Drenagem interna como fator de diferenciação de Latossolos do Distrito Federal

Abstract

Resumo -O objetivo deste trabalho foi determinar a influência de características físico-hídricas dos solos em atributos diagnóstico de Latossolos. Realizou-se o levantamento de atributos morfológicos, químicos, físicos, mineralógicos e físico-hídricos de cinco perfis de Latossolos Vermelhos (LV) e cinco perfis de Latossolos Vermelho-Amarelos (LVA) petroplínticos, considerados representativos dessa classe de solos no Distrito Federal. Além da caracterização dos atributos diagnóstico, a oscilação do nível freático dos solos foi monitorada por meio de poços de observação de 2,5 m de profundidade, durante um ano. Os Latossolos estudados foram considerados semelhantes química e fisicamente. Contudo, diferiram quanto às caracterizações morfológica e mineralógica, com a presença de horizontes concrecionários e goethita nos LVA. A estabilidade da goethita nesses solos foi influenciada pela oscilação do lençol freático. Constatou-se menor condutividade hidráulica saturada e menor variação da profundidade freática nos LVA, em razão da deficiência de drenagem interna causada pela presença dos horizontes concrecionários. Os LVA apresentam, portanto, menor potencial agrícola que os LV, no Distrito Federal. As características físico-hídricas de Latossolos têm pouca influência sobre atributos diagnóstico, com exceção da mineralogia dos óxidos de ferro, que apresentam os teores de goethita aumentados em condições de baixa drenagem interna.Termos para indexação: concreções ferruginosas, condutividade hidráulica saturada, plintita, profundidade freática, regime hídrico. The internal drainage as a differentiation factor in Oxisols of Distrito Federal, BrazilAbstract -The objective of this work was to determine the influence of soil physicohydric characteristics on Oxisols diagnostic attributes. Morphological, chemical, physical, mineralogical and physicohydric attributes were surveyed in profiles of five Latossolos Vermelhos (Rhodic Haplustox, LV) and of five Latosssolos Vermelho-Amarelos (Typic Haplustox, LVA), considered representative of this kind of Oxisols in Distrito Federal, Brazil. Besides the soil diagnostic attributes characterization, the water-table oscillation was monitored using 2.5-m depth observation wells, during one year. The studied Oxisols were considered chemically and physically similar. However, they differed as to morphological and mineralogical characterization, with the presence of concretionary horizons and goethite in the LVA. Goethite stability in this soils was influenced by the water-table oscillation. The presence of concretionry horizons in LVA caused an internal drainage deficiency, which resulted in lower saturated hydraulic conductivity and lower variation of the water-table levels. Therefore, LVA soils show lower agricultural potential than LV ones, in Distrito Federal. Oxisols physicohydric characteristics have little influence on soil diagnostic attributes, except for iron oxides mineralogy, which show increased contents of goethite in low internal drainage conditions.

Surface Spectroscopy of Oxisols, Entisols and Inceptisol and Relationships with Selected Soil Properties

“…The sum of bases (S), cation exchange capacity (CEC), and base saturation (V%) were very low, featuring dystrophic soils. The contents of OM (organic matter) and OC (organic carbon) were high in most soils, as they occurred in areas of native vegetation, confirming observations of Barbosa et al (2009), Campos et al (2010, and Lacerda and Barbosa (2012).…”

“…High OM contents in surface horizons caused a reduction in RF and smoothing of the features throughout the spectral range from 350 to 2,500 nm (Dalmolin et al, 2005), as evidenced in the spectrum of the FF-III (Figure 7). The high OM content of FFc was related to higher moisture levels in the profiles, because of the impediment to free water percolation through petroplinthites and the formation of concretionary horizons in these soils, as stated by Barbosa et al (2009) andCampos et al (2010).…”

“…The soils evolved from FFc, due to differentiated conditions of erosion and pedogenesis, under the influence of the lithology of the Canastra and Bambuí Groups and local variations in relief features. Therefore, the occurrence of FFc is extremely important for the geomorphological and pedological development in the Jardim River basin, a fact given little attention in studies dealing with pedomorphogeological relations on the Central Plateau of Brazil, e.g., Motta et al (2002), Barbosa et al (2009), Campos et al (2010, and Lacerda and Barbosa (2012), among others.…”

“…Vertical water flow prevails across the toposequence, due to the high hydraulic conductivity of the granular and crumb structure of these soils under native vegetation (Campos et al, 2010). The high permeability of the Bw horizon of LV is due to structures and types of associated pores that prevent rapid water circulation (Cunha et al, 2008).…”

“…In P2 and P3 (FFc), accumulation of ferruginous concretions was observed, hampering free water infiltration into the profile, originating a wetter pedoenvironment (Motta et al, 2002). According to Barbosa et al (2009) andCampos et al (2010), the formation of a concretionary horizon in LVA of DF, as in P5, is related to its distribution and geomorphological evolution from the Chapadas Elevadas. In the subsurface, this horizon developed where the slope increases slightly, with occurrences of water table oscillations, thus resulting in the stabilization of goethite.…”