Masters Dissertations

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Browsing Masters Dissertations by Author "Gama, Benjamin Michael"

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    Studies phosphate sorption in Tanzanian haplustox and vitrandept soils
    (University of Dar es Salaam, 1979) Gama, Benjamin Michael
    Two virgin soils, a Haplustox with appreciable amounts of kaolinite amorphous ferrialunino silicate (AFAS), and oxides and hydrous oxides of from, and a vitrandept dominant in APAS with very little crystalline minerals, were chosen for this project. Phosphate sorption in these soils were investigated with respect to length of equilibration, initial solution concentration and pH, organic matter content, and amount and nature of extractants. It was also attempted to assess the equilibrium-P required for near maximum growth of maize (Zea mays L. var. Ilonga composite) and bean (Phaseolus vulgaris L. var Canadian wonder) in the greenhouse. With respect to the length of equilibration, rapid P sorption was observed initially in both the soils but near equilibrium condition was obtained only after 24 hours. The magnitude of sorbed-P increased with increasing initial P concentration in the equilibrating solution. The initial solution pH had no effect on P sorption. Destruction of organic matter led to over three fold increase in P sorption in both the soils. The amount of desorbed-P increased with increasing volumes of water, 1M 〖KNO〗_3 or 1M 〖KSC〗_4 solution. The 〖SO〗_4^(2-) ion desorbed more P than the 〖NO〗_3^- or 〖OH〗^- ion. Studies in the greenhouse showed that dry matter yield, percent P in plant tissues and total P uptake for both the crops grown on either soil increased with increasing equilibrium-P up to certain concentration beyond which these paremeters tended to reach a plateau. On the Haplustox soil, 95 percent of the maximum maize yield was obtained at an adjusted P concentration of 9.7 pg P/ml while 2.6 pg P/ml was adequate on the Vitrandept soil. For bean, 95 percent of the maximum yield was obtained at 9.5 and 5 pg P/ml adjusted P concentration in the Vitrandept and Haplustox soils, respectively. From economic considerations, however, an adjusted P concentration lower than that required for 95 percent of the maximum yield is suggested.