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
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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
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