Intense Warming Will Significantly Increase Cropland Ammonia Volatilization Threatening Food Security and Ecosystem Health

Climate change exacerbates the environmental impacts of agriculture

Agriculture's global environmental impacts are widely expected to continue expanding, driven by population and economic growth and dietary changes. This Review highlights climate change as an additional amplifier of agriculture's environmental impacts, by reducing agricultural productivity, reducing the efficacy of agrochemicals, increasing soil erosion, accelerating the growth and expanding the range of crop diseases and pests, and increasing land clearing. We identify multiple pathways through which climate change intensifies agricultural greenhouse gas emissions, creating a potentially powerful climate change-reinforcing feedback loop. The challenges raised by climate change underscore the urgent need to transition to sustainable, climate-resilient agricultural systems. This requires investments that both accelerate adoption of proven solutions that provide multiple benefits, and that discover and scale new beneficial processes and food products.

Impacts assessment of nitrification inhibitors on U.S. agricultural emissions of reactive nitrogen gases

Fertilizer-intensive agriculture leads to emissions of reactive nitrogen (Nr), posing threats to climate via nitrous oxide (N2O) and to air quality and human health via nitric oxide (NO) and ammonia (NH3) that form ozone and particulate matter (PM) downwind. Adding nitrification inhibitors (NIs) to fertilizers can mitigate N2O and NO emissions but may stimulate NH3 emissions. Quantifying the net effects of these trade-offs requires spatially resolving changes in emissions and associated impacts. We introduce an assessment framework to quantify such trade-off effects. It deploys an agroecosystem model with enhanced capabilities to predict emissions of Nr with or without the use of NIs, and a social cost of greenhouse gas to monetize the impacts of N2O on climate. The framework also incorporates reduced-complexity air quality and health models to monetize associated impacts of NO and NH3 emissions on human health downwind via ozone and PM. Evaluation of our model against available field measurements showed that it captured the direction of emission changes but underestimated reductions in N2O and overestimated increases in NH3 emissions. The model estimated that, averaged over applicable U.S. agricultural soils, NIs could reduce N2O and NO emissions by an average of 11% and 16%, respectively, while stimulating NH3 emissions by 87%. Impacts are largest in regions with moderate soil temperatures and occur mostly within two to three months of N fertilizer and NI application. An alternative estimate of NI-induced emission changes was obtained by multiplying the baseline emissions from the agroecosystem model by the reported relative changes in Nr emissions suggested from a global meta-analysis: -44% for N2O, -24% for NO and +20% for NH3. Monetized assessments indicate that on an annual scale, NI-induced harms from increased NH3 emissions outweigh (8.5-33.8 times) the benefits of reducing NO and N2O emissions in all agricultural regions, according to model-based estimates. Even under meta-analysis-based estimates, NI-induced damages exceed benefits by a factor of 1.1-4. Our study highlights the importance of considering multiple pollutants when assessing NIs, and underscores the need to mitigate NH3 emissions. Further field studies are needed to evaluate the robustness of multi-pollutant assessments.

Modeling ammonia emissions from manure in conventional, organic, and grazing dairy systems and practices to mitigate emissions

Almost 60% of all ammonia (NH3) emissions are from livestock manure. Understanding the sources and magnitude of NH3 emissions from manure systems is critical to implement mitigation strategies. This study models 13 archetypical conventional (5 farms), organic (5 farms), and grazing (3 farms) dairy farms to estimate NH3 emissions from manure at the barn, storage, and after land application. Mitigation practices related to management of the herd, crop production, and manure are subsequently modeled to quantify the change in NH3 emissions from manure by comparing archetypical practices with these alternative practices. A mass balance of nutrients is also conducted. Emissions per tonne of excreted manure for the manure system (barn, storage, and land application) range from 3.0 to 4.4 g of NH3 for conventional farms, 3.5 to 4.4 g of NH3 for organic farms, and 3.4 to 3.9 g of NH3 for grazing farms. For all farm types, storage and land application are the main sources of NH3 emissions from manure. In general, solid manures have higher emission intensities due to higher pH during storage (pH = 7.4 for liquid, 7.8 for slurry, and 8.5 for solid manure) and lower infiltration rates after land application when compared with slurry and liquid manures. The most effective management practices to reduce NH3 emissions from manure systems are combining solid-liquid separation with manure injection (up to 49% reduction in NH3 emissions), followed by injection alone, and reducing crude protein in the dairy ration, especially in organic and grazing farms that have grazing and forages as the main component of the dairy ration. This study also shows that the intensity of NH3 emissions from manure depends significantly on the functional unit and presents results per manure excreted, total solids in excreted manure, animal units, and fat- and protein-corrected milk.

