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, incre asing the incidence of grass tetany, while increased P treatment incre ases uptake and leaf concentrations of Mg and Ca in winter wheat (Trit icum aestivum L.). Since P availability and uptake are often reduced a t low soil temperatures, the effects of P and K nutrition on mineral e lement composition of wheat at two root-zone temperatures were determi ned. The effects of P and NPK+Mg fertilization on leaf elemental conce ntrations of tall fescue (Festuca arundinacea Schreb.) grown in the fi eld near Mt. Vernon, MO, on a Creldon silty clay loam (fine, mixed, me sic Mollic Fragiudalf were determined. Concentration of Mg in wheat sh oots was 20% higher when treated with 400 mu M P than 50 mu M P, and o nly 9% higher when root-zone temperature was 25 degrees C rather than 15 degrees C. Similarly, shoot Ca concentration was 11% higher with th e 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%. Inc reasing K treatment from 400 to 800 mu M decreased shoot Mg concentrat ion 13% and shoot Ca concentration 7%. In the field, at soil temperatu res <15 degrees C, treatments of 20 or 28 kg ha(-1) P increased both M g and Ca leaf concentration of tall fescue. When leaf Mg and Ca concen trations in control plots were below 2.0 and 4.0 g mg(-1) respectively , P fertilization increased Mg and Ca concentration above those thresh olds considered likely to cause grass tetany. Fertilization with Mg in creased leaf Mg concentration only when P fertilizer was added, but ca used a decrease in leaf Ca concentration when no P fertilizer was appl ied. Leaf concentration and total plant uptake of Mg and Ca were more dependent on P nutrition than root temperature.