Atributos Físicos Associados à Matéria Orgânica do Solo e à Distribuição Radicular em uma transecção na Sub-Bacia Micaela, RS

Abstract

Changes in soil structure by anthropic actions have modified root growth and agricultural productivity. Understanding the variability and impacts that compromise soil quality at river basin scale is critical to proper macro scale planning. In order to understand the behavior of soil attributes, in view of the natural variability of the watersheds, samples of deformed and undisturbed soils were sampled along a transection in the Micaela sub-basin, in the municipality of Pelotas, RS. In the layers of 0.00-0.10 and 0.10-0.20 m, the following attributes were determined: bulk density (Db), total porosity (PT), macroporosity (Ma), microporosity (Mi), sand, silt, clay, penetration resistance (RP) and total organic carbon (TOC). The root system was evaluated by the profile method together with digital analysis of 2D images, and the roots were classified according to their diameter (≤ 1 and 2> 2 mm). Data were submitted to descriptive statistical analysis (position and asymmetry measurements), normality tests and data dispersion. To verify the spatial dependence, semivariograms were made and to evaluate the root system, surface maps of the analyzed variables were prepared by means of kriging or inverse square of the distance (IDW). It was found that 47.47% of the observations regarding the RP attribute are above the critical value (2 MPa) for root development. The variables Db, PT, RP, Ug, TOC, sand, clay and root mean diameter (DM) presented spatial dependence structure, being of moderate degree and semivariograms adjusted by the spherical model. The range of these attributes was higher than established in the sampling plan, making it the basis for future studies in this location. The highest root concentration predominated in the soil layer 0.00-0.10 m. The most common class was thin roots, that is, with a diameter of less than 1 mm. The thematic maps generated by kriging and IDW satisfactorily represented the spatial distribution of root attributes, supporting the qualitative analysis of interactions with physical attributes in different uses with marked contrasts between native forest and pasture.