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1. Meta‐analysis on the potential for increasing nitrogen losses from intensifying tropical agriculture

   https://doi.org/10.1111/gcb.14951  

   Huddell, Alexandra M.; Galford, Gillian L.; Tully, Katherine L.; Crowley, Cynthia; Palm, Cheryl A.; Neill, Christopher; Hickman, Jonathan E.; Menge, Duncan N. L. (January 2020, Global Change Biology)

   Abstract Fertilized temperate croplands export large amounts of reactive nitrogen (N), which degrades water and air quality and contributes to climate change. Fertilizer use is poised to increase in the tropics, where widespread food insecurity persists and increased agricultural productivity will be needed, but much less is known about the potential consequences of increased tropical N fertilizer application. We conducted a meta‐analysis of tropical field studies of nitrate leaching, nitrous oxide emissions, nitric oxide emissions, and ammonia volatilization totaling more than 1,000 observations. We found that the relationship between N inputs and losses differed little between temperate and tropical croplands, although total nitric oxide losses were higher in the tropics. Among the potential drivers we studied, the N input rate controlled all N losses, but soil texture and water inputs also controlled hydrological N losses. Irrigated systems had significantly higher losses of ammonia, and pasture agroecosystems had higher nitric oxide losses. Tripling of fertilizer N inputs to tropical croplands from 50 to 150 kg N ha⁻¹ year⁻¹would have substantial environmental implications and would lead to increases in nitrate leaching (+30%), nitrous oxide emissions (+30%), nitric oxide (+66%) emissions, and ammonia volatilization (+74%), bringing tropical agricultural nitrate, nitrous oxide, and ammonia losses in line with temperate losses and raising nitric oxide losses above them. 

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2. A “toy model” analysis of causes of nitrogen limitation in terrestrial ecosystems

   https://doi.org/10.1007/s10533-022-00959-z  

   Vitousek, Peter M.; Treseder, Kathleen K.; Howarth, Robert W.; Menge, Duncan N. L. (August 2022, Biogeochemistry)

   Abstract Nitrogen (N) limitation to net primary production is widespread and influences the responsiveness of ecosystems to many components of global environmental change. Logic and both simple simulation (Vitousek and Fieldin in Biogeochemistry 46: 179–202, 1999) and analytical models (Menge in Ecosystems 14:519–532, 2011) demonstrate that the co-occurrence of losses of N in forms that organisms within an ecosystem cannot control and barriers to biological N fixation (BNF) that keep this process from responding to N deficiency are necessary for the development and persistence of N limitation. Models have focused on the continuous process of leaching losses of dissolved organic N in biologically unavailable forms, but here we use a simple simulation model to show that discontinuous losses of ammonium and nitrate, normally forms of N whose losses organisms can control, can be uncontrollable by organisms and can contribute to N limitation under realistic conditions. These discontinuous losses can be caused by temporal variation in precipitation or by ecosystem-level disturbance like harvest, fire, and windthrow. Temporal variation in precipitation is likely to increase and to become increasingly important in causing N losses as anthropogenic climate change proceeds. We also demonstrate that under the conditions simulated here, differentially intense grazing on N- and P-rich symbiotic N fixers is the most important barrier to the responsiveness of BNF to N deficiency. 

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3. Disparities in nitrogen and phosphorus management across time and space: a case study of the Chesapeake Bay using the CAFE framework

   https://doi.org/10.1088/1748-9326/ad786c  

   Zou, Tan; Davidson, Eric_A; Sabo, Robert_D; MacDonald, Graham_K; Zhang, Xin (September 2024, Environmental Research Letters)

   Abstract Efficient management of nitrogen (N) and phosphorus (P) is imperative for sustainable agriculture, resource conservation, and reducing environmental pollution. Despite progress in on-farm practices and urban wastewater treatment in the Chesapeake Bay (CB) watershed, limited attention has been given to nutrient transport, use, and handling between farms and urban environments. This study uses the hierarchicalCAFE(Cropping system, Animal-crop system, Food system, and Ecosystem) framework to evaluate nutrient management performances within the watershed. We first develop a three-decade, county-level nutrient budget database (1985–2019), then analyze the spatiotemporal patterns of N and P budgets, as well as N and P use efficiencies, within the fourCAFEhierarchies. Our results indicate a sizable increase in potential N and P losses beyond crop fields (i.e. in the Animal-crop system, Food system, and Ecosystem), surpassing losses from cropland in over 90% of counties. To address these system-wide trade-offs, we estimate the nutrient resources in waste streams beyond croplands, which, if recovered and recycled, could theoretically offset mineral fertilizer inputs in over 60% of counties. Additionally, the growing imbalance in excess N versus P across systems, which increases the N:P ratio of potential losses, could pose an emerging risk to downstream aquatic ecosystems. By utilizing a systematic approach, our novel application of theCAFEframework reveals trade-offs and synergies in nutrient management outcomes that transcend agro-environmental and political boundaries, underscores disparities in N and P management, and helps to identify unique opportunities for enhancing holistic nutrient management across systems within the CB watershed. 

