Livestock intensification in Argentina’s Pampas has reshaped feeding strategies and manure management, with major implications for nitrous oxide (N2O) emissions. Given its high global warming potential and direct link to nitrogen (N) excretion, understanding N2O dynamics is critical for climate-smart livestock production.
This study assessed how contrasting beef production systems-grazing versus feedlot-and their respective feeding strategies, particularly those including alfalfa, affect soil N2O emissions throughout the year.
A field experiment was conducted in 2020, applying urine and dung patches under both systems, each with two feeding regimes (with and without condensed tannins). Soil N2O emissions, moisture, temperature, inorganic N, and microbial communities were monitored throughout the year.
Diets with alfalfa and condensed tannins led to lower urinary N concentrations, but this did not always translate to reduced emissions. However, the grazing system, typically alfalfa-based pastures, showed significantly lower cumulative N2O emissions than the feedlot system. Estimated annual emission factors (EFs) from both urine and dung applications were lower than the default IPCC (2019) Tier 1 values, suggesting that local feeding strategies-especially those incorporating alfalfa-could substantially reduce emissions intensity.
Microbial community analyses revealed differences in composition between systems, yet only one taxon was positively correlated with higher N2O fluxes, reinforcing the complexity of microbial contributions to N cycling. These findings highlight the role of pasture-based systems and forage quality in modulating N dynamics and N2O emissions.
In conclusion, alfalfa-based grazing systems offer a promising strategy for reducing the environmental footprint of beef production, particularly in semi-arid regions. These findings contribute to a deeper understanding of how forage quality, production systems, and soil biology interact to shape the environmental footprint of livestock in semi-arid regions. They also highlight the importance of locally generated data for improving national greenhouse gas inventories.

Keywords: alfalfa, grazing systems, nitrous oxide, urine, dung, microbial communities, emission factors, climate-smart agriculture.