Yields and Magnesium Uptake by Plants as Affected by Soil pH and Calcium Levels1

Liming of acid soils may influence Mg uptake either because of associated pH factors or because of Ca level as the result of liming. This study was conducted to determine the effect of Ca levels and soil pH on the yield and uptake of Mg by oats (Avena sativa, cultivar ‘Gary’). Treatments in one experiment included a control, 118 ppm Al as Al2(SO4)3, 506 ppm Ca as CaCO3, 506 ppm Ca as CaCO3 plus 506 ppm Ca as CaSO4, and 1,012 ppm Ca as CaCO3. In a second experiment two Mg levels (0 and 12 ppm Mg as MgSO4·7H20) were applied in combination with two Ca sources at two Ca levels (0 ppm Ca, 800 ppm Ca as CaSO4, and 800 ppm Ca as CaCO3). Uptake of Mg was not increased by the addition of CaSO4 either in combination with Al2(SO4)3 or CaCO3. Uptake of Mg was significantly greater (5% level) when 800 ppm Ca as CaCO3 was applied than when 800 ppm Ca as CaSO4 was applied. Application of Mg significantly (5% level) increased Mg uptake regardless of Ca level or source. These results suggest that soil pH level affected Mg uptake more than did Ca level.