Strategies to reduce N waste through crop and livestock reconnection

The increasing specialization of territories into either crop or livestock production systems over recent decades has led to disconnected agricultural systems. This decoupling can compromise nitrogen (N) recirculation, leading to N losses and inefficiencies that become evident at the territorial scale. Reconnecting crop and livestock systems within a region can be a powerful strategy to reduce N waste, enhance self-sufficiency, and shield farmers from geopolitical disruptions and price shocks. This paper has two general aims: 1) examine representative cases of crop–livestock disconnection across diverse highly productive regions of the world, and (2) summarize and critically evaluate the key insights from the papers published in the Special Issue “Reducing nitrogen waste through crop and livestock reconnection”, gathering strategies to reduce N waste through crop and livestock reconnection. N budgets in agricultural systems considering crop and livestock production, fertilizer and feed use and trade are analysed for provinces and counties in Spain, France, USA, China and Europe. Further information was collected from literature published in this Special Issue and beyond. The literature was analysed to gather a set of reconnection strategies aimed at reducing N waste, that have been tried and tested in agricultural systems around the world. A marked farm specialization observed in counties, provinces, and regions across Europe, China, and the USA has led to more linear N flows, increased external dependence on synthetic fertilizers and imported feed, and inefficient manure redistribution. The nineteen papers from in 4 continents and 14 countries provided diverse strategies to reduce N waste through crop and livestock reconnection by: 1) improving manure allocation (15 cases), 2) relocating feed production (11 cases) and 3) promoting specific spatial planning in the territory (5 cases). We conclude that implementing circular N use can reduce N waste in many regions. However, the most promising strategies must be tailored to the specific characteristics of each area. This requires a comprehensive assessment of livestock densities and feed compositions, potential crop combinations, climate conditions, and environmental vulnerabilities. We also identified several limitations, challenges and technical, economic, social, governance, and structural barriers associated with these strategies. Key limitations are related to nutrient saturation in soils, excessively high livestock densities in certain areas, and the substantial level of coordination required for effective implementation. Reconnecting crops and livestock beyond individual farms is challenging but offers major benefits: less N waste, lower external dependence, and better circularity for sustainable agriculture. Still, it is not a cure-all; extra measures are needed in highly intensive regions. • Crop and livestock disconnection results in nitrogen waste. • Disconnection examples are analized in USA, China and Europe. • Solutions include manure management, feed relocation and spatial planning. • Nineteen contributions provide successful cases of reconnection worldwide. • Reconnection alone cannot solve all nitrogen waste problems.