Sistema de pastejo intensivo irrigado e atributos de um argissolo vermelho do noroeste do estado do Paraná

Abstract

Intensive Grazing System (SPI) can compromise soil attributes due to animal trampling if the entry and exit height of the forage and the water content in the soil are not controlled at the time of grazing. Soil and water are basic resources that sustain life on the planet and act as the foundations of food, fiber, and energy production systems. In this sense, the aim of this study was to evaluate soil attributes related to structure and characterize the chemical composition of soil samples collected in an area cultivated with perennial pasture irrigated by central pivot submitted to intensive grazing system. On a private farm at Amaporã County, northwest Mesoregion of the State of Paraná and in the Microregion of Paranavaí, twelve georeferenced sampling points were randomly selected in a perennial pasture irrigated by a central pivot located at the geographic coordinates (Latitude: -23.076846; Longitude: -52.747762) and altitude of 370 m above sea level for visual analysis of the soil structure through the Rapid Diagnostic of Soil Structure (DRES). In these sampling points, a total of 24 undisturbed soil samples were collected, encompassing 12 samples of the 0–10 cm layer and 12 samples of the 20–30 cm layer were collected in an area irrigated by a central pivot of private property in Amaporã County, northwest mesoregion of the state of Paraná and in the Paranavaí microregion. The soil in the study area was classified as ARGISSOLO VERMELHO Distrófico, with a sandy-loam texture, cultivated with perennial pasture irrigated by central pivot. Physical soil characterization includes particle density and particle size distribution analyzes in addition to attributes related to soil structure such as: soil bulk density, total porosity, volumetric water content and degree of compaction. The chemical composition of the soil samples was determined using a portable X-ray fluorescence spectrometer (pXRF). The magnetic susceptibility of the soil samples was determined by a magnetometer. The results of the visual assessment of the soil indicated that the structural quality index of the soil samples evaluated by means of DRES was greater than 3 at all sampling points, which indicates that no features of degradation or absence of disaggregated primary particles were observed in vertical channels of the soil layer (0–25 cm deep). Silicon (230 g kg-1), aluminum (42 g kg-1) and iron (20 g kg-1) were the most abundant chemical elements in the soil samples from both layers studied. The magnetic susceptibility per unit mass (BF) in the ovendried fine soil ranged from 3.97 to 7.89 x 10-7 m3 kg-1 with an arithmetic mean of 5.42 x 10-7 m3 kg-1 at 0–10 cm depth, being considered low probably because the soil parent material of the area is derived from the Caiuá sandstone, indicating a low presence of ferrimagnetic minerals in the different soil particle size fractions.