), methane (CH₄), and ammonia (NH₃) emissions. Many studies have been conducted to improve our understanding of the emission processes and to identify influential variables in order to develop mitigation techniques adapted to each manure management step (animal housing, outdoor storage, and manure spreading to land). The international project DATAMAN (http://www.dataman.co.nz) aims to develop a global database on greenhouse gases (N₂O, CH₄) and NH₃ emissions from the manure management chain to refine emission factors (EFs) for national greenhouse gas and NH₃ inventories. This paper describes the housing and outdoor storage components of this database. Relevant information for different animal categories, manure types, livestock buildings, outdoor storage, and climatic conditions was collated from published peer reviewed research, conference papers, and existing databases published between 1995 and 2021. In the housing database, 2024 EFs were collated (63% for NH₃, 19.5% for CH₄, and 17.5% for N₂O). The storage database contains 654 NH₃ EFs from 16 countries, 243 CH₄ EFs from 13 countries, and 421 N₂O EFs from 17 countries. Across all gases, dairy cattle and swine production in temperate climate zones are the most represented animal and climate categories. As for the housing database, the number of EFs for the tropical climate zone is under‐represented. The DATAMAN database can be used for the refinement of national inventories and better assessment of the cost‐effectiveness of a range of mitigation strategies.

The increase in global average temperature has significant implications for food security and agriculture production. Grass species adapted to new climate scenarios are essential for the success of livestock production. The aim of this study was to evaluate different forage species, providing animal feed during critical dry periods as an adaptation strategy for livestock grazing systems, and its implications for greenhouse gas (GHG) emissions. The field experiment was conducted during September 2015 to September 2017, with four treatments (n = 5, completely randomized block design), including two perennial forages, Bromus valdivianus (Bromus), Lotus corniculatus (Lotus), alone and in a mixture pasture (Br/L). As a control treatment, the forage species commonly seeded by the farmer was used (hybrid ryegrasses + Oat, Control). One-half of the plots was used for nitrous oxide (N₂O) and methane (CH₄) measurements, and the remaining half for destructive soil and forage sampling. Gas fluxes were measured using the static chambers technique. Cumulative emissions of N–N₂O, C–CH₄ and CO_2−eq were not affected by treatments, averaging 1.7 kg N–N₂O ha⁻¹, 3.2 kg C–CH₄ ha⁻¹ and 635.5 kg CO₂ ha⁻¹, respectively (p > 0.05). However, emission intensity tended to be lower for Br/L compared with other treatments (p = 0.06) during the second year, while pasture yield was greater for Br/L (p < 0.05). The control showed a greater average pasture yield (first and second years) compared to other treatments, with the highest metabolizable energy and the lowest crude protein content. Our results suggest that a mix pasture Br/L as a management strategy would promote farm adaptation, given that it favors pasture yield at critical dry periods during the year. This inclusion also reduces N–N₂O emissions from grassland soils as well as favoring C–CH₄ capture. Our study determined that N–N₂O and C–CH₄ emissions were regulated by soil variables, mainly soil moisture and soil temperature. Extension and knowledge transfer should be provided to farmers to account for potential adoption barriers, such as low short-term yield.

