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. 2020 Jul 2;10:10851. doi: 10.1038/s41598-020-67467-8

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fertility over time. The three different phases in the cycle of cultivation represented by fields N1 (two weeks after addition of fresh biomass to rehabilitate a field that had been left fallow for at least 10 years), N2 (one year after rehabilitation, field age > 40 years), and N3 (fallow, since about 10 years). Some fields are not only left fallow, but abandoned (AF, abandoned at least 20 years ago). Peak of chemical fertility in the layers where crop roots are concentrated is reached some months to one year after rehabilitation for cultivation (“Fertility Window”). Fertility then declines, returning to values typical of nearby uncultivated soils during the fallow period and falling even lower with abandonment. Plots show downprofile colour (visualized by conversion of spectrophotometrically measured colour space values into the RGB colour space³⁹ and chemical analysis of the main profiles (X) of fields N1, N2, and N3. Dashed lines in the background are the mean values for each chemical parameter of the topsoil (Ah) samples taken at 10 cm depth from areas near each field in the RFSA. (Graphs were plotted with Grapher and arranged using Adobe Illustrator).