Soil database: https://files.isric.org/

Soil Maps for africa: https://www.isda-africa.com/isdasoil/isdasoil-on-aws/

erosion maps: https://esdac.jrc.ec.europa.eu/themes/global-soil-erosion

Another soil: database https://files.isric.org/public/other/

A series of interesting maps including soils: https://earthmap.org/

And for free remote sensing data I recommend the use of the Google Earth Engine.

In addition to the links provided by Jaime Garbanzo León , you can also download the HWSD soil data viewer

https://www.fao.org/soils-portal/data-hub/soil-maps-and-databases/harmonized-world-soil-database-v12/en/

http://webarchive.iiasa.ac.at/Research/LUC/External-World-soil-database/HTML/index.html?sb=1

There are a number of great resources to help you learn about using GIS and Remote Sensing for soil ecological studies. Here are a few:

1. ESRI's Introduction to GIS for Soil Science: https://www.esri.com/en-us/training/catalog/introduction-to-gis-for-soil-science

2. GIS and Remote Sensing for Soil Science by Robert Pouyat and Edward T. Elliott: https://www.amazon.com/GIS-Remote-Sensing-Soil-Science/dp/1566706663

3. USGS Soil Survey GIS Resources: https://www.usgs.gov/core-science-systems/ngp/soils/ssurgo/gis

4. University of California's GIS for Soil Science tutorial: http://www.scottsdalefarm.org/gis-tutorial/gis-soil-science/

5. USDA's GIS Soil Resources: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/geography/gis/

6. GIS in Soil Science: A Practical Guide by M.A. Jansen and J.W. Leenaars: https://www.amazon.com/GIS-Soil-Science-Practical-Guide/dp/1402050668