Pedotransfer functions for bias-correcting bulk density observations in the Hungarian Soil Information and Monitoring System

Bulk density (BD) is a key soil property due to its strong influence on the physical, chemical, and biological properties of soil, serving as an important indicator of soil health, compaction, and physical quality. An earlier study revealed that BD observations in the Hungarian Soil Information and Monitoring System (SIMS) might have been biased and therefore require correction. SIMS is a nationwide soil monitoring system that collects information on the temporal variability of Hungarian soils across Hungary at 1236 soil profiles. Accordingly, the objective of this research was to bias-correct BD measurements in SIMS using advanced pedotransfer functions (PTFs).

Various PTFs, including multiple linear regression, generalized additive model, cubist, random forest, and artificial neural networks, were developed based on the Hungarian Detailed Soil Hydrophysical Database and an extensive set of environmental covariates (e.g., long-term climatic data, topography and its derivatives), which serve as proxies for soil-forming factors. The developed PTFs were evaluated and compared using five times repeated 10-fold cross-validation, revealing that the random forest-based (RF) PTF outperformed other techniques, with RMSE and model efficiency coefficient values of 0.099 g cm⁻³ and 0.539, respectively. Consequently, the RF-based PTF was used to correct BD measurements in SIMS and to provide quantitative information on the uncertainty associated with the corrected BD values. The latter is essential to support end users in the proper interpretation and application of the corrected BD values. Subsequently, a dataset was compiled containing information on the SIMS profile and layer identifiers, the upper and lower depth boundaries of each soil genetic horizon, the corrected BD values, and their associated uncertainties. The dataset is publicly available on Zenodo (https://doi.org/10.5281/zenodo.16926945).

The aim of our presentation is to introduce the applied methodology, the RF-based PTF developed for bias correction of BD measurements in SIMS, and, most importantly, the resulting BD dataset compiled within the framework of this study.

Reference:

Sohrab S., Szabó B., Pásztor L., Makó A., Szatmári G., 2025: Adjusting bulk density observations in the Hungarian Soil Information and Monitoring System using pedotransfer functions. European Journal of Soil Science 76(6): e70245.