Assessment of Dithionite and Oxalate Extractable Iron and Aluminium Oxides on a Landscape on Basement Complex Soil in South-Western Nigeria

Abstract

The study investigats the morphological, physical and chemical characteristic of a toposequence on basement complex in Ejioku area, southwestern Nigeria on latitude 07˚28.675'N; and longitude 004˚07.219'E; 180 m above sea level at the upper slope. It terminates at the valley bottom on latitude 07˚28.756'N; and longitude 004˚07.229'E; 175 m above sea level. The topography of the site is moderately slope (not greater than 10%). The aim is to examine the two forms of sesquioxides (crystalline-dithionite extractible Fe & Al and amorphous-oxalate Fe & Al) and their distribution on the toposequence. The crystalline form of Fe oxide dominates all the positions and ranges from 7.2 g/kg at the valley bottom to 444.3 g/kg at the crest compared to the amorphous forms that range from 2.7 g/kg to 10.9 g/kg. The crystalline and amorphous aluminium oxide contents of the soils are low (2.9 g/kg-43.3 g/kg and 1.3 g/kg-8.7 g/kg respectively). There is significant negative relationship between Fed and Fe d /Fe o (r = −0.15; P < 0.01; n = 16). There is also a correlation between Fe o and Al d (r = 0.63; P < 0.01; n = 16), Fe O and Fe O /Fe d (r = 0.44; P < 0.01; n = 16), signifying a high level of weathering. The relatively high amount of Fe d virtually at all the horizons indicates that the crystalline and less active forms of the oxides exist more on the landscape and may be responsible for the non-availability of some nutrient like phosphorus that may be sorbed to their crystals lattice. All forms of Al in the soils are low especially, the oxalate extractable forms, when compare with the dithionite extractable forms. However, there is a significant correlation between Al d and Fe o /Fe d (r = 0.57; P < 0.01). As a result of high accumulation of crystalline form of Fe and Al oxide with increasing depth, most especially, at the crest/upper slope, there is greater amount of concretions, nodules and plinthites which will lead to further deterioration of the soil for agricultural purposes.

Impact of Texture on Sesquioxide Distribution in Southeastern Nigerian Soils

“…In general, bulk soil Alox was less than Ald ascribable to the neoformation process of silicate clays or the increased alteration of weathering products with time, thus serving as an index or degree of weathering (Dolui and Mustafi, 1997;Hassan et al, 2005). Equally, Alox/Ald ratio was low relative to those of other workers (Osodeke et al, 2005;Uzoho, 2014;Olatunji et al, 2015) indicating that soils were well drained and contained highly crystalline Al. Compared to Feox/Fed ratio, the Alox/Ald was higher and signifying that chemistry of the soils were dominated by aluminium.…”

“…The Ald, Alox and Alox/Ald ratio of the bulk soil ranged between 4600-6700 mg kg -1 , 750-830 mg kg -1 and 0.11-0.15 respectively (Table 3), with Ald range high relative to values reported by other workers (Hassan et al, 2005;Osayande et al, 2013;Uzoho, 2014) but low compared to ranges of other studies (Osodeke et al, 2005;Olatunji et al, 2015). Also, Alox range was high compared to others (Hassan et al, 2005;Osodeke et al, 2005;Osayande et al, 2013;Uzoho, 2014) but low relative to that of Olatunji et al (2015). In general, bulk soil Alox was less than Ald ascribable to the neoformation process of silicate clays or the increased alteration of weathering products with time, thus serving as an index or degree of weathering (Dolui and Mustafi, 1997;Hassan et al, 2005).…”

“…Dithionate and oxalate iron (Fed and Feox), aluminium (Ald and Alox), Manganese (Mnd and Mnox) and Silicon (Sid and Siox) in the bulk soil and soil particle size fractions deferred with landscape positions. Concentrations of Fed, Feox and iron activity (Feox/Fed ratio or active Fe) in the bulk soil ranged from 9300.00-11, 400.00, 390-1580 mg kg -1 and 0.04-0.17 respectively (Table 2) and low compared to ranges reported by other workers (Osodeke et al, 2005;Uzoho, 2014;Olatunji et al, 2015;Maniyunda et al, 2015). However, compared to ranges of Fed (Ojo-Atere and Ajowon, 1985;Essoka and Esu 2000) and Feox (Hassan et al, 2005) those of the soils were high.…”

“…Also, Fed and Feox correlated significantly with other sesquioxide forms besides Mnd while Feac correlated significantly (P < 0.05) with all other sesquioxide forms exception being Sid and Mnd. (Jaworska et al, 2016), Feac with Feo, Fed, and Ald and Feo with Ald (Olatunji et al, 2015). Relationship between soil properties and sesquioxide forms (Table 7) showed that sand was significantly (P < 0.05) correlated with Ald and Feox, silt with Fed, Feox, Feac, Siox and Siac, clay with Ald, Feox and Mnd while MC was with Ald, Alac, Fed, Feox, Sid and Mnd.…”

“…Distribution of sesquioxides varies with landscape positions. For instance, variation with landscape positions have been reported in soils of inland valleys (Essoka and Esu, 2000), contrasting land units (Uzoho, 2014), toposequences (Osodeke et al, 2005;Enya et al, 2011), granitic and basement complex rocks (Hassan et al, 2005;Maniyunda et al, 2015;Olatunji et al, 2015) and soil profile depths (Essoka and Esu, 2000). According to Wei et al (2010), landscape influence could be associated with the topography, drainage condition, parent materials and land use types and affects soil chemical properties and water movement conditions.…”