DOI: 10.5281/zenodo.4090374
title: iSDAsoil: soil extractable Magnesium for Africa predicted at 30 m resolution at 0-20 and 20-50 cm depths

description: iSDAsoil dataset soil extractable Magnesium (Mg) log-transformed predicted at 30 m resolution for 0–20 and 20–50 cm depth intervals. Data has been projected in WGS84 coordinate system and compiled as COG. Predictions have been generated using multi-scale Ensemble Machine Learning with 250 m (MODIS, PROBA-V, climatic variables and similar) and 30 m (DTM derivatives, Landsat, Sentinel-2 and similar) resolution covariates. For model training we use a pan-African compilations of soil samples and profiles (iSDA points, AfSPDB, and other national and regional soil datasets). Cite as: Hengl, T., Miller, M.A.E., Križan, J. <em>et al.</em> African soil properties and nutrients mapped at 30 m spatial resolution using two-scale ensemble machine learning. <em>Sci Rep</em> <strong>11, </strong>6130 (2021). https://doi.org/10.1038/s41598-021-85639-y To open the maps in QGIS and/or directly compute with them, please use the <strong>Cloud-Optimized GeoTIFF version</strong>. Layer description: sol_log.mg_mehlich3_m_30m_*..*cm_2001..2017_v0.13_wgs84.tif = predicted soil extractable Magnesium mean value, sol_log.mg_mehlich3_md_30m_*..*cm_2001..2017_v0.13_wgs84.tif = predicted soil extractable Magnesium model (prediction) errors, Model errors were derived using bootstrapping: md is derived as standard deviation of individual learners from 5-fold cross-validation (using spatial blocking). The model 5-fold cross-validation (mlr::makeStackedLearner) for this variable indicates: <pre><code>Variable: log.mg_mehlich3 R-square: 0.815 Fitted values sd: 1.05 RMSE: 0.498 Random forest model: Call: stats::lm(formula = f, data = d) Residuals: Min 1Q Median 3Q Max -5.8775 -0.2312 0.0028 0.2465 3.7400 Coefficients: Estimate Std. Error t value Pr(&gt;|t|) (Intercept) -0.034349 0.051219 -0.671 0.5025 regr.ranger 1.034217 0.003263 316.950 &lt;2e-16 *** regr.xgboost -0.008057 0.003854 -2.091 0.0366 * regr.cubist 0.073223 0.003649 20.067 &lt;2e-16 *** regr.nnet -0.017388 0.009528 -1.825 0.0680 . regr.cvglmnet -0.075566 0.003402 -22.213 &lt;2e-16 *** --- Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 Residual standard error: 0.4979 on 136681 degrees of freedom Multiple R-squared: 0.8152, Adjusted R-squared: 0.8152 F-statistic: 1.206e+05 on 5 and 136681 DF, p-value: &lt; 2.2e-16 </code></pre> To back-transform values (y) to ppm use the following formula: <pre><code>ppm = expm1( y / 10 )</code></pre> To submit an issue or request support please visit <strong>https://isda-africa.com/isdasoil</strong>
description: iSDA is a social enterprise founded by – Rothamsted Research, the World Agroforestry (ICRAF) and the International Institute of Tropical Agriculture (IITA) – building on the legacy of the AfSIS project to create financially sustainable agronomy solutions for smallholder farmers. We are grateful to all national soil agencies especially GhaSIS, TanSIS, EthioSIS and NiSIS for providing soil sampling data and technical support.
description: {"references": ["Hengl, T., Leenaars, J. G., Shepherd, K. D., Walsh, M. G., Heuvelink, G. B., Mamo, T., ... & Wheeler, I. (2017). Soil nutrient maps of Sub-Saharan Africa: assessment of soil nutrient content at 250 m spatial resolution using machine learning. Nutrient Cycling in Agroecosystems, 109(1), 77-102.", "Hengl, T., MacMillan, R.A., (2019). Predictive Soil Mapping with R. OpenGeoHub foundation, Wageningen, the Netherlands, 370 pages, www.soilmapper.org, ISBN: 978-0-359-30635-0.", "Leenaars, J. G. B. (2014). Africa Soil Profiles Database, Version 1.2. A compilation of georeferenced and standardised legacy soil profile data for Sub-Saharan Africa (with dataset). Africa Soil Information Service (AfSIS) project (No. 2014/03). ISRIC-World Soil Information.", "V\u00e5gen, T. G., Winowiecki, L. A., Tondoh, J. E., Desta, L. T., & Gumbricht, T. (2016). Mapping of soil properties and land degradation risk in Africa using MODIS reflectance. Geoderma, 263, 216-225."]}