Rosemery Alesandra Firmino dos Santos1, 2*, Júnior Melo Damian3, María Almagro4, Rafael Silva Santos5, Leidivan Almeida Frazão6, 7, Dener Márcio da Silva Oliveira8, Maurício Roberto Cherubin1, 7, Carlos Eduardo Pellegrino Cerri1, 7
1 Department of Soil Science, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba, SP, Brazil
2 Fellow of the National Institute of Science and Technology for Low Carbon Agriculture (INCT-ABC/CNPq), Porto Alegre, RS, Brazil
3 Embrapa Agricultura Digital, Campinas, SP, Brazil
4 Institute of Agricultural and Fisheries Research and Training (IFAPA), Camino de Purchil Centre, Granada, Spain
5 Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, United States
6 Universidade Federal de Minas Gerais, Montes Claros, MG, Brazil
7 Center for Carbon Research in Tropical Agriculture (CCARBON), University of São Paulo, Piracicaba, SP, Brazil
8 Institute of Agricultural Sciences, Federal University of Viçosa, Florestal, MG, Brazil
2 Fellow of the National Institute of Science and Technology for Low Carbon Agriculture (INCT-ABC/CNPq), Porto Alegre, RS, Brazil
3 Embrapa Agricultura Digital, Campinas, SP, Brazil
4 Institute of Agricultural and Fisheries Research and Training (IFAPA), Camino de Purchil Centre, Granada, Spain
5 Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, United States
6 Universidade Federal de Minas Gerais, Montes Claros, MG, Brazil
7 Center for Carbon Research in Tropical Agriculture (CCARBON), University of São Paulo, Piracicaba, SP, Brazil
8 Institute of Agricultural Sciences, Federal University of Viçosa, Florestal, MG, Brazil
Abstract
Soil is a multifunctional sustainable pillar that holds the Earth by connecting and supporting the lithosphere, biosphere, hydrosphere, atmosphere, and anthroposphere. Circular economy (CE) has emerged as a solution to human-environmental sustainability needs. CE implementations have been popularized across various fields including engineering, agriculture, forestry, and waste management, but comprehensive studies focusing mainly on soil circularity in scientific literature are unavailable. This paper aims to outline the conceptual frameworks underpinning soil functions, services, and threats in relation to CE. This is done by identifying and mapping the research trajectory, thematic chronology, and evolution of the concept of CE and soil from contemporary scientific literature. The conceptual network is categorized into six main clusters (viz; extraction and processing, nutrient cycling, ecosystem services, contamination, waste management, and soil-related technologies) which were assessed by applying recycling, regeneration, and repurpose strategies in the soil context. Mapping the triple-R to soil functions, our study revealed that nutrient cycling was the most published topic on CE and soil. Further, we observed that research on recycling had the most attention and increased rapidly, regeneration increased marginally, while repurpose decreased. The study concludes that thematic conceptualization based on the triple-R is neither definite nor comprehensive but is meant to be indicative and applicable considering the “triple-A (agent-action-aim) principle representing intention, action, and purpose. A comprehensive knowledge synthesis about circular soil principles could help in the application of decisive, operational, and competitive benefits, vis-à-vis fostering more studies to intensify and promote soil circularity for a better society.Brazilian livestock production is predominantly based on pastures, characterized by extensive management and low forage productivity. To increase forage and livestock productivity while enhancing soil carbon storage, the use of more productive pastures and the diversification of production systems have been proposed. Integrated systems, such as crop-livestock (ICL) and crop-livestock-forest (ICLF) systems, are widely recommended to achieve these goals. In this review, we synthesize studies comparing permanent pastures and integrated systems, with and without a tree, that applied physical fractionation of soil organic matter. Our objective was to assess the capacity of integrated systems to store soil carbon relative to pastures and to provide insights for farmers, policymakers, and future research. The reviewed studies reaffirm the role of pastures as soil carbon sinks, primarily because they stabilize carbon in mineral-associated organic matter (MAOM), the largest and most persistent soil carbon pool. We found that grazing management and soil fertility in the pasture strongly control the capacity of both integrated and non-integrated systems to store soil carbon, due to the role of grasses in promoting MAOM formation. Integrated systems also have the potential to increase particulate organic matter (POM), mainly through greater crop diversification; however, increases in soil carbon are dependent on its transformation into MAOM. Integrated livestock-forest systems tend to behave similarly to permanent pastures, whereas crop-livestock systems exhibit more dynamic organic matter turnover. In tree-based systems, soil carbon storage depends on the proportion and management of the pasture component, while in systems without trees, soil carbon stabilization is strongly controlled by pasture management, especially nitrogen availability and grazing intensity. This review highlights the importance of distinguishing integrated systems with a tree component from those without trees, as they differ in their effects on soil carbon dynamics. The use of soil organic matter physical fractions is a key approach for understanding soil carbon storage in these systems. However, further studies are needed, particularly in systems designed for pasture recovery and livestock productivity, to better assess their potential to enhance soil carbon storage.