Increasing rates of nitrogen (N) conventional fertilizer have led to increasing risks of N losses to the atmosphere, mainly as ammonia (NH₃) and nitrous oxide (N₂O). The aim of this study was to evaluate the effect of foliar N-based nanoformulations on the dynamics of N₂O and NH₃ emissions from grasslands. Six N treatments (50 kg N ha⁻¹) plus a control (n = 4) were tested on a completely randomized design: granular urea (Urea-g), dissolved urea (Urea-d), dissolved ammonium nitrate (NH₄NO₃), and nitrate-, urea-, and ammonium-based nanoformulations (NO₃-F, Urea-F, NH₄-F) applied as foliar spray to intact soil cores maintained under controlled conditions. In addition, a control N = 0 was included. Cumulative emissions of N₂O and NH₃ (mg N m⁻²) were measured using dynamic/static chambers. Effects on yield and soil available N were also quantified. Volatilization of NH₃ was the main N loss pathway (ranged from 2 to 51% of the N applied). Higher emissions were observed with NH₄-F and low emissions in the nitrate-based fertilizers. Direct N₂O losses were low compared to NH₃ losses, varying between 0.07 and 0.25% of the N applied. Due to high NH₃ losses, indirect N₂O losses were 0.3 to 2.8 times greater than direct N₂O losses. There was no effect of N treatments on soil available N or pasture yield. The application of a NO₃-foliar formulation emerges as a potential alternative for the mitigation of integrated N gaseous emissions. Ammonium-based nanoformulations require improvements in order to reduce losses. Further studies should include yield evaluations under field conditions, cost–benefit analysis, and potential impacts in the agri-food chain.

Nitrogen that is excreted through the urine and dung of cattle is an important source of nitrous oxide and ammonia emissions. In Chile, several studies have evaluated nitrogen (N) intake and its partitioning into urine and dung from beef and dairy cattle, however, there are no studies collating all data into one central database, which would allow an estimation of N excretion and its key variables to be developed. The aim of this study was to determine the N partition (milk or meat, urine and dung) and variables influencing the nitrogen use efficiency (NUE) and urinary N excretion of cattle based on a database generated from Chilean studies. The search of studies was carried out using a keyword list in different web-based platforms. Nitrogen excretion into urine and dung was calculated using equations reported in the literature for beef and dairy cattle. Mixed models were used to identify variables influencing the N partitioning. Nitrogen intake and its partitioning into the animal product, urine and dung were higher for dairy compared to beef cattle. For dairy cattle, NUE was influenced by milk yield, the non-fibrous carbohydrates (NFC)/crude protein ratio, acid detergent fiber intake and milk urea N (MUN), while urinary N excretion was influenced by milk yield, MUN and NFC intake. For beef cattle, N intake and its excretion were greater for grazing compared to the confined system, while NUE was greater for confined animals. This database supplies new information on N intake and its partitioning (milk, meat, urine and dung) for dairy and beef cattle, which can be used for the estimation of greenhouse gas emissions from pasture-based livestock in Chile. Additionally, our study supplies new information on nutritional variables determining NUE and urinary N excretion for dairy cattle, which can be used by farmers to reduce N excretion into the environment.

Manure application to land and deposition of urine and dung by grazing animals are major sources of ammonia (NH₃) and nitrous oxide (N₂O) emissions. Using data on NH₃ and N₂O emissions following land‐applied manures and excreta deposited during grazing, emission factors (EFs) disaggregated by climate zone were developed, and the effects of mitigation strategies were evaluated. The NH₃ data represent emissions from cattle and swine manures in temperate wet climates, and the N₂O data include cattle, sheep, and swine manure emissions in temperate wet/dry and tropical wet/dry climates. The NH₃ EFs for broadcast cattle solid manure and slurry were 0.03 and 0.24 kg NH₃–N kg^–1 total N (TN), respectively, whereas the NH₃ EF of broadcast swine slurry was 0.29. Emissions from both cattle and swine slurry were reduced between 46 and 62% with low‐emissions application methods. Land application of cattle and swine manure in wet climates had EFs of 0.005 and 0.011 kg N₂O–N kg^–1 TN, respectively, whereas in dry climates the EF for cattle manure was 0.0031. The N₂O EFs for cattle urine and dung in wet climates were 0.0095 and 0.002 kg N₂O–N kg^–1 TN, respectively, which were three times greater than for dry climates. The N₂O EFs for sheep urine and dung in wet climates were 0.0043 and 0.0005, respectively. The use of nitrification inhibitors reduced emissions in swine manure, cattle urine/dung, and sheep urine by 45–63%. These enhanced EFs can improve national inventories; however, more data from poorly represented regions (e.g., Asia, Africa, South America) are needed.