Empirically-derived pedotransfer functions for predicting bulk density in European soils

The lack of comprehensive data on the bulk density of soil types at the European scale is a serious limitation for pan-European environmental risk assessment studies. Although many predictive methods have been published, most have limitations for application across Europe. We therefore developed a semi-empirical method of prediction using a large UK dataset and tested it and some other methods against a pan-European dataset. Our method indicated that five separate conceptual groupings of the development dataset were valid. Predictive equations based on multiple regression analysis for each of the five groups explained between 40 and 69% of the measured variation in each one. When used to predict measured bulk density from the European dataset, the equations explained 63% of the measured variation in mineral horizons from soil environments similar to those of the development dataset with a predictive mean percentage error of +/- 11%. The equation for organic horizons explained 29% of the measured variation in bulk density with a mean percentage error of +/- 39%. For those horizons from soil environments outside those of the development dataset, prediction of bulk density was relatively poor, even when using soil region-specific PTFs derived from its data. It was concluded that, for these soils, factors other than organic carbon, particle size, horizon depth, mechanical cultivation or parent material have a major influence on bulk density and need further investigation.