Índices de agregação de solos : influência da fração areia

Abstract

Soil structuring refers to the arrangement of its mineral particles that form small structures (aggregates), generated from a complex interaction between physical, chemical and biological agents. The soil structural condition has been quantified through the size and state of the aggregates, through the aggregation indices; parameters calculated from data generated in tests that measure the aggregate ability to resist the applied rupture energy. In the calculations of these parameters, there is still no consensus on the contribution of the sand fraction to the aggregation indices, as well as whether it should be discounted in the calculations, depending on these particles’ participation in the soil aggregation process. Thus, the objective of this research was to evaluate the contribution of the coarse fraction (gravel + sand) in the soil aggregation indices. For this, an area cultivated with sugarcane was selected at the Carpina Sugarcane Experimental Station. Soil samples with preserved structure were collected for aggregate stability analysis; and part of these, converted to air-dried fine earth, were destined to the soil physical and chemical characterization. Aggregate stability analysis was carried out by the dry and wet methods, and, at the end of the process, the aggregates were dispersed to separate the sand and gravel fraction. The calculations of aggregation indices, weighted mean diameter (WMD), geometric mean diameter (GMD) and aggregate stability (AS%1 and AS%2), were performed with and without the coarse fraction mass of the aggregates to comparing each other. The evaluated soil, despite its sandy loam texture, showed good aggregation and stability, so that the removal of the sand fraction promoted small and non-significant changes in the WMD, GMD and AS%1 indices; however, in AS%2 there was significant difference. Thus, the coarse particle corrections did not promote coherent changes in the correlations between the aggregation indices and the soil characterization attributes, reinforcing that, under the conditions of this study, such corrections are not recommended.