Morphological, physical, chemical and mineralogical properties of soils from southern Corrientes province

Abstract

Modal profiles of Vertisols (Chromic Epiaquerts, El Ombú Series; Oxiaquic Hapluderts, La Esperanza Series), vertic subgroups of Mollisols (Vertic Argiudolls, Santa María Series) and Entisols (Lamellic Udipsamments, Estancia Madre Series) from Curuzú Cuatiá and Salto departments in Corrientes province were studied. The soils developed from the Solari-Serra Geral (basalts with sandstone intercalations) and Toropí-Yupoí Formations (pelitic sandstones to sandy pelites, of lacustrine origin) under a humid subtropical climate, with annual average temperatures between 19.5 and 20.5 ºC, annual average precipitation of 1491 mm (1947-2000), frequent water surpluses in autumn and sometimes in spring, seasonal water deficit of short duration, and with savannah vegetation. The objective was to relate vertic features in the profiles with the parent material and some physical and mineralogical properties. The soils display one or more of the following vertic features, to varying degrees: gilgai microrelief, diapiric-like structures (mukkara), surface cracks, slip surfaces and wedge-shaped aggregates. Argillipedoturbation was governed by the textural and mineralogical characteristics of the parent material, while the degree of expression of those features was controlled by the hydrological conditions of the soils. Soils with vertic features have between 19.9 and 46.5% total clay and more than 35% expandable minerals in the mass of the soils from the surface or 28% from the base of the A horizon. Fine silt and sometimes clay are the modal granulometric intervals. The C horizon reveals that those formations provide enough total (over 30%) and expandable clay (over 90 %) for the development of vertic features. The entisols possess high content of total clay in the buried B horizons and their clay fraction is almost totally made up of kaolinite and illite, even in the buried horizons where kaolinite increases. They have abundant content of sand in the whole profile, and the modal fraction is very fine sand, followed by fine sand, except in the buried B horizons where the modal fraction is clay. An inherited feature of the soils with vertic features from south central Corrientes province is their higher amount of expandable minerals as compared with similar soils from Entre Rios and Buenos Aires Provinces, which show a higher contribution of illite - rich loess.