Linking health to geology-a new assessment and zoning model based on the frame of medical geology

With the growing concerns about the Earth's environment and human health, there has been a surge in research focused on the intersection of health and geology. This study quantitatively assesses the relationship between human health and geological factors using a new framework. The framework considers four key geological environment indicators related to health: soil, water, geological landform, and atmosphere. Results indicate that the atmospheric and water resource indicators in the study area were generally favorable, while the scores of geological landforms varied based on topography. The study also found that the selenium content in the soil greatly exceeded the local background value. Our research underscores the importance of geological factors on human health, establishes a new health-geological assessment model, and provides a scientific foundation for local spatial planning, water resource development, and land resource management. However, due to varying geological conditions worldwide, the framework and indicators for health geology may need to be adjusted accordingly.

Atmospheric ammonia in China: Long-term spatiotemporal variation, urban-rural gradient, and influencing factors

In recent years, atmospheric ammonia (NH₃) concentrations have increased in China. Ammonia control has become one of the next hot topics in air pollution mitigation with the increasing cost of acid gas emission reduction. In this study, using Infrared Atmospheric Sounding Interferometer (IASI) satellite observations, we analyzed the spatiotemporal distribution, the urban-rural gradient of the vertical column densities (VCDs) of NH₃ and the contribution of influencing factors (meteorology, social, atmospheric acid gases, and NH₃ emissions) in China from 2008 to 2019 using hotspot analysis, circular gradient analysis, geographical and temporal weighted regression, and some other methods. Our results showed that NH₃ VCDs in China have significantly increased (31.88 %) from 2008 to 2019, with the highest occurring in North China Plain. The average NH₃ VCDs in urban areas were significantly higher than those in rural areas, and the urban-rural gap in NH₃ VCDs was widening. The results of circular gradient analysis showed an overall decreasing trend in NH₃ VCDs along the urban-rural gradient. We used a geographically and temporally weighted regression model to analyze the contribution of various influencing factors to NH₃ VCDs: meteorology (30.13 %), social (27.40 %), atmospheric acid gases (23.20 %), and NH₃ emissions (19.28 %) factors. The results showed substantial spatiotemporal differences in the influencing factors. Atmospheric acid gas was the main reason for the increase in NH₃ VCDs from 2008 to 2019. A more thorough understanding of the spatiotemporal distribution, urban-rural variations, and factors influencing NH₃ in China will aid in developing control strategies to reduce PM_2.5.

Nitrogen management to minimize yield-scaled ammonia emission from paddy rice in the Middle and Lower Yangtze River Basin: A meta-analysis

Paddy fields in China contributed to one third of the global cropland ammonia (NH₃) emission inventory, while rice accounted for half of cereal consumption, necessitating exhaustive considerations of the balance between NH₃ emissions abatement and food demand. The concept of yield-scaled emission intensity (emissions per unit crop production) has the potential to guide sustainable intensification strategies, yet its application to NH₃ emissions remains poorly understood. Here, by constructing novel crop-specific models for single rice production and NH₃ emissions in the Middle and Lower Yangtze River Basin (LYRB) as a case study, the relationships between fertilizer N application and yield-scaled NH₃ were estimated. Contrary to our hypothesis of a tipping point, our results showed that yield-scaled NH₃ curves could not directly identify optimal nitrogen (N) rates. However, the benefit of lower N fertilizer rate on NH₃ abatement consistently outweighed the risk of yield loss. The exponential relationships between yield-scaled NH₃ and N surplus allowed us to estimate the N surplus criterion as 15.6 kg N ha^-1 (or 190 kg N ha^-1 fertilizer N rate) for the LYRB. Under the N surplus criterion, NH₃ emissions can be reduced by 23-27% without severely impacting rice yield, compared to the N rate required for the highest yield. Moreover, five major controlling factors for yield-scaled NH₃ were estimated by random forest models, ranked in order of importance as N rate, total N, K rate, mean annual precipitation, and soil organic carbon. Among the agricultural practices (irrigation, tillage, and fertilizer management), deep placement was the most effective measure to reduce yield-scaled NH_3, showing 48% reduction potential, followed by proper N splitting frequency (43%). Overall, this study highlights the efficacy of N application optimization and targeted farm management in mitigating NH₃ emission while maintaining crop productivity.