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4. Dissolved and gaseous nitrogen losses in forests controlled by soil nutrient stoichiometry

   https://doi.org/10.1088/1748-9326/ac007b  

   Oulehle, Filip; Goodale, Christine L; Evans, Christopher D; Chuman, Tomáš; Hruška, Jakub; Krám, Pavel; Navrátil, Tomáš; Tesař, Miroslav; Ač, Alexandr; Urban, Otmar; et al (May 2021, Environmental Research Letters)

   Abstract Global chronic nitrogen (N) deposition to forests can alleviate ecosystem N limitation, with potentially wide ranging consequences for biodiversity, carbon sequestration, soil and surface water quality, and greenhouse gas emissions. However, the ability to predict these consequences requires improved quantification of hard-to-measure N fluxes, particularly N gas loss and soil N retention. Here we combine a unique set of long-term catchment N budgets in the central Europe with ecosystem 15 N data to reveal fundamental controls over dissolved and gaseous N fluxes in temperate forests. Stream leaching losses of dissolved N corresponded with nutrient stoichiometry of the forest floor, with stream N losses increasing as ecosystems progress towards phosphorus limitation, while soil N storage increased with oxalate extractable iron and aluminium content. Our estimates of soil gaseous losses based on 15 N stocks averaged 2.5 ± 2.2 kg N ha −1 yr −1 and comprised 20% ± 14% of total N deposition. Gaseous N losses increased with forest floor N:P ratio and with dissolved N losses. Our relationship between gaseous and dissolved N losses was also able to explain previous 15 N-based N loss rates measured in tropical and subtropical catchments, suggesting a generalisable response driven by nitrate (NO 3 − ) abundance and in which the relative importance of dissolved N over gaseous N losses tended to increase with increasing NO 3 − export. Applying this relationship globally, we extrapolated current gaseous N loss flux from forests to be 8.9 Tg N yr −1 , which represent 39% of current N deposition to forests worldwide. 

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5. Mismatches between ammonium and nitrate losses at the field and watershed scales suggest contrasting controls in two agricultural watersheds. https://doi.org/10.1016/j.agee.2025.109531

   Vincent, Anna; Tank, JL; Pruitt, A; Spier, S; Mahl, U; Sethna, L; Rasnake, L; Royer, T (May 2025, Agriculture, Ecosystems & Environment)

   Nitrogen (N) fertilizer enhances crop production, but field runoff impacts water quality in adjacent freshwaters. Planting winter cover crops reduces nitrate-N losses during the fallow period, but less is known about impacts on ammonium-N. From 2016–2023, we sampled biweekly from the Shatto Ditch and Kirkpatrick Ditch Watersheds in Indiana (USA) to compare the impact of cover crops on dissolved inorganic nitrogen at the field-, edge-of-field, and watershed-scales. We measured soil ammonium-N and nitrate-N, biomass, and organic matter in fall and spring. Cover crops reduced soil ammonium-N at Shatto and soil nitrate-N in both watersheds. Tile losses and watershed yields of ammonium-N occurred on scales orders of magnitude lower than nitrate-N. Tile ammonium-N losses from cover cropped fields ranged from 97 % lower to 31 % higher at Shatto, and 45 % lower to 75 % higher at Kirkpatrick compared to those without. Cover crops reduced field-scale nitrate-N losses at Shatto by 58–87 %, but losses at Kirkpatrick ranged 99 % lower to 15 % higher. Tile flow explained interannual variation in nitrate-N losses, while field-scale ammonium-N losses were driven by soil and microbial interactions and mobilization during storms. Watershed-scale ammonium-N and nitrate-N yields correlated with runoff (Kendall τ=0.45 and 0.39, respectively). While nitrate-N yields mirrored runoff, ammonium-N yields exhibited a step-functional increase, pointing to the importance of storms as a driver of loss. As Midwest crop production adapts to fluctuating environmental conditions, we demonstrate how applying cover crops over a multi-year period can mitigate ammonium-N losses 

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