iSDAsoil: soil extractable Calcium for Africa predicted at 30 m resolution at 0-20 and 20-50 cm depths

iSDAsoil dataset soil extractable Calcium 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. et al. African soil properties and nutrients mapped at 30 m spatial resolution using two-scale ensemble machine learning. Sci Rep 11, 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 Cloud-Optimized GeoTIFF version.

Layer description:

sol_log.ca_mehlich3_m_30m_*..*cm_2001..2017_v0.13_wgs84.tif = predicted soil extractable Calcium mean value,

sol_log.ca_mehlich3_md_30m_*..*cm_2001..2017_v0.13_wgs84.tif = predicted soil extractable Calcium 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:

Variable: log.ca_mehlich3
R-square: 0.84
Fitted values sd: 1.24
RMSE: 0.543

Random forest model:
Call:
stats::lm(formula = f, data = d)

Residuals:
Min 1Q Median 3Q Max
-6.0376 -0.2577 0.0076 0.2756 5.3825

Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 5.737959 3.850998 1.490 0.136
regr.ranger 1.054018 0.003175 331.978 < 2e-16 ***
regr.xgboost -0.030930 0.003939 -7.853 4.1e-15 ***
regr.cubist 0.061829 0.003561 17.364 < 2e-16 ***
regr.nnet -0.855297 0.561006 -1.525 0.127
regr.cvglmnet -0.065040 0.003225 -20.166 < 2e-16 ***
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5428 on 144593 degrees of freedom
Multiple R-squared: 0.8403, Adjusted R-squared: 0.8402
F-statistic: 1.521e+05 on 5 and 144593 DF, p-value: < 2.2e-16

To back-transform values (y) to ppm use the following formula:

ppm = expm1( y / 10 )

To submit an issue or request support please visit https://isda-africa.com/isdasoil