Database extension for digital soil mapping using artificial neural networks

Abstract

Cost and time are the two most important factors conditioning soil surveys. Since these surveys provide basic information for modelling and management activities, new methods are needed to speed the soil mapping process with limited input data. In this study, the polypedon concept was used to extend the spatial representation of sampled pedons (point data) in order to train artificial neural networks (ANN) for digital soil mapping (DSM). The input database contained 97 soil profiles belonging to seven different soil series and 15 digital elevation model (DEM) attributes. Pedons were represented in raster format as 1 cell areas. The corresponding polypedons were then spatially represented by neighbouring raster cells (e.g. 2×2, ¿ up to 6×6 cells). The primary database contained 97 pedons (97 cells) that were extended up to 3492 cells (in the case of 6×6 cell regions). This approach employed test and validation areas to calculate the respective accuracies of data interpolation and extrapolation. The results showed an increase of theincreased accuracies of in training and interpolation (test area), but a poor level of accuracyaccuracy of in the extrapolation process (validation area). However, the overall precision of all predictions greatly increased considerably. Using only topographic attributes for extrapolation was not sufficient to obtain an accurate soil map. To improve prediction, other soil forming factors, such as landforms and/or geology, should also be considered as input data in the ANN. The proposed method could help to improve existing soil maps by using DSM results in areas with limited soil data, and to save time and money in soil survey work.