Total nitrogen China 6 Soils 6 Organic carbon 4 Water quality 4 Decision trees 3 Lakes 3 Land use 3 Nutrients 3 Runoff 3 Soil surveys 3 machine learning 3 soil organic matter 3 water quality 3 Agriculture 2 Biogeochemistry 2 Biomass 2 Conservation measures 2 Effluents 2 Eutrophication 2 Forecasting 2 Least squares approximations 2 Loss rates 2 Machine learning 2 Nitrogen 2 Random forests 2 Rivers 2 Runoff plot 2 Runoff plots 2 Sewage pumping plants 2