Impact of cattle slurry application methods on ammonia losses and grassland nitrogen use efficiency

Optimal manure management is required to ensure efficient nutrient supply to farmland and to avoid adverse environmental impacts. Accordingly, ammonia (NH₃) emissions associated with different slurry application techniques were investigated in grassland trials under different soil and weather conditions across Germany. Cattle slurry was applied in two dressings, early in spring and after the first silage cut, with a target amount of 170 kg N ha^-1. The application treatments comprised: trailing shoe (TS), acidified slurry applied with trailing shoe (TS + A), open slot injection (SI), and slurry treated with a nitrification inhibitor (NI) applied by slot injection (SI + NI). In addition, slurry application techniques were compared with a non-N-fertilized control and a mineral fertilizer treatment (calcium ammonium nitrate, CAN). NH₃ measurements followed each N application event. NH₃ losses were equivalent to 1-39% of total ammoniacal nitrogen (TAN) applied. The average NH₃ mitigation potential of the different slurry application techniques compared to TS was 45.7 ± 7, 21.2 ± 6.2 and 13.7 ± 8.2% for TS + A, SI and SI + NI, respectively. The use of nitrification inhibitor with slot injected slurry did not increase NH₃ losses relative to TS (p > 0.05). Mean apparent N use efficiency was two times higher for CAN (49%) than the slurry treatments (24%) but was comparable between SI + NI and CAN in five out of the eight cases. Our results indicate that mean TAN related NH₃ emissions of tested treatments (3.3, 22.6, 12.2, 17.8 and 19.3% for CAN, TS, TS + A, SI and SI + NI, respectively) were generally lower than described in previous studies. Moreover, the results suggested possible increases in NH₃ mitigation and N use efficiency when cattle slurry is applied with acidification or injection techniques. We found no evidence that NI addition to slot injected slurry, a treatment discussed as a measure to reduce N₂O emission and nitrate leaching, changed NH₃ emission.

Integrated Modeling of U.S. Agricultural Soil Emissions of Reactive Nitrogen and Associated Impacts on Air Pollution, Health, and Climate

Agricultural soils are leading sources of reactive nitrogen (Nr) species including nitrogen oxides (NO_x), ammonia (NH₃), and nitrous oxide (N₂O). The propensity of NO_x and NH₃ to generate ozone and fine particulate matter and associated impacts on health are highly variable, whereas the climate impacts of long-lived N₂O are independent of emission timing and location. However, these impacts have rarely been compared on a spatially resolved monetized basis. In this study, we update the nitrogen scheme in an agroecosystem model to simulate the Nr emissions from fertilized soils across the contiguous United States. We then apply a reduced-form air pollution health effect model to assess air quality impacts from NO_x and NH₃ and a social cost of N₂O to assess the climate impacts. Assuming an $8.2 million value of a statistical life and a $13,100/ton social cost of N₂O, the air quality impacts are a factor of ∼7 to 15 times as large as the climate impacts in heavily populated coastal regions, whereas the ratios are closer to 2.5 in sparsely populated regions. Our results show that air pollution, health, and climate should be considered jointly in future assessments of how farming practices affect Nr emissions.

Banana, pineapple, cassava and sugarcane residue biochars cannot mitigate ammonia volatilization from latosols in tropical farmland

Ammonia (NH₃) volatilization is a major pathway of soil nitrogen loss in tropical farmland, causing many environmental issues. Biochar can improve soil quality and affect soil NH₃ volatilization. However, little is known about the effects of tropical crop residue biochar on soil NH₃ volatilization in tropical farmland. Therefore, a laboratory incubation study was conducted using four kinds of tropical crop residue biochar (pineapple straw (stem and leaves), banana straw, cassava straw and sugarcane bagasse pyrolyzed at 500 °C) with five addition rates (0.5%, 1%, 2%, 4%, and 6%) to evaluate their impact on NH₃ volatilization from tropical latosols. The results showed that NH₃ volatilization peaked twice under biochar application, once at 1-5 days and again at 12-16 days. The cumulative NH₃ volatilization (0.14-0.47 mg kg^-1) of the 20 biochar treatments was higher than that of the control (0.12 mg kg^-1). With the increase in the biochar addition rate, the soil pH, soil organic matter (SOM), urease activity, nitrate nitrogen content (NO₃^--N), nitrification rate and cumulative NH₃ volatilization increased gradually, and the 6% biochar treatment resulted in the highest NH₃ volatilization loss (0.19-0.47 mg kg^-1). The type of biochar is also a main factor affecting soil NH₃ volatilization. The cumulative NH₃ volatilization was the highest under pineapple straw biochar, as it was 19-43% higher than when the other three biochars were applied. However, sugarcane bagasse biochar had the lowest cumulative NH₃ volatilization due to its low quartz, sylvite and calcite contents, lack of -OH hydroxyl groups and high adsorbability. NH₃ volatilization was positively correlated with the soil pH, SOM, urease activity, NO₃^--N and nitrification rate. In conclusion, four tropical crop residue biochars can increase NH₃ volatilization in tropical latosols, so reducing NH₃ volatilization needs to be further considered in tropical crop residue biochar applications.

