Effects of calcium supply on uptake of calcium and selected mineral nutrients by tropical food legumes in solution culture

Abstract

Six tropical food legumes, peanut (Arachis hypogaea (L.) cv. Red Spanish), pigeonpea (Cajanus cajan (L.) Millsp. cv. Royes), guar (Cyarnopsis tetragonoloba (L.) Taub. cv. Brooks), soybean (Glycine max (L.) Merr. cv. Fitzroy), and cowpea (Vigna unguiculuta (L.) Walp. cv. Vita 4 and CPI 282 15) were grown for 20 days at six constant solution calcium concentrations (2, 12, 50, 100,500 and 2500 8M ) in flowing solution culture at pH 5.5 ¦ 0.1, with adequate inorganic nitrogen and controlled basal nutrient concentrations. Increases in solution calcium concentration from 2 to 12 8M generally increased rates of absorption of nitrogen, phosphorus, potassium, manganese and zinc, and rates of transport of magnesium and iron to plant tops. These increases in nutrient absorption and transport rates were associated with the alleviation of severe calcium deficiency. Further increases in solution calcium concentration from 12 to 2500 8M generally had no effect on potassium absorption rate, but increased absorption rates of nitrogen (by 20-130%), and phosphorus (by 90-500%), and decreased those of manganese and zinc; it also decreased rates of transport of iron and magnesium to plant tops. With guar, rates of phosphorus absorption at <2500 8M calcium were too low to maintain adequate concentrations of phosphorus in tops for maximum growth. With the remaining legumes, rates of zinc absorption at 12 8M calcium were high enough for plants to accumulate excessive concentrations of zinc (347-479 mg kg-1) in their tops. These results are discussed in relation to the adaptation of tropical food legumes to soils with low concentrations of calcium in the soil solution and the response of legumes to calcium or lime applications.