What are the effects of agricultural management on soil organic carbon in boreo-temperate systems?

Background: Soils contain the largest stock of organic carbon (C) in terrestrial ecosystems and changes in soil C
stocks may significantly affect atmospheric CO2. A significant part of soil C is present in cultivated soils that occupy
about 35 % of the global land surface. Agricultural intensification has led to practices that may decrease soil organic
carbon (SOC), and agricultural management has the potential to be a powerful tool for climate change mitigation
and increased soil fertility through SOC sequestration. Here, we systematically map evidence relating to the impacts
of agricultural management on SOC in arable systems of the warm temperate and snow climate zones (subset of
temperate and continental climates: Köppen–Geiger Classification).
Methods: Seventeen academic citation databases, 3 search engines and 25 organisational websites were searched
for literature (academic and grey) using search strings translated into a range of languages relevant to the included
geographical scope of the topic. Stakeholders were also contacted with requests for evidence. Bibliographic checking
of 127 relevant reviews was undertaken to check for missing articles. Screening for relevance against predefined inclusion
criteria was undertaken at title, abstract and full text levels according to a published protocol. All relevant studies
were coded in a meta-database describing the citation, study settings, methods and quantitative data available (without
extraction of the study findings). A basic critical appraisal of included studies was also performed. A geographical
information system (GIS) presenting the map database on a physical, online map was also produced.
Results: A total of 735 studies from 553 articles was included in the systematic map database. Studies investigated
one or more of five broad categories of interventions: amendments (286 studies), crop rotations (238), fertilisers (307),
tillage (306), and multiple interventions (55). Studies were identified from across the includible climate zones, with the
notable underrepresentation from Russia. The majority of studies employed only point sampling of SOC, low levels
of true spatial replication and moderate study periods (i.e. 10–20 years). Missing key methodological information was
found in 28 % of studies.
Conclusions: Long-term study sites identified in this map provide a useful addition to existing databases of longterm
experiments (LTEs). The identification of knowledge gaps, such as studies from Russia, also identify a need for
improved cataloguing or reporting of existing and on-going research. This systematic map database represents a useful
resource for decision-makers wishing to identify knowledge gaps warranting further primary research, knowledge
gluts warranting further secondary research, and deficiencies and best practice in research methodology. In addition
to the systematic map database, we have also produced two further resources: (1) a database of LTE sites investigating
agricultural management and SOC, and (2) a database of reviews and meta-analyses. To our knowledge, this is the first systematic review or map that utilises a GIS for presentation of an evidence base, which we believe substantially increases the utility of the map outputs.