Índice relativo como avaliador da qualidade física e sua relação com atributos da fração porosa de um cambissolo.

Abstract

The Apodi Plateau has emerged as a promising pole of irrigated agriculture because of its soils agricultural potential. Considering the intensive use in these soils and assuming that the Srelative is sensitive to these changes and is related directly to the attributes of the porous fraction, this study aims to evaluate changes in physical quality of a Cambisol under pineapple crop and measure the relationship between Srelative index and porous fraction attributes. The area to be assessed at its center has the 5º 08' 05" S and 37º 54' 49" W coordinates. This is an area planted eight years ago with pineapple (Ananas comosus L. Merril) Pearl cultivar. The water supply is usually by drip irrigation and the soil is classified as Cambisol. In order to evaluate the physical quality, two soil situations were considered: under crop and native forest to a depth of 0.3 m, in the layers of 0-0.1, 0.1-0.2 and 0.2-0.3 m. In these layers disturbed and undisturbed soil samples were collected and submitted to the following physical analyses: particle size distribution, particle density, bulk density, soil air intrinsic permeability and soil water retention curve (from which S and Srelative indices were calculated). The relation of the Srelative index with the following attributes was evaluated: bulk density, porosity, macroporosity, microporosity, aeration porosity, soil air intrinsic permeability and pore continuity index. A completely randomized design was adopted with split plot scheme 2x3x5 (two soil situations: under crop and native forest; three layers: 0-0.1, 0.1-0.2 and 0.2-0.3 m; five replications). Kolmogorov-Smirnov tests were applied to verify the data normality, F for the variance analysis and Tukey for treatments means comparison, all at 5% probability. The relationship between porous fraction attributes and Srelative index was evaluated by regression analyses. It was concluded that Srelative index is sensitive to the changes imposed to the soil structure and, therefore, can be used as an indicator to quantify changes in the arrangements of its constituents; the other soil physical quality indicators agreed with Srelative showing that the area under pineapple cultivation has a better physical structure than the area under secondary forest; and Srelative index shows correlation with soil porous fraction attributes.