More Like this

1. Net greenhouse gas balance in U.S. croplands: How can soils be part of the climate solution?

   https://doi.org/10.1111/gcb.17109  

   You, Yongfa; Tian, Hanqin; Pan, Shufen; Shi, Hao; Lu, Chaoqun; Batchelor, William D; Cheng, Bo; Hui, Dafeng; Kicklighter, David; Liang, Xin‐Zhong; et al (January 2024, Global Change Biology)

   Abstract Agricultural soils play a dual role in regulating the Earth's climate by releasing or sequestering carbon dioxide (CO₂) in soil organic carbon (SOC) and emitting non‐CO₂greenhouse gases (GHGs) such as nitrous oxide (N₂O) and methane (CH₄). To understand how agricultural soils can play a role in climate solutions requires a comprehensive assessment of net soil GHG balance (i.e., sum of SOC‐sequestered CO₂and non‐CO₂GHG emissions) and the underlying controls. Herein, we used a model‐data integration approach to understand and quantify how natural and anthropogenic factors have affected the magnitude and spatiotemporal variations of the net soil GHG balance in U.S. croplands during 1960–2018. Specifically, we used the dynamic land ecosystem model for regional simulations and used field observations of SOC sequestration rates and N₂O and CH₄emissions to calibrate, validate, and corroborate model simulations. Results show that U.S. agricultural soils sequestered Tg CO₂‐C year⁻¹in SOC (at a depth of 3.5 m) during 1960–2018 and emitted Tg N₂O‐N year⁻¹and Tg CH₄‐C year⁻¹, respectively. Based on the GWP100 metric (global warming potential on a 100‐year time horizon), the estimated national net GHG emission rate from agricultural soils was Tg CO₂‐eq year⁻¹, with the largest contribution from N₂O emissions. The sequestered SOC offset ~28% of the climate‐warming effects resulting from non‐CO₂GHG emissions, and this offsetting effect increased over time. Increased nitrogen fertilizer use was the dominant factor contributing to the increase in net GHG emissions during 1960–2018, explaining ~47% of total changes. In contrast, reduced cropland area, the adoption of agricultural conservation practices (e.g., reduced tillage), and rising atmospheric CO₂levels attenuated net GHG emissions from U.S. croplands. Improving management practices to mitigate N₂O emissions represents the biggest opportunity for achieving net‐zero emissions in U.S. croplands. Our study highlights the importance of concurrently quantifying SOC‐sequestered CO₂and non‐CO₂GHG emissions for developing effective agricultural climate change mitigation measures. 

   more » « less
2. Preferential Emission of Microplastics from Biosolid-Applied Agricultural Soils: Field Evidence and Theoretical Framework

   https://doi.org/10.1021/acs.estlett.3c00850  

   Leonard, Jamie; Ravi, Sujith; Mohanty, Sanjay K (February 2024, Environmental Science & Technology Letters)

   Land application of wastewater biosolids on agricultural soils is suggested as a sustainable pathway to support the circular economy; however, this practice often enriches microplastics and associated contaminants in topsoil. Wind could transport these contaminated microplastics, thereby increasing their inhalation health risks. Analyzing wind-borne sediments collected from wind tunnel experiments on biosolid-applied agricultural fields, we show enrichment of microplastics in wind-blown sediments. We explain this preferential transport and enrichment of microplastics by using a theoretical framework. This framework reveals how the combined effects of the low density of microplastics and weakened wet-bonding interparticle forces between microplastics and soil particles lower their threshold velocity, the minimum wind velocity necessary for wind erosion to occur. Our calculations indicate that microplastics could be emitted at wind speeds lower than the characteristic threshold of background soil. Analyzing the windspeed distribution for 3 months of wind events over a bare soil surface, we showed that more than 84% of the wind events exceed the threshold velocity of microplastics of size 150 μm, while only 23% of the wind events exceed the threshold velocity of the background soil. Thus, current models for fugitive dust emissions may underestimate the microplastic emission potential of biosolid-amended soils. 

   more » « less
3. Life cycle greenhouse gas emissions for irrigated corn production in the U.S. great plains

   https://doi.org/10.1016/j.envc.2023.100750  

   Koushki, Raana; Sharma, Sumit; Warren, Jason; Foltz, Mary E. (December 2023, Environmental Challenges)

   Agricultural management practices improve crop yields to satisfy food demand of the growing population. However, these activities can have negative consequences, including the release of greenhouse gas (GHG) emissions that contribute to global climate change. To mitigate this global environmental problem, the management practices that contribute the most to system GHG emissions should be identified and targeted to mitigate emissions. Accordingly, we estimated the cradle-to-product GHG emissions of irrigated corn production under various farmer-selected scenarios at an experimental testing field in the semi-arid U.S. Great Plains. We applied a carbon footprint approach to quantify life cycle GHG emissions associated with pre-field (e.g., energy production, fertilizer production) and in-field (e.g., groundwater pumping, fertilizer application) activities within fourteen scenarios in the 2020 Oklahoma Testing Ag Performance Solutions (TAPS) sprinkler corn competition. We determined that 63% of the total GHG emission from corn production was associated with in- field activities and that agricultural soil emissions were the overall driving factor. Soil biochemical processes within agricultural soils were expected to contribute an average of 89 ± 18 g CO2-eq kg− 1 corn of the total 271 ± 46 g CO2-eq kg− 1 corn estimated from these systems. On-site natural gas combustion for agricultural groundwater pumping, pre-field fertilizer production, and pre-field energy production for groundwater pumping were the next most influential parameters on total GHG emissions. Diesel fuel, seed, and herbicide production had insignificant contributions to total GHG emissions from corn production. The model was most sensitive to the modeled GHG emissions from agricultural soil, which had significant uncertainty in the emission factor. Therefore, future efforts should target field measurements to better predict the contribution of direct soil emissions to total GHG emissions, particularly under different managements. In addition, identifying the optimal application rate of irrigation water and fertilizer will help to decrease GHG emissions from groundwater irrigated crops. 