Climate change may interact with nitrogen fertilizer management leading to different ammonia loss in China's croplands

Despite research into the response of ammonia (NH₃ ) volatilization in farmland to various meteorological factors, the potential impact of future climate change on NH₃ volatilization is not fully understood. Based on a database consisting of 1063 observations across China, nonlinear NH₃  models considering crop type, meteorological, soil and management variables were established via four machine learning methods, including support vector machine, multi-layer perceptron, gradient boosting machine and random forest (RF). The RF model had the highest R² of 0.76 and the lowest RMSE of 0.82 kg NH₃ -N ha^-1 , showing the best simulation capability. Results of model importance indicated that NH₃ volatilization was mainly controlled by total input of N fertilizer, followed by meteorological factors, human managements and soil characteristics. The NH₃ emissions of China's cereal production (paddy rice, wheat and maize) in 2018 was estimated to be 3.3 Mt NH₃ -N. By 2050, NH₃ volatilization will increase by 23.1-32.0% under different climate change scenarios (Representative Concentration Pathways, RCPs), and climate change will have the greatest impact on NH₃ volatilization in the Yangtze river agro-region of China due to high warming effects. However, the potential increase in NH₃ volatilization under future climate change can be mitigated by 26.1-47.5% through various N fertilizer management optimization options.

Satellite-detected ammonia changes in the United States: Natural or anthropogenic impacts

Ammonia (NH3) is the most abundant alkaline component and can react with atmospheric acidic species to form aerosols that can lead to numerous environmental and health issues. Increasing atmospheric NH3 over agricultural regions in the US has been documented. However, spatiotemporal changes of NH3 concentrations over the entire US are still not thoroughly understood, and the factors that drive these changes remain unknown. Herein, we applied the Atmospheric Infrared Sounder (AIRS) monthly NH3 dataset to explore spatiotemporal changes in atmospheric NH3 and the empirical relationships with synthetic N fertilizer application, livestock manure production, and climate factors across the entire US at both regional and pixel levels from 2002 to 2016. We found that, in addition to the US Midwest, the Mid-South and Western regions also experienced striking increases in NH3 concentrations. NH3 released from livestock manure during warmer winters contributed to increased annual NH3 concentrations in the Western US. The influence of temperature on temporal evolution of NH3 concentrations was associated with synthetic N fertilizer use in the Northern Great Plains. With a strong positive impact of temperature on NH3 concentrations in the US Midwest, this region could possibly become an atmospheric NH3 hotspot in the context of future warming. Our study provides an essential scientific basis for US policy makers in developing mitigation strategies for agricultural NH3 emissions under future climate change scenarios.

The role of soils in the regulation of air quality

Soils play a key role in meeting the UN Sustainable Development Goals (SDGs). In this study, we review the contribution of soils to the regulation of air quality, which is one of 'Nature's Contributions to People' identified by the Intergovernmental-Policy Platform on Biodiversity and Ecosystem Services (IPBES). This is particularly relevant for SDG3 (health and well-being) and 11 (sustainable cities and well-being) but also impacts other SDGs. Soils can act as both a source and a sink of air pollutants (and their precursors). In addition, soils support plant growth which plays a major role in regulating air quality. The scale of the soil impacts on air quality range from global (e.g. greenhouse gas fluxes, stratospheric ozone depletion) to local (e.g. odours, particulates, pathogen transport). Harmful emissions from soil can be increased or decreased by anthropogenic activity, while climate change is likely to modify future emissions patterns, both directly and in response to human mitigation and adaption actions. Although soils are not the only source of these pollutants, it is worthwhile managing them to reduce erosion and nutrient losses to maintain soil health so we may continue to benefit from the contributions to good quality of life they provide. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People'.