Abstract

ZAPPINO, Rodolfo Oscar. Hydromorphy and aquic conditions in soils of the alluvial plain of Tucumán (Argentina). Cienc. suelo [online]. 2010, vol.28, n.1, pp.79-90. ISSN 1850-2067.

The profiles of four soils with different drainage types were selected in the alluvial plain of Tucumán in order to analyze the intensity of the hydromorphy and detect which of the soils conforms to an aquic conditions. The four types were: La Aguadita (thermic Typic Udipsamment) (well-drained), La Fronterita XI (coarse loamy, illitic, thermic Typic Hapludoll) (moderately well-drained), La Fronterita X (fine loamy, illitic, thermic Aquic Argiudoll) (imperfectly drained), and Famaillá (fine, illitic, thermic Aquic Argiudoll) (imperfectly drained). The soils show endosaturation conditions for six months of the year, with an increase in water level during summer-autumn and a decrease in winter-spring. The degree of reduction was assessed in terms of the distribution of iron and manganese associated with redoximorphic features analyzed on a micromorphological scale. In the well-drained and moderately well-drained profiles, Fe_d and Mn_d show little mobility, with the respective values ranging from 0.50-0.80% and 0.03-0.06%, Mn_d / Fe_d <0.08% and underdeveloped redoximorphic features. In the profiles with imperfect drainage, the Fe_d sometimes co-migrates with and sometimes separates from clay, with the segregation of Fe_d outside the profile. Mn_d has low values (0.01-0.06%) with an increase of 0.20% in the BC of La Fronterita X, Mn/Fe_d = 0.33 and more developed redox features. The analysis suggests that the hydromorphic process increases from the moderately well-drained La Fronterita XI profile towards the imperfectly drained La Fronterita X and Famaillá profiles. The former two profiles are expressed in the Mn/Fe_d ratio and in the increasing size and abundance of redox features as observed on a micromorphological scale; and the Famaillá profile in the low mean value of Fe_d and Mn, and the presence of redoximorphic features. The Fronterita X and Famaillá profiles present the most reduced conditions among the studied soils and are assumed to conform to an aquic regime.

Keywords : Micromorpology; Redoximorfic features; Secondary Iron and Manganese.

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