Phosphorus and Temperature Effects on Magnesium, Calcium, and Potassium in Wheat and Tall Fescue Leaves

High K fertilization often reduces leaf Mg and Ca concentration, increasing the incidence of grass tetany, while increased P treatment increases uptake and leaf concentrations of Mg and Ca in winter wheat (Triticum aestivum L.). Since P availability and uptake are often reduced at low soil temperatures, the effects of P and K nutrition on mineral element composition of wheat at two root‐zone temperatures were determined. The effects of P and NPK + Mg fertilization on leaf elemental concentrations of tall fescue (Festuca arundinacea Schreb.) grown in the field near Mt. Vernon, MO, on a Creldon silty clay loam (fine, mixed, mesic Mollic Fragiudalf) were determined. Concentration of Mg in wheat shoots was 20% higher when treated with 400 μM P than 50 μM P, and only 9% higher when root‐zone temperature was 25°C rather than 15°C. Similarly, shoot Ca concentration was 11% higher with the high P treatment. Total plant Mg uptake was 60% greater and total Ca uptake was 51% greater with high P. The higher root‐zone temperature increased total plant Mg uptake 38% and total plant Ca uptake 36%. Increasing K treatment from 400 to 800 μM decreased shoot Mg concentration 13% and shoot Ca concentration 7%. In the field, at soil temperatures <15°C, treatments of 20 or 28 kg ha−1 P increased both Mg and Ca leaf concentration of tall fescue. When leaf Mg and Ca concentrations in control plots were below 2.0 and 4.0 g mg−1 respectively, P fertilization increased Mg and Ca concentration above those thresholds considered likely to cause grass tetany. Fertilization with Mg increased leaf Mg concentration only when P fertilizer was added, but caused a decrease in leaf Ca concentration when no P fertilizer was applied. Leaf concentration and total plant uptake of Mg and Ca were more dependent on P nutrition than root temperature.