Propriedades físicas, mecânicas e hídricas de um argissolo submetido ao pastejo de ovinos em campo nativo

Abstract

The natural pastures characterize important food source for the creation of cattle and sheep. These often are subjected to intensive grazing schemes, which may result in physical deterioration of the soil. Sustainable strategies to the triad soil-plant-animal should be considered to enhance the restoration and maintenance of soil physical quality in fragile environments, and consequently improve the efficiency of production systems. It is hypothesized that the system of rotational native grazing pasture with the improvement of soil fertility, contributes to achieving this balance and empower soil physical recovery when it is stage of degradation. The aim of this study was to evaluate the physical, mechanical and water of an Alfisol submitted to different grazing of sheep and pasture management in an area of pasture. The specific objectives were: (i) determine the soil physical quality through evaluations of the density (Ds), macroporosity, microporosity and total porosity (Pt ) in different layers and different times, (ii) evaluate the mechanical properties by soil resistance to penetration (RP) and indicators of carrying capacity and compressibility of the soil, (iii) to assess the hydraulic properties of the soil by means of saturated hydraulic conductivity (Ksat) and soil water retention, and (iv) determine the relation between soil physical properties with the mechanical properties and water. The study was conducted on a farm in the municipality of Itaara / RS . The soil is an Alfisol, which particle size analysis indicated clay textural class to a 0,15 m depth. The studied area, in native, had been used for intensive animal beef grazing systems. The continuous and rotational grazing were conducted on native improved pasture and chemically not improved. Was carried out determinations of particle size, Ds, Pt, macro, micro, RP, pre-consolidation pressure, compression index, Ksat and water retention of soil before and after the grazing cycle (season 1 and 2 respectively). The results indicated that after the grazing cycle was obtained, especially in the treatment of improved rotational grazing field (RM), not only reduction of the values of the RP but also, besides increasing the macroporosity. The compression index showed higher values after the grazing cycle in all treatment, especially in RM, which showed increased susceptibility to suffer soil compaction independent of the different systems of grazing sheep and management of native pastures, while the soil ability support did not vary significantly. The different systems of sheep grazing did not significantly affect the hydraulic conductivity of saturated soil. The water retention of soil in the various potential tended to be smaller after the grazing cycle, which may be due to reduced microporosity.