Impacts of dairy manure and synthetic fertilizers on greenhouse gas emissions and crop yields: A global meta-analytical comparison

Authors: BRAR, JAIVEER - Texas Agrilife Research; BAATH, GURJINDER - Texas Agrilife Research; JUNEJA, PULKIT - Texas Agrilife Research; JEONG, JAEHAK - Texas Agrilife Research; Krecker-Yost, Jenifer; Flynn, Kyle; WYATT, BRIANA - Texas Agrilife Research

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2025
Publication Date: 11/5/2025
Citation: Brar, J., Baath, G., Juneja, P., Jeong, J., Krecker-Yost, J.L., Flynn, K.C., Wyatt, B.M. 2025. Impacts of dairy manure and synthetic fertilizers on greenhouse gas emissions and crop yields: A global meta-analytical comparison. Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2025.180836.
DOI: https://doi.org/10.1016/j.scitotenv.2025.180836

Interpretive Summary: Farmers often use dairy manure as a natural fertilizer to improve soil health, but some worry that it might cause more pollution and lower crop yields compared to synthetic fertilizers. This is important because greenhouse gases like carbon dioxide, methane, and nitrous oxide contribute to climate change, and farmers need reliable ways to grow enough food. This study looked at how using dairy manure affects greenhouse gas emissions and crop growth compared to synthetic fertilizers. It considered different conditions like soil type, crop type, climate, and how the manure was applied. The researchers found that, in most cases, dairy manure didn’t cause more methane emissions or reduce grain yields compared to synthetic fertilizers. In fact, using composted manure helped crops grow better, and burying the manure in the soil reduced harmful gas emissions. This research shows that dairy manure can be a good alternative to synthetic fertilizers without increasing pollution or hurting crop production if farmers use the right methods for their specific conditions. This helps farmers make more sustainable choices, reducing their impact on climate change while still growing enough food.

Technical Abstract: Dairy manure (DM) is widely used as an organic nutrient source to enhance soil fertility, but concerns remain regarding its potential to increase greenhouse gas (GHG) emissions and reduce crop yields compared to synthetic fertilizers (SF). This global meta-analysis evaluated the effects of soil properties (texture, pH), nitrogen (N) application rate, crop type, water management, and climate zone on GHG emissions and crop yields under DM and SF applications. Additionally, we examined the impact of DM type and placement on GHG emissions and crop yield. Results showed no significant differences in methane (CH4) emissions and grain yield between DM and SF across most conditions. However, fine-textured soils exhibited higher carbon dioxide (CO2) emissions with DM application. Elevated CO2 emissions were also observed in alkaline soils (pH 7.4–7.6) when treated with DM, while slightly acidic soils (pH 5–6.5) favored higher crop yields. Lower DM application rates (=200 kg N ha'¹) reduced biomass and increased CO2 emissions, though grain yields remained comparable to SF. Crop-specific effects included higher nitrous oxide (N2O) emissions from barley (Hordeum vulgare L.) and lower corn (Zea Mays L.) yields under DM relative to SF. Greater CO2 emissions were associated with DM in cooler climates and under irrigation. Among DM types, liquid DM increased N2O emissions, whereas composted DM enhanced crop yields. Sub-surface DM application mitigated N2O emissions while maintaining yields. These findings indicate that DM can be effectively utilized without increasing GHG emissions or compromising crop yields compared to SF, provided that site-specific factors and trade-offs are carefully managed.