Biogeochemistry 1 Biological materials 1 China 1 Digital soil mapping 1 Digital soil mappings 1 Guangdong 1 Mapping 1 Model method 1 Model samples Modelling method 1 Optimal combination 1 Organic compounds 1 Probability distributions 1 Probability: distributions 1 Sample size 1 Sample sizes 1 Sampling 1 Small Sample Size 1 Soil organic matter 1 Soil organic matters 1 Soil sample 1 Soil surveys 1 Soils 1 Spatial informations 1 accuracy assessment 1 comparative study 1 digital mapping 1 optimization 1 probability 1 sampling 1