National-scale spatial prediction of soil organic carbon and total nitrogen using long-term optical and microwave satellite observations in Google Earth Engine.

•Sentinel-1 utilization strategies greatly affected model outputs.•The models built by Sentinel-1 and Sentinel-2 performed similarly.•Models based on the fusion of Sentinel-1 and Sentinel-2 imagery improved mapping accuracy.•Models involving more years of satellite observations yielded more accurate predictions.•The GEE platform and the Sentinel satellites offer new opportunities for soil mapping.