Nitrogen use efficiency in mixed crop-livestock systems: insights for sustainable intensification

Fabiana Pereyra-Goday^1*Jesus Castillo¹Pablo Rovira¹Walter Ayala¹Michael Lee²M. Jordana Rivero³

• ¹Instituto Nacional de Investigación Agropecuaria (INIA), Treinta y Tres, Uruguay
• ²Harper Adams University, Newport, Wales, United Kingdom
• ³Net Zero and Resilient Farming, Rothamsted Research,, North Wyke,, Devon, United Kingdom

The development of metrics to assess the sustainability of food production systems is vital for achieving sustainable global agri-food systems. Nitrogen use efficiency (NUE), defined as the ratio of nitrogen (N) in food outputs to total N inputs, is a key indicator of resource efficiency in crop and livestock systems. This study quantified and compared NUE, N surplus (NSURP, total N inputs minus N in food products), and N balance (N retained, calculated as inputs minus food outputs and losses) across four pasture-crop rotation systems with varying land-use intensity, evaluated at both component (crop and livestock) and system levels from 2019 to 2022. The systems included continuous cropping (CC), short rotation (SR; 2-year crops + 2-year pasture), long rotation (LR; 2year crops + 4-year pasture), and forage rotation (FR; continuous pasture with tall fescue). Data were primarily collected at the field level. Major findings showed crop NUE ranging from 62.5% (CC) to 83.8% (SR), livestock NUE from 5.5% (FR) to 24.4% (CC), and system NUE from 5.5% (FR) to 43.4% (CC). Systems with pastures (SR, LR, FR) retained more soil N (up to 64 kg N ha⁻¹ in FR) compared to CC (4.9 kg N ha⁻¹), highlighting the role of pastures in nutrient retention. These component-specific differences underscore the need for tailored management strategies, such as optimizing organic N inputs from livestock and improving grazing practices, to enhance NUE and guide systems toward a sustainable "safe operating space.