Nitrogen use efficiency of integrated crop-livestock systems at different levels of intensification

Development of metrics which evaluate sustainability of food production systems has become an important tool towards the realization of sustainable global agri-food systems. Nitrogen (N) use efficiency (food N outputs relative to all N inputs; NUE) is a key indicator of efficiency used in crop and livestock systems. The aim of this study was to quantify and compare the NUE, N surplus (NSURP, all N inputs minus N outputs in food products) and N balance/retained (all inputs minus N outputs and N losses) of four pasture crop rotations at different intensity at the component level (crop and livestock) for a period of 3 years (2019-2022). The systems evaluated were: continuous cropping (CC), short rotation (SR)- a 2 year (2-y) CC plus 2-y pasture, long rotation (LR) - a 2-y CC plus 4-y pasture, and forage rotation (FR), a continuous pasture with tall fescue. The information used in this study was predominately collected as primary data at the field level. Crop NUE values were: 62.5, 83.8 and 77.5% for CC, SR and LR, respectively. Livestock NUE was 24.4, 9.9, 14.3 and 5.5% for CC, SR, LR and FR, respectively. Our findings show differences between components and suggest the need to apply differential strategies to improve NUE, mainly in the livestock component, considering the relevance of developing sustainable food production systems.