Effects of potassium and sodium concentrations on growth and cation accumulation in pasture species grown in sand culture

Abstract

The effects of potassium (K) and sodium (Na) on growth and cation accumulation in pasture species were examined in two sand-culture experiments. In the first experiment perennial ryegrass was subjected to a wide range of K and Na concentrations, whereas the second experiment examined the effects of potassium-sodium substitution in solution on nine pasture species. Large increases in yield were obtained by increasing K concentrations. However, near maximum yields were also observed at suboptimal K concentrations when Na was included in the nutrient solution. High yields occurred when the ryegrass tops contained at least 4.8% K (1200 m.e./kg) without Na, but only 1.4% K (360 m.e./kg) with Na. Although Na reduced K accumulation in ryegrass, the effect of K on Na accumulation was considerable. All species showed a high K selectivity against Na, with subterranean clover being the least selective. However, all species were capable of high levels of Na accumulation in the tops. It was found that Na uptake was dependent on K concentration and, to a lesser extent, on Na concentration. Calcium and magnesium uptake was reduced by K and Na, but the reduction by K was greater than that of Na at equivalent concentrations. The relevance of these findings is discussed.