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The rise in human population and the advent of biological wastewater treatment has led to increased biosolid production, which requires sustainable solutions to mitigate potential negative impacts associated with the disposal of biosolids. Biosolid land application has the potential to decrease reliance on synthetic fertilizers and improve soil fertility; however, the microbial activity and associated greenhouse gas (GHG) emissions need to be evaluated to ensure there are no negative externalities of this approach. To address these issues, this study aimed to (i) assess the potential of a biosolid-amended soil system to emit nitrous oxide (N₂O), (ii) quantify actual field GHG emissions from biosolid-amended soils, and (iii) evaluate a process-based model to predict these soil GHG emissions. This study performed a comprehensive analysis, including laboratory (potential assays and gene abundances), field (static chamber GHG measurements), and modeling (process-based) approaches, to understand the effect of biosolids on soil GHG emissions. We found that biosolid application increased soil nitrate and organic matter, and decreased soil pH in the short-term. Together, the changes in soil conditions promoted more denitrification, which became more complete with laboratory potential dinitrogen higher than nitrous oxide as the end-product over time. In the field, GHG emissions were generally higher in biosolid-amended soils, particularly just after biosolid application. While the predictive model was able to simulate general trends for field GHG emissions, it often underpredicted the magnitude of these emissions. Overall, despite initial increases in GHG, biosolids have the potential as a sustainable amendment to improve soil health and mitigate GHG emissions in agricultural practices over the long term. This research contributes to understanding biosolid use in promoting environmental sustainability and offers insights for future agricultural management strategies. 

Nitrous oxide (N₂O) is a potent greenhouse gas that contributes to stratospheric ozone depletion and global climate change. Soil denitrification has two potential end-products, N₂O and dinitrogen (N₂), and the ratio of these end-products (N₂O:(N₂O+N₂) or the N₂O ratio) is controlled by various factors. This study aims to quantify the influence of soil pH on the ratio of denitrification end-products in Oklahoma soils with different soil textures. Six natural grassland soils encompassing three distinct soil textures were incubated in the laboratory under natural and modified pH with an overall tested pH ranging from 2 to 10. Denitrification end-products were measured in the laboratory using the acetylene inhibition technique and further estimated using a process-based biogeochemical model. Both the laboratory and model results showed that soil pH and texture influenced the ratio of the denitrification end-products. Generally, as soil pH increased the N₂O ratio decreased, although both lab and model results indicated that this relationship was not linear. Soil texture may have an indirect effect on the N₂O ratio, as two soils of the same texture could have different N₂O ratios. However, clay percentage of the soil did show a linear positive correlation with the N₂O ratio, suggesting components of soil texture may be more influential than others. Overall, soil pH was a controlling factor in the ratio of denitrification end-products and the newly observed nonlinear relationship warrants further study, particularly when considering its effects in different soil textures. 

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.