EFFECTS OF SOIL CHEMICAL AND MINERALOGICAL COMPOSITION ON SULPHATE ADSORPTION AND DESORPTION IN TWO NIGERIAN SOILS
EFFECTS OF SOIL CHEMICAL AND MINERALOGICAL COMPOSITION ON SULPHATE ADSORPTION AND DESORPTION IN TWO NIGERIAN SOILS
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Date
1987-06
Authors
KPARMWANG, TIMMAP
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Abstract
The chemical and mineralogical composition of soils
as it affects sulphate adsorption and desorption in the
Samaru and Isoya surface and subsoils were studied.
The clay minerals important in sulphate adsorption in
the Samaru soil were kaolinite and illite; iron oxides were
haematite, ilmenite and goethite. In the Isoya soil
kaolinite was the only clay mineral, while the iron oxides
were also haematite, ilmenite and goethite.
The contents of pyrophosphate extractable iron and
aluminium '( A'l -FeP), oxalate extractable iron (FeOX) and
dithionite extractable iron and aluminium (Al-Fed), were
higher in the subsoil than in the surface horizon of the
Samaru soil. Oxalate extractable Al (Alox) was not detected
in measurable amount in this soil. In the Isoya soil, the
contents of Al-Fe , Al-Fe and Ald were higher in the surface
soil, while that of Fe, was higher in the subsoil.
In the surface soils, removal of Al-Feox and OM reduced
the soils' abilities to adsorb sulphrte, while the removal
of Al-FeQX and Al-Fep increased the soils' abilities to
adsorb sulphate. Sulphate adsorption, after the removal
of the various soil colloids, was in the order Al-Fed -
free soil<0M - free soil < untreated soil,<. Al-Fe-free soil
<Al-Feox - free soil, with mean adsorptions of 72.3,
73.7, 76.2, 77.1 and 79.7 μg S/g soil respectively. In the
(v)
subsoils, removal of each of the soil colloids reduced
the soils' abilities to adsorb sulphate. Sulphate
adsorption, after the removal of the various soil colloids
in the subsoils, was in the order Al-Fed - free soil <Al-Fe
- free soil <Al-Fep - free soil<Al-Feox - free soil<
untreated soil, with mean adsorptions of 74.7, 79.1, 80.4
and 81.3 μg S/g soil respectively. Sulphate adsorption
isotherms were found to fit the Temkin equation.
In desorption isotherms studies, the removal of
Al-Feox and Al-Fed rendered the soils sulphate free. Thus
no sulphate was released on equilibrating Al-Fe - and
Al-Fed - free soils with 0.01M CaCl2. However, sulphate
was released from all the untreated soil on equilibration,
averaging 51.8, 40.9, 14.6 and 10.2 μg SO4/g soil in the
Samaru subsoil, Samaru surface soil, Isoya surface soil
and Isoya subsoil respectively.
From the information on sulphate adsorption and
desorption studies, it is recommended that sulphur management
practice in the field should be tied up with organic matter
management, which is a retainer and also a source of plant
available sulphur. Al-Fe-oxyhydroxides, because of their
prohibitive cost of production, could be added in small
amounts as part of fillers to sulphur fertilizers to
prevent excessive loss of sulphate through leaching
Description
THESIS SUBMITTED TO THE AHMADU BELLO UNIVERSITY IN
PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
AWARD OF THE DEGREE OF MASTER OF SCIENCE
IN THE DEPARTMENT OF SOIL SCIENCE
JUNE, 1987
Keywords
SOIL CHEMICAL,, MINERALOGICAL,, COMPOSITION,, SULPHATE ADSORPTION,, DESORPTION,, TWO NIGERIAN SOILS