Biogeochemistry 6 Organic compounds 6 Soils 6 soil organic matter Biological materials 4 Soil surveys 4 China 3 Soil organic matters 3 accuracy assessment 3 Decision trees 2 Digital soil mappings 2 Ecosystems 2 Forestry 2 Interpolation 2 Machine learning 2 Nutrients 2 Probability distributions 2 Random forest 2 Random forests 2 Soil fertility 2 Soil organic matter 2 Soil organic matter contents 2 machine learning 2 probability 2 soil fertility 2 Above-ground plant cover 1 Acer truncatum 1 Agriculture 1 Ailanthus altissima 1 Alkalinity 1