Sudangrass (Sorghum sudanense, ‘Piper’ Stapf) was grown in the greenhouse in a slightly calcareous sample of Shano silt loam. The purpose of the study was to evaluate plant response to Mg and to determine any changes in Mg nutrition following individual or composite application of Mg, Ca, K and Na as nitrate compounds. The concentration of Mg in plant tissue decreased following K application and increased with each increment of Mg applied irrespective of variations in the proportions of Ca and Na included in the treatments. A base treatment including Ca, Na, and K applied with or without Mg showed a significant yield response to Mg. The Mg response was attributed to a more favorable ionic balance in the growth medium with respect to Mg because the soil was not particularly Mg deficient. Application of Mg in this case lowered the plant K concentration significantly, increased the concentration of Mg, and gave a lower K/(Ca+Mg) ratio in the foliage than was obtained without Mg. Results suggest that high levels of other nutrient cations may adversely affect the Mg nutrition of crops growing on alkaline soils not abundantly supplied with available Mg.