Weathering intensities in tropical soils evaluated by machine learning, clusterization and geophysical sensors

Abstract. Weathering is widely used for pedogenesis and soil fertility studies, once it affects several soil attributes. Understanding the intensities of weathering can provide answers for environmental issues, soil and geosciences studies. Recently, there are available geotechnologies (such as geophysics and machine learning algorithms) that can be applied in soil science to provide pedosphere information. In this research, we performed a method to evaluate weathering intensity in a heterogeneous tropical area by proximal remote sensing data acquired by geophysical and satellite images respectively. The area is located in southwest Brazil, with 184ha and we sampled 79 sites (all with soil analysis) using toposequence knowledge. Afterwards, the principal component analysis and the ideal number of clusters was determined. Then, we determine and used the ideal number of clusters, weathering index, as input data in four modelling (prediction and spatialization) algorithms to infer different weathering intensities in soils formed from the same soil parent material. The results showed that the best model performance was for the random forest reaching 3 clusters as the ideal number. The surface pixel reflectance acquired from a Synthetic Soil Image, the terrain surface convexity and digital elevation model were the covariates that most contributed to modelling processes. The model’ specificity was greater than sensitivity. The East areas over diabase such as the Nitisol presented greater weathering intensity than the Nitisol over West diabase areas. The areas over siltite/metamorphosed siltite and Lixisols presented moderate weathering rates. The relief and topographic position strongly affected the weathering, once they controlled the hydric dynamics. The geophysical variables were related to soil attributes and weathering, which contributed to modelling and clusterization processes. The different weathering rates are mainly modulated by geomorphic processes that relief, topographic position, and the associated soil types control water dynamic at the landscape and directly affect the weathering intensities.