   more » « less
4. Elevated temperature and nutrients lead to increased N2O emissions from salt marsh soils from cold and warm climates

   https://doi.org/10.1007/s10533-023-01104-0  

   Comer-Warner, Sophie A.; Ullah, Sami; Dey, Arunabha; Stagg, Camille L.; Elsey-Quirk, Tracy; Swarzenski, Christopher M.; Sgouridis, Fotis; Krause, Stefan; Chmura, Gail L. (January 2024, Biogeochemistry)

   Abstract Salt marshes can attenuate nutrient pollution and store large amounts of ‘blue carbon’ in their soils, however, the value of sequestered carbon may be partially offset by nitrous oxide (N₂O) emissions. Global climate and land use changes result in higher temperatures and inputs of reactive nitrogen (Nr) into coastal zones. Here, we investigated the combined effects of elevated temperature (ambient + 5℃) and Nr (double ambient concentrations) on nitrogen processing in marsh soils from two climatic regions (Quebec, Canada and Louisiana, U.S.) with two vegetation types,Sporobolus alterniflorus(= Spartina alterniflora) andSporobolus pumilus(= Spartina patens), using 24-h laboratory incubation experiments. Potential N₂O fluxes increased from minor sinks to major sources following elevated treatments across all four marsh sites. One day of potential N₂O emissions under elevated treatments (representing either long-term sea surface warming or short-term ocean heatwaves effects on coastal marsh soil temperatures alongside pulses of N loading) offset 15–60% of the potential annual ambient N₂O sink, depending on marsh site and vegetation type. Rates of potential denitrification were generally higher in high latitude than in low latitude marsh soils under ambient treatments, with low ratios of N₂O:N₂indicating complete denitrification in high latitude marsh soils. Under elevated temperature and Nr treatments, potential denitrification was lower in high latitude soil but higher in low latitude soil as compared to ambient conditions, with incomplete denitrification observed except in LouisianaS. pumilus. Overall, our findings suggest that a combined increase in temperature and Nr has the potential to reduce salt marsh greenhouse gas (GHG) sinks under future global change scenarios. 

   more » « less
5. Balancing Non‐CO ₂ GHG Emissions and Soil Carbon Change in U.S. Rice Paddies: A Retrospective Meta‐Analysis and Agricultural Modeling Study

   https://doi.org/10.1029/2023AV001052  

   Zhang, Jingting; Tian, Hanqin; You, Yongfa; Liang, Xin‐Zhong; Ouyang, Zutao; Pan, Naiqing; Pan, Shufen (February 2024, AGU Advances)

   Abstract U.S. rice paddies, critical for food security, are increasingly contributing to non‐CO₂greenhouse gas (GHG) emissions like methane (CH₄) and nitrous oxide (N₂O). Yet, the full assessment of GHG balance, considering trade‐offs between soil organic carbon (SOC) change and non‐CO₂GHG emissions, is lacking. Integrating an improved agroecosystem model with a meta‐analysis of multiple field studies, we found that U.S. rice paddies were the rapidly growing net GHG emission sources, increased 138% from 3.7 ± 1.2 Tg CO₂eq yr⁻¹in the 1960s to 8.9 ± 2.7 Tg CO₂eq yr⁻¹in the 2010s. CH₄, as the primary contributor, accounted for 10.1 ± 2.3 Tg CO₂eq yr⁻¹in the 2010s, alongside a notable rise in N₂O emissions by 0.21 ± 0.03 Tg CO₂eq yr⁻¹. SOC change could offset 14.0% (1.45 ± 0.46 Tg CO₂eq yr⁻¹) of the climate‐warming effects of soil non‐CO₂GHG emissions in the 2010s. This escalation in net GHG emissions is linked to intensified land use, increased atmospheric CO₂, higher synthetic nitrogen fertilizer and manure application, and climate change. However, no/reduced tillage and non‐continuous irrigation could reduce net soil GHG emissions by approximately 10% and non‐CO₂GHG emissions by about 39%, respectively. Despite the rise in net GHG emissions, the cost of achieving higher rice yields has decreased over time, with an average of 0.84 ± 0.18 kg CO₂eq ha⁻¹emitted per kilogram of rice produced in the 2010s. The study suggests the potential for significant GHG emission reductions to achieve climate‐friendly rice production in the U.S. through optimizing the ratio of synthetic N to manure fertilizer, reducing tillage, and implementing intermittent irrigation. 

   more » « less