Browsing by Author "Swai, Lobati Salvatory"

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    Sorption and availability of sulphur in some soils of Mbeya region
    (University of Dar es Salaam, 1980) Swai, Lobati Salvatory
    Sulphur sorption and availability were studied in ten soils from Mbeya Region. The soils contained kaolinite, hydrous iron oxides and amorphous ferrialumino silicate as the dominant clay minerals. The length of equilibration required for a near-complete equilibrium condition in the soils was investigated. A 48-hour equilibration period was found adequate and was used in the sulphate (SO4) sorption study. The soils differed widely in their SO4 sorption capacity. Soils with high SO4 sorption capacity had higher positive dpH (pH0.1nK2SO4 pH0.1N KCl) values than those with low capacity. The correlation between amount of SO4 sorbed and total Fe203, amorphous Fe203, amorphous ferrialumino silicate or organic carbon content of the soils was statistically non-significant. The SO4 sorption data for most of the soils fitted the Freundlich model. In a greenhouse pot experiment, alfalfa (Medicago sativa) was grown on eight soils at six S-fertilizer rates corresponding to six adjusted-S (equilibrium S) concentations determined from the SO4 sorption isotherm. On most of the soils, the alfalfa seedlings growing in the control pots showed S deficiency symptoms which disappeared as the plants grew older. Sulphur fertilization increased the dry matter yield of alfalfa significantly on four soils; the increase in yield on the other four soils was statistically non-significant. Sulphur fertilization also increased tissue S and S uptake by alfalfa on all the soils. The external S requirement for 95 percent of the maximum dry matter yield ranged from 0.8 to 8.2 mg S/ml, but it was less than 2.0 mg S/ml on most of the soils. The soil with lowest SO4-sorption capacity had a low (but not the lowest) external S requirement. However, there was no consistent direct or inverse relationship between SO4 sorption capacity and external S requirement. Nine indices of S availability in the soils were evaluated. The phosphate and acetate solutions extracted more SO4-S than 0.01M CaCl2 from all the soils. This indicates that a large proportion of SO4-S in the soils was in the chemi-sorbed form. The only index of S availability that was significantly correlated with the relative yield of alfalfa in the greenhouse experiment was 0.01M CaCl2 extractable S. Therefore, 0.01M CaCl2 was considered most suitable for estimation of available S in the experimental soils. *Ionic forms are used without indication of charge throughout the thesis except where charge indication is essential to the meaning.