Chemical Composition and the Agronomical Potential of Two Types of Rock Phosphate in Sudan

ABSTRACT. This investigation was carried out to test the possibility ofusing two sources of rock phosphate from Sudan as a phosphorus fertilizer.The two types of rock phosphate examined were collectedfrom Uro and Kurun in Nuba Mountains, Western Sudan. Chemicalanalysis of rocks indicated that Uro and Kurun rock phosphates contained20.5 and 25.9% P2O5, respectively. These levels meet the universalrequirements to mark the tested rocks as good sources for plantphosphorus. Soluble phosphorus was found to be 0.001 and 0.002%P2O5 for Uro and Kurun, respectively, and the respective citratesolublephosphorus was 3.5 and 3.7% P2O5. The heavy metals contentof the rocks was also recorded.The effect of treatment, namely, fineness, temperature and calcinationon the solubility of the rock was examined for the various grainsizes tested (1.00, 0.10 and 0.01mm). The solubility was found to beinversely proportional to the grain size. Calcination was the most effectiveat temperature ranging from 700-850ºC.Based on the previous studies and confirmation measurements inthis experiment the rock samples from Uro and Kurun had a high contentof radionuclides. An experiment was, therefore, carried out to investigatethe radioactivity hazard of using these rocks in agriculture.A pot experiment, using fodder sorghum (Abu Sabeen) as a test crop,was conducted for three seasons. The phosphate rock was applied at alevel of 20 gm/4kg soil (0.5%) in the first two seasons. The resultsshowed that the radionuclide plant content in the third season waswell below the recommended level of contamination. It seems that theavailability and, hence, the absorption of radioactive heavy elementsby plants is low under the prevailing high pH of soil.