Intensification of cropping systems improves crop productivity and soil organic carbon (SOC) storage by maintaining or enhancing existing SOC stocks. We compiled published data on SOC changes in agricultural soils globally from experiments evaluating the impact of bare-fallow reduction to determine the change in SOC storage that results from management change. Soil organic C storage under continuous and fallow-containing systems for each site was statistically compared. For the net change in SOC on a per area or on a per area and year basis, statistical differences among soil types, texture classes, climatic factors [mean annual precipitation (P), potential evapotranspiration (PET), and ratio of P/PET], and duration of the management change were determined.

A literature search was carried out using the Web of Science and Scopus databases. A broader search string was used as “(fallow) AND (soil organic carbon OR soil organic C OR SOC OR soil carbon OR soil C)”. With this search string, a total of 5834 entries were identified: 4486 from Web of Science and 1348 from Scopus. There are many terms used for fallow in the literature. Only “rotational fallow” as part of regular crop rotation tailors the requisite. Thus, replacement of fallow with growing a crop shorter than maturity, such as “cover crop” or “green manure,” is excluded. We had a few additional criteria, including duration of field studies for longer than four years; soil depth of 15 cm or deeper; experimental design in which the difference in SOC stocks can be estimated between continuous annual crop rotations and crop rotations with fallow; and studies estimating SOC stocks or reporting SOC concentration and soil bulk density so that the stocks could be estimated. Out of the 5384 articles identified in the search, there were 27 papers with 97 paired comparisons from Canada, 26 articles with 73 paired comparisons from the U.S.A., and 14 articles with 18 paired comparisons from other countries that met these criteria. A complete list of all studies with background information on citation, township, province/state, country, geo-coordinates, climatic properties (mean annual temperature, precipitation, and potential evapotranspiration), soil taxonomy, soil texture, crop rotations, replicate, tillage, fallow frequency, soil sampling depth, SOC stocks with fallow-based rotation and continuous cropping, net SOC stock change, and rate of SOC changes is provided here (Supporting Information SI Table 1).

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