Comparative assessment of SoilGrids system with regional soil data for advancing ecosystem reporting in Bulgaria

The aim of this study is to test the suitability of the SoilGrids system for ecosystem reporting, research and monitoring. The study is conducted in the Rila Mountains in Bulgaria, an area characterised by diverse ecological factors. We propose a methodological approach to compare SoilGrids predictions with independent point observations, addressing issues of inconsistency across survey layers when combining data from different sources. The comparative analysis is discussed in respect to point data, soil type, altitude and climate. The results show that the SoilGrids represents the main soil parameters well in terms of their dynamics over the altitudinal range. There is a good agreement between the observed and predicted values for the averages of the parameters - bulk density, coarse fraction, soil organic carbon (SOC) content and SOC stock. The average measured SOC stock (0-30 cm) is 58.54 t/ha, while the average predicted SOC stock (0-30 cm) is 55.38 t/ha. However, the study also showed that the predicted values for nitrogen content are almost two times higher than the observed figures and the pH values from the SoilGrids are less acidic than those measured in the field.