Soil Organic Carbon and Nitrogen in Mediterranean Soils: A Systematic Mapping of Research from 1958 to 2025

Soil organic carbon (SOC) and nitrogen (N) are key indicators of soil quality, ecosystem functioning, and climate change mitigation in Mediterranean environments, which are particularly vulnerable to land degradation and climate variability. Despite extensive research efforts, evidence on SOC and N in Mediterranean soils remains fragmented across regions, land uses, and methodological approaches. 

This study presents a systematic map of international research on SOC and N in the Mediterranean Basin published between 1958 and 2025, with the objective of identifying research trends, thematic emphases, and knowledge gaps. A comprehensive literature search was conducted using Scopus and Web of Science databases. Search strings were developed iteratively using Boolean operators to maximize coverage of soil traits, soil management, land use, and soil quality, combined with geographic keywords representing Mediterranean countries and regions. All retrieved records were exported, merged, and screened after duplicates were removed. Study selection was carried out collaboratively by members of the SHARInG-MeD consortium, following predefined inclusion and exclusion criteria aligned with the project objectives.

A total of 60,822 records were retrieved. After removal of 16,553 duplicates (37.4%), 44,269 publications were screened. Of these, 18,012 studies (41%) met the objectives of the SHARInG-MeD project, and 5,373 publications specifically addressed soil organic carbon and nitrogen and were included in this systematic map. The mapped literature shows a strong temporal increase in SOC and N research since 1958, with pronounced geographical imbalances favoring northern Mediterranean countries. Agricultural land use, soil management practices, and land-use change emerged as dominant research themes, while long-term experiments, paired-site approaches, and harmonized analytical methodologies remain underrepresented.

This systematic map represents the most comprehensive synthesis to date of SOC and nitrogen research in Mediterranean soils and provides a robust evidence base for future meta-analyses, methodological harmonization, and evidence-based soil management and policy development at the Mediterranean scale.

Funding : The present work was funded by the research and innovation action “Soil Health and Agriculture Resilience through an Integrated Geographical information systems of Mediterranean Drylands” (SHARInG-MeD) funded by the “Partnership for Research & Innovation in the Mediterranean Area” (PRIMA Foundation) under the grant agreement number 2211.