The Paraná magmatic province is a Large Igneous Province (LIP) that covers approximately 1.5 x 106 km2 in South America (Rämö et al. 2016). The soils in this LIP have high agriculture potential, especially for crops and livestock, which have been leading to the intensive use of these lands. The intensive land use is performed to reach high production since new land areas acquisition is not considered due to the high monetary cost of new land areas purchase (Telles et al. 2016; Flexor and Leite 2017).
The intensive land use of these areas is performed, generally, without land use planning, disregarding soil and water conservation practices, which reduces soil quality. This land degradation leads to the incorporation of natural fragile soils, which have a low land use capacity, and a high potential for degradation, in agricultural production systems. These naturally fragile areas are composed of hill slope areas, with high erosion potential, and hydromorphic soils, influenced by shallow groundwaters, or close to rivers and water bodies used to supply anthropic and agricultural demands. Even that, agriculture has been indiscriminate performed, beyond its capacity, mainly due to the absence of prior analysis of the land use capacity based on mapping of the soil and the environmental fragility.
The soil maps available for the main part of these areas are at the reconnaissance level (1:600.000; Bhering et al. 2008). The use of these maps leads to inadequate land use and management planning at watersheds and rural properties. The absence of planning or inadequate planning has been the main reason for soil degradation. Soil maps need to be updated to obtain precise soil spatial distribution and variability of soil properties information, for proper soil management, and for conservation policies elaboration. However, traditional techniques to elaborate soil detail maps are complex and required tacit knowledge, which results in high costs and high subjectivity in the soil classes definition (Hudson 1992; Taghizadeh-Mehrjardi et al. 2015; Vasques et al. 2015).
Spatial distribution and variability of soil properties are mainly influenced by relief, on a local scale (Wolski et al. 2017). Topography acts on erosion and depositional processes, and on water content, besides defining the soil sequence in a catena (Milne 1935; McKenzie and Ryan 1999; Valtera et al. 2015; Bui et al. 2017). Topographic attributes, extracted from the Digital Elevation Models (DEM) obtained through remote sensing (Gómez-Gutiérrez et al. 2015; Massawe et al. 2018) are quantitative descriptors of relief formation. These attributes can be used to describe pedogenetic processes (Moore et al. 1993; Wilson and Gallant 2000), and allow the results extrapolation and the prediction of soil variations along the landscape (Rossiter 2018).
The high descriptive and predictive potential of topographic attributes and their close relationship with pedogenetic processes may make the combination of the topographical attributes and digital soil mapping (DSM) techniques an important tool for soil mapping. This DSM with topographic attributes combination is an alternative strategy to obtain lower subjective spatial soil data. The DSM use allows for evaluating uncertainties, refining the definition of soil classes on existing maps, and generating maps on a scale appropriate to the land use and management planning of rural properties (Minasny and McBratney 2016; Zhou et al. 2019). Furthermore, the DSM techniques can be easily replicated and used by less experienced pedologists, as they are higher objective, reaching results similar to those maps generated by experienced pedologists (Arrouays et al. 2017; Teng et al. 2018).
Topographic attributes have been used around the world in DSM to evaluate environmental impacts, erosion processes in watersheds, the materials (re)distribution on the landscape, the distribution of the soil taxonomy classes, to contribute to the Global Soil Map, to the classification of areas with potential for investment in irrigation systems for agricultural production and adequation of fragile areas. The combined analysis of different topographic attributes contributes to the comprehension of the environmental processes for influence soil formation and landscapes.
The topographic attributes as slope and curvature (Sheshukov et al. 2018), declivity, aspect, curvature plan, and curvature profile, topographic wetness index (TWI), length-slope factor (LS), and stream power index (SPI) (Osat et al. 2016), can assist in the implementation of soil conservation agricultural practices because they indicated erosive processes in the Midwest of the United States and on the distribution of the soil taxonomy classes, in the north of Iran. Elevation, slope, aspect, curvature plan and profile, multi-resolution valley bottom flatness (MrVBF), multi-resolution ridge top flatness (MrRTF), topographic position index (TPI), and TWI (Vaysse and Lagacherie 2017) were used in regression models for predicting clay content and organic carbon content in southern France and contributed with tools that may be used in the development Global Soil Map. The combiner of the topographic attributes curvature plan, slope, channel network base level (CNBL), TWI, MrVBF, and MrRTF with climatic variables (Kidd et al. 2015) possible classifier of areas with potential for investment in irrigation systems and adequation of fragile areas as in agriculture production areas in South Australia.
In Brazil, there are still few studies performed on a more detailed scale (Polidoro et al., 2016). Topographic attributes of TWI, MrVBF, and MrRTF were efficient in the prediction of soil properties in similar areas and, therefore, the generation of detailed, low-cost mapping was possible, in a watershed in southeast Brazil (Silva et al., 2015).
However, soil mapping performed with geoprocessing tools, integrated with soil legacy data is a contribution to improving the soil maps database (Giasson et al. 2015; Pelegrino et al. 2016). The topographic attributes application assists in the measurement of several soil properties and in the modeling of soil processes (Oliveira Junior et al. 2014; Wang et al. 2018; Shahbazi et al. 2019, Maganhotto et al. 2020). Therefore, geoprocessing tools to manage and integrate topographic attributes have great potential for the generation of more detailed information, with less uncertainty, lower cost, and greater speed. Information on soil types on a semi-detailed scale are necessary for adequate evaluated land use capacity and environmental fragility in watersheds (Campos et al. 2021).
We aimed to identify and select the topographic attributes that represent the variability of subtropical basalt-derived soils and that have the potential to delimit the boundaries of the different soil classes. The identified and selected topographic attributes were used to generate a semi-detailed soil map and to elaborate a land use capacity class map of the Lontra river watershed. The semi-detailed scale soil map built in n an environment of geographic information systems (GIS) and field-checked will contribute to the better identification of land use capacity classes. The use capacity map will serve as a subsidy for the evaluation of areas with inadequate use and in the planning of soil use and soil conservation in rural areas.