Some crop managers are concerned that repeated use of dolomite lime, which contains 10 to 15% Mg, will produce excessively high soil Mg+2 levels relative to Ca+2 and reduce cotton (Gossypium hirsutum L.) K+ uptake and yields. Two cotton field experiments were conducted on well-drained soils to determine the short- and long-term effects of lime applications containing Mg. The first test compared the short-term effects of lime with low and high Mg content on soil characteristics and cotton lint yield. This experiment was conducted at Portageville, MO, in 2000 to 2002 on a field with pH salt 4.7 to compare the effectiveness of calcite (calcium carbonate) and dolomite (calcium magnesium carbonate) lime at recommended rates for increasing cotton yields on acid soils. Averaged across 3 years, both lime sources significantly increased cotton yields by 94 to 112 kg ha-1 of lint compared with the untreated check. There were no significant differences between calcite and dolomite lime. A second experiment was conducted from 1999 to 2001 to determine whether long-term use of dolomite lime, which reduces exchangeable soil Ca:Mg ratios, would decrease plant K+ uptake and cotton yield. To produce a range of Ca:Mg ratios in a soil with near neutral pHsalt (6.2), selected rates of gypsum (CaSO4) and Epsom salt (MgSO4) were applied and incorporated in plots. Soil Ca:Mg ratios ranged from 2.5:1 to 7.6:1 (% base saturation). Whole plant tissue K, fiber quality, and lint yield were not significantly affected by exchangeable Ca:Mg ratios. This study showed that cotton farmers with well-drained Delta soils should not be concerned about potential negative effects of Mg in dolomite lime material.