A simplified systems-based screening framework for advancing nitrogen and phosphorus circularity in intensive agricultural regions

Context: The decoupling between crop and livestock production in intensive agri-food systems has disrupted ni
trogen and phosphorus cycles, increasing environmental pressures. Many studies have attempted to reconnect these 
sectors. However, most focus on the farm scale, analyze a single nutrient, or rely on complex modelling. Simpler, 
more accessible methods are needed to provide a holistic view at broader scales, such as the regional level.
Objective: This study develops a systems-based framework to identify nutrient hotspots and circularity oppor
tunities in intensive agri-food systems, using the Region of Murcia (Spain) as a case study.
Methods: The analysis relies primarily on regional official data, complemented by literature-derived parameters 
and assumptions. The system is structured into three subsystems: crops, animal production, and population. A 
simplified representation of nitrogen and phosphorus pathways was developed for the period 2020–2023.
Results and conclusions: Crop production was the main source of nutrient imbalance, with surpluses averaging 
39 kg N/ha year and 13 kg P/ha year. Animal excreta represented the main recoverable pool, substantially exceeding the amount of manure used in agriculture. The urban subsystem concentrated nutrients in sewage sludge and municipal solid waste, with approximately 42% of urban nitrogen and 58% of phosphorus ending up in landfills. These findings reveal circularity opportunities through a three-step screening-level prioritization: (i) correct crop production imbalances, (ii) contain and redirect livestock nutrients, and (iii) mobilize urban nutrient pools.
Significance: This approach offers a screening tool for prioritizing nutrient management interventions across 
intensive agricultural systems while using readily available data.