Critical values of physical attributes of an Ultisol under uses in South of Brazil

Abstract

Changes in the soil structural quality have caused alterations in root growth and agricultural yield. With the purpose of finding critical values of physical parameters and alternative, viable and suitable ways of minimize the soil degradation, this study aimed at quantifying aggregate tensile strength (TS), friability (F), bull density (Bd), total porosity (Tp), macroporosity (Ma), penetration resistance (PR) and total organic carbon (TOC). Relations were established to estimate the structural quality of some parameters of an Ultisol under different uses. The study was carried out on a farm, in the rural area of RS, inserted in the Arroio Moreira waterbasin, Brazil. Disturbed and undisturbed samples were collected from the 0.00 to 0.10 m layer. Regarding TS and soil use, 900 samples were selected, totalling 2700 aggregates. Undisturbed samples (135) were collected for the evaluation of Bd, porosity and PR. The TOC was quantified using 45 aggregates through the dry combustion method. All physical parameters with exception of F are important in monitoring the structural quality.The lowest values of TS, PR and Bd were verified in the soil under fallow, and the highest ones in the soil under pasture. An inverse relation between TS and TOC and between Bd and TOC was verified. Critical values of Bd and TS to crop development might be estimated from the PR.