ISSN 2070-7401 (Print), ISSN 2411-0280 (Online)
Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa
CURRENT PROBLEMS IN REMOTE SENSING OF THE EARTH FROM SPACE

  

Sovremennye problemy distantsionnogo zondirovaniya Zemli iz kosmosa, 2026, V. 23, No. 1, pp. 178-193

Mapping of soil acidity of Cis-Salair drained plain soils using archival data and the Random Forest algorithm

N.V. Gopp 1 
1 Institute of Soil Science and Agrochemistry SB RAS, Novosibirsk, Russia
Accepted: 20.11.2025
DOI: 10.21046/2070-7401-2026-23-1-178-193
The results of digital mapping of acidity (pH-H2O) in a 0–30 cm soil layer of the Cis-Salair drained plain (Toguchinsky District, Novosibirsk Region, Russia) are presented using archived soil data, 9 sets of predictors and the Random Forest (RF) algorithm implemented on the Google Earth Engine online platform. Archival data on soil pH for the period from 1983 to 1994 were obtained from the research materials of ZapSibNIIgiprozem (West Siberian State Scientific Research and Design and Survey Institute for Land Management). The simulation was carried out based on a different number of predictors in the set: 92 (all); 37 (relief); 26 (climate); 17 (vegetation); 10 (soil properties); 2 (spatial position); 10 (2 dominant predictors from each group of soil formation factors); 22 (5 dominant predictors from each group of soil formation factors); 42 (10 dominant predictors from each group of soil formation factors). The training dataset (TD) contained information on pH-H2O in the 0–30 cm soil layer for 612 soil profiles, and the validation dataset (VD) for 110 soil profiles. The values of the determination coefficients for models with different sets of predictors for the training sample (R2TD) were in the range of 0.70–0.86, which demonstrates high explanatory power of the models. However, the values of the determination coefficients in the validation sample (R2VD) varied in the range 0.05–0.28, which indicates a weak generalizing ability of models based on independent/new data, i.e. the model explains the variation in soil acidity slightly better than the average value. Reducing the number of predictors in the models to 42 and 22 did not lead to a significant increase in R2TD (0.85 and 0.84, respectively) and R2VD (0.25 and 0.28, respectively) compared with the model with 92 predictors (R2TD = 0.86; R2VD = 0.23). A comparison of all models showed that the model with 22 predictors has the best modeling efficiency indicators: R2TD = 0.84; R2VD = 0.28; RMSEVD = 0.44 (Root Mean Square Error); MAPEVD = 4.8 (Mean Absolute Percentage Error); MAEVD = 0.29 (Mean Absolute Error). The values of pH-H2O of soils ranged from 4.6–8.8. According to the map, the studied soils belong to groups with strongly acidic (5.0–6.0), slightly acidic (6.0–6.5), neutral (6.5–7.5) and slightly alkaline (7.5–8.5) reactions. Highly acidic and slightly acidic soils were found in the soils of the northern, western and southern parts of the Toguchinsky district, whereas the soils of the eastern and partly central parts of the region were characterized by a neutral and slightly alkaline reactions.
Keywords: predictors, SAGA GIS, FABDEM, Landsat-5 TM, SoilGrids, WorldClim, Western Siberia
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