**1. Introduction**

The chemical composition of the soil solution reflects the soil–plant-organism interplay, whereby this solution transports nutrients and other elements that supply plants and the soil biota. The effects of different soil management practices on biogeochemical flows need to be monitored and understood [1]. To understand the flow of nutrients at the soil-water interface, studies of the composition of the soil solution consider the processes of entry and exit of ions in each land-use situation [2]. The chemical elements present in the soil solution from the decomposition of leaf litter and the composition of the soil depend on various factors, namely, microbial population, plant species, temperature, groundwater flow, and soil management practices.

Various processes affect the soil solution composition, especially the mineral phase of the soil, determined by the entry and exit of minerals between the solid phase (colloidal) and a liquid fraction (solution) of the chemical elements that interact with the terrestrial and aquatic components of a watershed [3]. The investigation of the spatial–temporal variations of the chemical components susceptible to leaching to the water table or subsurface flow to land areas with lower elevation, thus reaching the watercourse beds, relies on the collection of soil solution samples [4]. The microbasins of the two streams (locally called *igarapés*) studied here, Cumaru and São João, have drainage networks predominantly regulated by the volume of groundwater stored in the soil [5]. Depending on the land use and agricultural management, in periods of high rainfall, these watersheds are subject to peak flows, with a potential to increase the loss of nutrients by leaching into deep soil layers, a process also related to the capacity of the soil to retain these nutrients [6]. In natural conditions, the soils in the basins studied are chemically poor due to the material of origin, derived from nutrient-poor sediments with low cation-exchange capacity, besides the severe action of the climate (high temperature and rainfall), causing a high weathering rate, intense leaching of nutrients and water erosion [7, 8]. These factors result in the low availability of nutrients to crops. Despite this lack of nutrients, the soils in the upland areas (*terra firme*), mainly acrisols and ferralsols, have excellent physical properties, that is, they are deep, show high infiltration rates, and are permeable, penetrable, and well-drained [7].

The objective of this study was to evaluate the composition of the soil solution in two microbasins of the Maracanã River Basin, located in the municipality of Igarapé-Açu in the eastern Amazon, subject to different land-use systems. We aim to expand knowledge about the impacts of land-use systems on water resources, improve the soil and watershed management techniques, and thus contribute to the establishment of more sustainable production systems in the region, which is mainly populated by family farmers.
