AbstractLaboratory experiments, using disturbed soil columns, were performed to determine solubility and downward movement of surface-applied magnesium fertilizers in three Puerto Rican Ultisols. Leaching of Mg from surface-applied granular magnesium oxide fertilizers was much slower than leaching from Epsom salts and potassium-magnesium sulfate. The inclusion of ammonium sulfate in the MgO fertilizer band resulted in solubilization of Mg from the MgO and allowed greater movement into the soil profile. When ammonium sulfate was applied with MgO, 85% of the Mg dissolved and moved deep into the profile, whereas with MgO applied alone only 15% of the Mg moved. However, in the presence of high concentrations of ammonium sulfate, the extent of Mg leaching through the soil was greater than where soluble magnesium fertilizer was applied without ammonium sulfate. Urea had a lesser solubilizing effect on MgO, and potassium chloride and triple superphosphate were ineffective.
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