Impact of the Integration Level in Crop–Livestock Systems on Biomass Production, Nutrient Recycling, and Energy Efficiency

Sustainable agricultural practices are essential to address global food security challenges while minimizing environmental impacts. This study aimed to evaluate integrated farming systems with varying levels of integration (from lower to higher)—maize monoculture + livestock (MM), maize + cover crop + mixed prairie + livestock (MCP), and maize + red clover + mixed prairie + livestock (MRP)—to assess their contributions to circularity and sustainability. The research examined biomass and protein production, nutrient cycling, energy use, food needs covered, and workload over two cropping cycles. The findings revealed that highly integrated systems (MRP and MCP) significantly enhance biomass production, energy efficiency, and nutrient recycling compared to the MM system (p < 0.05). MRP produced 4 times more biomass than MM (9.4 t ha−1), while MCP achieved a 0.99 Nitrogen Recycling Index compared with 0.38 in MM, underscoring the benefits of grazing and increasing agrobiodiversity. Integrated systems also improved soil health (+17.4% organic matter in MRP and MCP, +91.5% nitrogen in MCP), reduced dependency on synthetic inputs, and boosted protein production (animal-derived protein in MRP and MCP = 395.4 kg, MM = 73.7 kg), thus meeting food needs for large populations. However, they required increased labor and technical expertise, presenting adoption barriers for smallholders. The synergy between agroecological practices and circularity offers a pathway to sustainable intensification, fostering economic, environmental, and social resilience. In this way, the results highlighted the potential of integrated farming systems to transform agricultural systems.