Countrywide mapping and assessment of organic carbon saturation in the topsoil using machine learning-based pedotransfer function with uncertainty propagation

•It was assumed that soils covered by forest can be considered as saturated in SOC.•Cubist-based PTF was developed for predicting and mapping saturated SOC content.•Environmental conditions are also important factors in predicting SOC saturation.•Significant SOC deficit was revealed on large part of Hungary with high variability.•Highest SOC deficits occur in areas with medium to high SOC content.