Proper potassium (K) nutrition is critical for maximizing rice grain yields. K is very mobile within the rice plant. Older leaves are scavenged for the K needed by younger leaves. Little is know about the effect of soil-applied Magnesium (Mg) on the uptake and partitioning of K within developing rice plants. Studies in 2002 and 2003 correlated yields and tissue K levels of individual plant parts during the growing season. Better correlations were obtained later in the season, K levels decreased as the season progressed, and flag leaves were found to be a poor indication of plant K status. This study will build upon the results obtained in 2002 and 2003. It will attempt to determine the effect of soil applied Magnesium on plant uptake of K and Mg.